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NORTH AMERICAN ASPEN:
ITS GROWTH AND MANAGEMENT

Thai: for the Dogma at M. S.
MORGAN S‘WJ‘E COLLEGE

Harry S. Larsen
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NORTH.AMERICAN ASPEN:

ITS GROWTH AND MANAGEMENT

By

Harry S. gfigggn

A THESIS

Submitted to the School of Graduate Studies of Michigan
State college of Agriculture and Applied Science
in partial fulfillment of the requirements

for the degree of
MASTER OF SCIENCE
Department of Forestry

1953

ACKNOWLEDGMENT

The author wiehee to express his sincere
thanks to Dr. Terrill D. Stevene without whose
uiee and patient guidance thin theeie would

never have been poeeible.

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I. ILQBiL’DUC:lfil(‘/I"IOO......OOOOOOOOOCOOOOO......OOOOOOOOO 1

II. SILVICS AND ECOLOGY OF ASPEN...0.0000000000000000. h

....

q...

The Species and Ranges of kspen.................

SiteSOOOOOOOOOOO.......OOOOOOOOOOOOOOOOO00......

O\O\

801150..........OOOOOOOOOOOO......0.00.0000...

Climate....................................... 9
Site Classificstion........................... 10
Tolerance....................................... 12
ms eneration.................................... 13
Meproduction from Seed........................ 13
Aspen's Root System........................... 18
Reproduction by Suckers..................1.... 19
Nursery and Field bractice.................... 22
Aspen and Succession............................ 25
Crifiin of Aspen Etends........................ 25
Associates.................................... 27
Succession on Aspen Iands..................... 2
Enemies of Aspen and ContrOl Leasures........... 32
Diseases...................................... 33

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Cankers....................................
Leaf Diseases...................... ..... ...
Insects......................................
Animals......................................

Fire.........OOOOOOOO......OOOOOOOOOCOOOOOOOO

Climatic factors.............................
Protective measures..........................

Growth and Yield................ .............. .

III. LASAGEngT OF ASPEN LANDS........................
Aspen Supply and Utilization..........t........
Acreages and Volumes.........................
Obstacles to Utilization.....................

Aspen Silviculture.............................
fieproduction Cuttincs........................
Intermediate Euttings........................

The Aspen Problem and Courses of Action........

IV. CONCLUSIONS......................................
V. RECOKMENDATIONS..................................

APPEFDHOO............OOOOOOOOOOOOOOOOOO0.0.0.0000...O.

BIBLIUGICXFHYOOOOO0.00.00.00.00.......OOOOOOOOOOOOOOOOO.

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IhTRODUCTION

In rebuttal to a prediction by Chief Forester F. A. Silcox
that Bend, Oregon, would be a ghost town in ten years due to
overcutting, P. Hosmer made this statement in 1939:

that we're going to do is first, start a crusade
urging the mill companies to Speed up production as
fast as they can, and cut out all the pine by l9h6.
That'll get all the ground cleared off and make it easy
to put our plan into effect; second, we're going to
take one lousy looking little shoot off a pOplar tree
and plant it right in the middle of the cut over area.
We probably won't even take the trouble to plant it —
we'll just drop it out there. It'll grow all right.

hr. hosmer's mock naivete probably has elicited a bitter
chuckle from many an eastern forester since then, as he viewed
the results of this prOposal come true in his own back yard.
Northern black cottonwood was probably the species referred to,
but the capabilities described are equally as applicable, if
not more so, to the common aspens, which have shown astonishing
aggressiveness in occupying millions of acres of forest land
logged off in the lumberman's path.

The vast areas of low-value or worthless aspen lands in
Earth America have presented a tremendous economic problem to
those peOple dependent upon them, and the question of restoring
their productivity has become ever more urgent to the Eation, as

supplies of high-qualitv timber shrink and lumber needs expand.

With the advent of uorld'fiar II interest in the availability and

supply, properties and uses, and management of aspen took a sudden
rise due to the greatly increased lumber requirements for the war
effort. Since then many new uses have been discovered for this erst-
while despised species and, faced with the realization that con- I
version would not be possible for many years to come, foresters
have been studying cultural practices for increasing the quality
and quantity of aspen yields.

Since a considerable amount of literaturehas accumulated
during-the last forty years on new widely varying aspects of
this species' growth and management it sensed that gathering all
of this material together and presenting it, in substance, in e.
single publication would be of some value to workers actively
engaged. in solving the problem of increasing the utilization of
aspen. This thesis is intended to serve- that purpose;

To the best of the author's knowledge the bibliography,
which is the basis of this wcrlc, containsvirtually all exis-
ting, published, technical literature on tho growth and man-
agement of North American aspen. In addition, a few unpublished
papers which came to the author's attention and some publica-
tions on EurOpean aspen which are prominently mentioned by
investigators here have been included. Nearly all of the pub-
lished literature'was personally reviewed by the author in
preparation for the thesis. ‘ i

No attempt has been made to present information in great

detail for obvious reasons, but a large preportion of the listed
pablicationm are.cited in the body of the text to facilitate

easy and quick reference on specific tepics. Aspen utilization
has been briefly discussed, although this is not strictly within
the confines.of the subject, because of its direct bearing on
management. On the other hand, conversion of aspen lands is not
covered , even though all references on this subject specifically
concerning aspen itself are listed, because it requires separate
treatment due to its scape and complexity.

'I‘hs...suthor, in conclusion, offers some suggestions, for
handling aspen lands to increase their contribution to the forest
scenery of the regions where they occur, but it is pointed out
that his opinions do not reflect an intimate.familiarity with the

practical aspects of the situation from first-hand observation.

~b-

SILVICS AND ECOLOGY 0F AbrnN

The Species and flanges of Aspen

North American aspen properly refers only to two species of the

genus Populus, Pepulus tremuloides Michx. and Populus grandidentata Michx.,

 

 

which are similar in their silvical characteristics, and which, where
associated, are considered one species for management purposes. Their
designated common names are quaking aSpen and bigtooth aspen respectively,
but they are also known locally by a variety of modifications of the

names aspen and poplar, such as quaking asp, American pepple, and large-

toothed peplar. The closest relative of the American aspens is European

 

aSpen, fgpulus tremula Linnaeus., a species whose growth habits closely
resemble those of our own aspens. Foresters in this country have fre-
quently drawn on the EurOpean experience with this species to supplement
data accumulated through research on North American aspen.

Quaking aspen, which has a much wider range than bigtooth aSpen,
being, in fact, the most widely distributed tree in North America, and
which makes up the bulk of the aSpen volume as well, is a somewhat variable
species. Botanically, three varieties, which are probably climatic races
(USDA, Forest Service, 19b8), are recognized (Sudworth, 1928), although

the literature generally distinguishes only a western form, ngulus tremu—

 

loides aurea Tidestrom, from the eastern form, Egpulus tremulgides Kichx.

 

 

Sudworth (193h) said that silviculturally both of these forms may be con-
sidered one species, and most dendrology books include the range of the

fermer with that of Populus tremuloides hichx., while noting that a western

 

variety exists. The evidence of the literature shows, however, that
there are some definite differences in the silvical characteristics of
the eastern and western forms which will be indicated later. Baker (1921)

separated Egpulus tremuloides aurea into two altitudinal races, but

 

these have not been officially recognized. In this thesis, "aspen"
should be understood to refer to both species and all of their varieties
or races, unless otherwise specified.

The range of quakinc aspen extends from southern Iabrador to the
southern shores of Hudson's Bay and northwesterly to the mouth of the
Lackenzie River and the valley of the Yukon River, Alaska, through the
northern states to the mountains of Pennsylvania, northwestern Missouri
and northwestern Nebraska, and through all of the mountain regions of
the west, often ascending to elevations of ten thousand feet above sea
level, to the Sierras of central California, northern Arizona, and New
hexico, the high mountain ranges of Chihuahua and to Mount San Pedro.
Martin in lower California (Sargent, 1933).

Populus grandidentata Michx. occurs from Nova Scotia through New

 

Brunswick, southern Quebec and Ontario to northern Kinnesota, southward
through the northern states to northern Delaware, southern Indiana, and
Illinois, northeastern and central Iowa, and along the Allegheny houn-
tains to North Carolina and westward to central Kentucky and Tennessee

(Sargent, 1933).

Sites

While not characteristic of the most extreme sites from the stand;
point of soil conditions or climate, aspen apparently occurs on a wider
variety of sites than any other North American tree. In contrast, however,
it is very sensitive to site quality; its growth, form, vigor, and
maturity are largely governed by the site on which it occurs.

§gil§3 Baker (1925) stated that aspen grows in practically every
variety of soil in the climatic belt to which it is suited from loamy
sands in parts of the western yellow-pine type to heavy clays charac-
teristic of parts of central Utah, although stand develOpment varies
considerably with soil differences. Kittredge (1938) reported that sampling
of aspen communities in northern hinnesota and disconsin found it occurring
on fifty—four different soil types, and expressed the Opinion that it
probably occurs on as many more types which did not happen to be represen-
ted by any of the plots. Roe (1935) claimed that aspen occurs on all
soil types, in the Lake States, although Kittredge (1938) said it is
rarely found, if at all, on dry sandy outwash formations, and less favor-
able peat deposits. Alberta aspen occurs over a wide range of edaphic
conditions, including dry knolls, moist river flats, and such soils as
loam, clay and sandy (Loss, 1932). During investigations in the lake
States, with a grouping of soils accordin” to surface geological forma-
tion, aspen was found on all except the coarser sands of glacial outwash
and the shallowest soils of the rock outcrops (Kittredge and Gevorkiantz,
1929). The only soil limitation discovered was in the deep, medium or

coarse sandy soils, which are least retentive of moisture and low in their

content of nitrogen, lime, and other nutrients. These sandy soils are
characterized by less than ten per cent of silt and clay, less than 0.03
per cent of nitrogen, less than 0.2 per cent of lime and a hygroscopic
coefficient of about two per cent or less. Organic matter was as low as
one per cent, and acidity varied from extremely acid with a pH as low

as h.3, to slightly acid or neutral.

DeSpite aspens adaptability to a wide range of soil conditions, its
growth and deveIOpment are very sensitive to soil quality. On good soils,
except near the limits of its range, aspen is a relatively tall, well-
formed, and thrifty tree, while poor soils cause it to be short, of
scrubby form, and to decay at an early age.

For its best growth, quaking aspen reouires a deep, fertile, moist
but well-drained, loam soil. Particularly, it prefers moist situations
with adequate drainage. In Utah, however, aspen will grow on average
sites where there are no water supplies except from rainfall and where
the annual precipitation is as low as 17 inches, of which only a little
more than five inches falls in the growing season (Baker, 1925). This may
indicate that the western variety is somewhat more drought resistant.
Stoeckeler (l9h8) found that texture, which affects the aeration and mois-
ture relations of the surface soil, showed a good relation to site class
and growth rate Optimum for quaking aspen being about 50 per cent of
silteplus-clay. Permanent water tables at three to seven feet below the
surface of light sandy soils added about 15 feet to the site-index.
Studies in Connecticut (Lunt and Baltz, l9hb) showed that aspen excelled

in basal area on moister sites. 0n relatively sterile sandy soils in

'Wisconsin, height growth of quaking aspen was significantly greater on
sites having a higher water table and content of organic matter (Wilde
and Pronin, 1950).

Bigtooth aspen seems to be less exacting, at least in respect to
moisture requirements. Robinove and Horton (1929) observed that in the

region about Douglas Lake, Michigan, Populus tremuloides was the domi-

 

nant tree in the lowlands containing a lot of organic matter, with very

few Populus grandidentata. The reverse was true on the sandy uplands.

 

Gates (1930) reported this same situation from ecological studies of the
aspen association in Michigan. Stoeckeler (19h8) found bigtooth aspen
on plots ranging from 6 to h2 per cent of silt-plus-clay, but not on
heavier soils. Quaking aspen, however, was found on soils ranging from
12 to 81 per cent of silt-plus-clay. These facts, and its occurrence

on the knolls and drier sites, led Stoeckeler to believe that bigtooth
aspen requires the better-drained, better-aerated soils.

That fertility, as well as suitable moisture relations, is necessary
for good growth was shown by Wilde and Paul (l9h8), who found that in
Spite of an accessible ground water table, growth, specific gravity, and
alpha cellulose content all were lower on impoverished soils in Wisconsin,
than on soils of reasonably high fertility. A high site index soil in
Wisconsin (site index 82) had abundant lime, phosphorous, potash, and
magnesium in the 82 horizon and in the true parent material (horizon 02)
(Stoeckeler, l9h8). The average annual growth on this site was 55 cubic
feet per acre, contrasted with 11 cubic feet on the poorest site examined.
Abundant lime was characteristic of excellent aspen soils and evidently

contributes to greater longevity and soundness.

Conversely, wilde, Buran, and Galloway (1937) found that the fer-
tilizing value of Aspen-Birch duff developed on heavy, morainic or outwash
soils had a decidedly lower fertilizing value than the litter of hardwood-
hemlock types developed on better soils.

Stoeckeler (l9h8) considered fertility less important for bigtooth
aspen. In hisconsin, bigtooth aspen, on similar sites, had a lower site
index than quaking aspen, which Wilde and Paul (l9h8) interpreted to mean
that the former is thus more exacting. However, bigtooth aSpen is normally
a somewhat smaller, shorter-lived tree.

It should be pointed out that information about the effect of soils,
or single soil factors on the growth of aspen, is still very limited.
hereover, Specific studies of this phase of the aspen problem have been
undertaken only in the Lake States where aspen grows largely on podzolic

soils of glacial origin, developed under relatively uniform climate.

Clinete. In spite of the great extent of aSpen's range, in latitude
as well as longitude, the sites on which it is capable of forming con-
tinuous stands, are characterized by a cool, fairly moist climate, with
long winters and short growing seasons.

The upper and northern limits of elevation and latitude, respectively,
of aSpens occurrence are probably controlled y insufficient length of
growing season, low growing season temperatures, or both. The northern
limit approximates the July isotherm of 13 degrees Centigrade (Halliday,
l9h3), while in the American rookies the upper limit has an average annual
temperature of less than two degrees Centigrade (Baker, 1925). In Alaska

it grows up to elevations in protected gulches of from 2,000 to 3,500

-10...

feet. At these limits aspen is low, shrubby, and exists mostly in
protected situations and sites with a southern aSpect.

The lower and southern limits of aSpens range indicate that they
are determined by insufficient water supply during the growing season.
Over most of its northern territory aspen receives 30 to DO inches of
rainfall annually, and thus even along its southern limit in the Lake
States and the northeastern part of the United States, it comes down
to, or close to, sea level. In the drier, western part of the United
States, however, the aspen zone is elevated as the range extends south-
ward. Where rainfall is low aspen forms stands only on sites which have
exceptional soil moisture, and here they are poorly develOped and become
decadent at an early age (Baker, 1925). fispen does extend out into the
plains regions, but only along water courses where the water table is

always accessible to part of its root system.

Site classification. Aspen quality, yields, and rotations are so de-

 

pendent upon site quality that site classification is absolutely necessary
for intelligent management. The most accurate evaluation of site is,

of course, provided by the growth of aspen itself. Site index, the height
of the dominant stand at an arbitrarily chosen age, is the usual criterion
accepted. Evidence that this is a better criterion of habitat produc-
tivity than is volume growth has been presented by Kittredge (1938).

Baker (1925) reCOgnized five site oualities in the Central Rocky Lountain
region and described them as to soil, topography, and elevation. his

site indices are about twenty feet lower for each class at a given age

than are indices of corresponding classes prepared for the Lake States

-11-

(Kittredge and Gevorkiantz, 1929). weigle and Frothingham (1911)
decided on a division into three site quality classes but did not
describe the sites for future reference.

Stands under about twenty years of age are too young for site
index to be accurately determined by direct measurement, however,
(Stoeckeler, l9h3) and thus the method has only limited utility. In
order to establish some other basis for predicting the site index of
young aspen stands, which make up a large percentage of the aspen type
in the accessible regions, a number of investigators have attempted to
discover correlations between various site characteristics and site
quality. Uround vegetation Species, or plant indicators, have been
classified by some as a scale of site duality because of their general
confinement to a particular site or sites (Kittredge, 1938; Sisam,_
1935; Lake States Forest Experiment Station, 1935; and Stoeckeler, l9h8).
A table of plant indicators has been compiled for the Lake States
according to climax associations, telling with which of these associa-
tions each is found, and rating it according to its constancy (Rudolf,
1950). This will be of great assistance in planning conversion of aSpen
lands to other species. Original cover types, revealed from records or
evidence on the land itself, such as relicts or adjacent types are
another guide (Kittredge and Gevorkiantz, 1929; Gates, 1930; lake btates
Forest Experiment Station, 1935; and Stoeckeler, l9h8).

Soil quality is the most logical indirect measure of site quality
since it comprises a large prOportion of the complex of factors contri-
buting to "site", but forest soils are still an embryonic science, and

information on aspen soils in particular is very fragmentary. However,

-12-

two valuable studies have been made by Kittredge (1938) and Stoeckeler
(19w). Kittredge made habitat classifications according to soil tex-
ture, surface geological formation, a combination of texture and surface
fermation, and soil type and profile groups. Ihis is a series which
comprises successively larger preportions of the total number of edaphic
factors which influence the floristic composition and growth of plant
communities. Correlations between mean site index of sepen and the

soil classifications become successively closer as larger proportions

of the growth factors were represented. Soil profile groups had a corree
lstion coefficient of 0.778. Stoeckeler concluded from his study that
soil class, as Judged by texture of the A and B horizons and pH of the
subsoil, and severity of fires (which markedly reduce soil productivity)
are the best bases for judgment. lb set up five soil classes which
cover in e general way the range of site index classes fer aspen as de-

fined by Kittredge and Gevorkiants (1929).
Tolerance

Asped; extreme intolerance is wellrknown. There is no disagreement
that aspen is practically, if not the most, intolerant tree in North
America (weigle and Frothingham, 1911; Baker, 1925; Cheyney, 19h23 and
Toumey and Kerstian, 19h7). taker reserved judgment in the case of lum-
‘ber pine, figgg,flexiles James, but regardless, aspen is less tolerant
‘than its associates everywhere. It cannot reproduce itself under its
iown shade, for this intolerance is true from the seedling or sucker stage

to old age. In a series of diameter limit cuttings in a h3 year old

stand of aspen, the height growth of the resulting suckers was found

to bear a direct relation to the degree of cutting (Zehngraff, 19h7).
Weigle and Frothingham (1911) believed that root sprouts or suckers are
more intolerant than seedlings, although there is still no conclusive
proof of this.

Fortunately, aspen stands quickly differentiate into crown classes,
dominance being expressed by the more vigorous individuals, and stagna-
tion rarely occurs. Young aSpen stands are usually very dense, but
competition on the average site reduces the number of trees from 2,300
at twenty years to 295 at seventy years (Kittredge and Gevorkiantz, 1929).
On the other hand, the degree of dominance expressed in aSpen stands seems
to vary with site quality, for yield tables show a considerably larger
number of trees per acre, at equal stand heights, on poorer sites.

Aspens intolerance means that it can be maintained as a pure type
for more than one or two rotations only by protecting it against compe—
tition. This fact, together with its singular reproductive features,
almost entirely determine the silvicultural methods used in aSpen manage-

ment.
Regeneration

Reproduction from seed. Aspens begin to bear seed when comparatively

 

young. Thrifty trees may begin to bear when only twenty years old, (neigle
and Frothingham, 1911) and aspen continues to bear seed throughout its
lifetime, with good crops coming every four to five years and light crops

during most of the intervening years (U.S.D.A., Forest Service, 19h8).

-m-

Optimum years for seed production are between the ages of SO and 70.
Aspen is dioecious, as are all other willows and poplars. The flowers
are borne about ten days before leafing in April and May, the exact time
depending upon region, site, and the beginning of the growing season,
and they mature from May through June. It was found that there is prac-
tically no difference in the characteristics of the seeds of Populus

tremuloides and POpulus grandidentata (Faust, 1936).

 

 

In the north and east sections of its range, aspen produces its
almost minute, tufted seed in great abundance. At the height of diSpersal,
masses of the white "cotton" may accumulate to depths of several inches
in depressions. Seed is distributed in effective quantities for long
distances (Kittredge and Gevorkiantz, 1929) by air and water, and germi-
nation takes place within a day or two if suitable seedbeds are present.
Viability of fertile seed is high, averaging 99 per cent for POpulus

grandidentata (U.S.D.A., Forest Service, 19h8). Estimates of the length

 

of time over which seeds remain viable under natural conditions generally
agree on about two weeks to a month varying with local environmental
conditions (Jeigle and Frothingham, 1911; Kittredge and Gevorkiantz, 1929;
Moss, 1938; Johnson, 19b6; and U.S.D.A. Forest Service, 19h8). From
observations and repeated tests, it is evident that seeds of both species
of aSpen will germinate under a varied range of environmental conditions
as long as sufficient moisture is provided. Germination will even con-
tinue unhampered when the seeds are totally submerged in water and can
occur after several weeks of freezing (Faust, 1936). Faust said that

when there is sufficient rainfall, there are usually thousands of

-15-

seedlings germinating on the old leaves or moist soil under or near the
mature trees.

1% All of this would seem to indicate prolific reproduction of aspen
from seed while in actuality reproduction from seed plays a very minor
role in the establishment and maintenance of aSpen stands. Seedlings
are usually only of importance in filling in occasional Openings in
other forest types, although large areas, particularly fresh burns or
recently lOgged areas where the mineral soil is extensively eXposed, are
sometimes invaded primarily by seedling reproduction. Trees of seedling
origin are quite rare in the Rocky Mountains of the United States, where h

the western variety of aspen, Populus tremuloides aurea, grows. Baker

 

(1925) made a search for seedlings in this region during the years 1913
through 1916, but could find none.’ Only two instances of the occurrence
of seedlings of western aSpen have been reported since that time (bllison,
l9h3; Larson, 19hh). Baker advanced two reasons for the rarity of seed-
lings: (1) Poor seed crOps. The number of trees producing pistillate
flowers is small, and these bear only occasionally. Only about five per
cent at most of these succeed in producing and dispersing normal seed.
Staminate trees are more numerous than the pistillate trees, but even
these fail to cover any considerable percentage of the total aspen covered
area, and are usually a great distance from the flowering pistillate
trees. In addition many of the staminate catkins drop off before reaching
maturity, and a large portion of the remaining pollen crop is abortive.
(2) At the time of seed diSpersal in the west, the surface soil is dry

and showers are infrequent, so that germination except in local wet places

is extremely unlikely in the short period of viability the seeds are
known to have.

Weigle and Frothingham (1911) estimated that not more than half
of the trees, referring to the eastern variety of aSpen, are seed pro-
ducers and contended that a large proportion of the seed are abortive.
Nevertheless, the production of viable seed appears to be adequate when
conditions are propitious for seedling growth. Therefore, the scarcity
of seedling reproduction of eastern aspen is probably mainly due to in-
frequent occurrence of favorable germinating conditions and high mor-
tality after germination. Bare soil is the first requisite for seedling
establishment. ‘Weigle and Frothingham (1911) stated that unless the
seeds fall on mineral soil - on recently burned over or cleared land‘
or on other aspen spots not covered with vegetation or undecomposed leaf
litter - their chances for growth are very small. In a cut-over hard-
wood area in northern Michigan which was reclothed by aSpen, the young
trees were confined mostly to areas where the mineral soil was exposed
by acts of logging, such as skid rows, yarding sites, etc. (Buttrick,
1921).

A moist seedbed is a second requirement, if the seedlings are to
have any chance of survival. Kittredge and Gevorkiantz (1929) observed
that seedlings start abundantly only in the occasional year in which good
rains occur and the ground is thoroughly moist during the brief period
while the seeds are falling and retain their vitality. Moss (1933) found
evidence that establishment of aspen seedlings under natural conditions
occurs only when the surface layer of soil is continuously moist during

at least the first week of their growth.

Even when these conditions are met, seedlings may be killed by fungi
or later by heat or drought (U.S.D.A., Forest Service, l9h8). If the
seedlings do become established, there is a strong possibility of later
overtOpping by brush or weeds (Zehngraff, 19h9), since seedlings do
not have as rapid growth as suckers.

As a result of exposure to all these hazards, only a very small
percentage of aspen seedlings ever gets beyond a few inches in height.

Although seedling reproduction of aspen is of little consequence
to the forest manager at present, there are some indications that it may
have some significance in the future. As noted above, Weigle and
Frothingham (1911) believed that seedlings are less intolerant than
sprouts. They also stated that, "trees which sprout repeatedly, . . .
tend to 'run out' after a few generations, and it becomes necessary to
infuse 'new blood' by introducing seedlings". There has been conjecture
about both the European and American aspens as to whether trees of sprout
origin are less vigorous, shorter—lived, and susceptible to infection
through the parent root system. This will be discussed later. Barth
(19b2) contended that seedling European aspen have better form, thinner
branches, and better height growth, and are less susceptible to rot than
trees of sucker origin. On the other hand, Shirley (l9hl) asserted that
there is no evidence to indicate that stands of sprout origin are any
less vigorous than those of seedling origin, and indeed it is true that
no concrete proof of seedling superiority in any respect has ever been

presented.

Aspen's root system. The root system of aspen is of particular

 

importance because of its dependence upon root suckers for reproduction.

A distinguishing feature of the aspen root system is the fact that the

many root suckers make it very difficult to distinguish individual root
systems except in the case of small seedlings (Day, l9bh). Original parent
trees usually must be traced by age and size relations of the roots.

Day (19hh) and Baker (1925) both described aspens root system as
shallow and widespread with few or no taproots. Day found that sinkers
or vertical roots may descend to considerable depth under some conditions,
one having reached a depth of seven and one—half feet. These sinkers
generally descend in old root channels and their course and depth seem
to depend largely upon the location of the former roots.

Baker discovered the ultimate feeding roots in all levels down to
two or three feet, though most frequently from six inches to two feet;
while Day observed practically the entire lateral root system to be con-
fined to the top foot of soil. In many cases nearly all of the lateral
roots were found in the t0p six inches of soil. Baker observed that Sprouts
appear where the roots rise close to the surface (four inches or less,
according to Day), especially where two very shallow roots cross and
the upper is brought very near the top of the soil. He believed that
certain small roots are devoted primarily to reproduction, since they
run for long distances in the shallower soil layers without much change
or furcation and with practically no feeding rootlets. Suckers arise
from the root collar of the parent trees and on the stumps, as well as

from the roots, but these comprise less than ten per cent of the total

-19-

(Baker, 1925). Both investigators found a thickening of the root at

its junction with the sucker. This was confined to or most pronounced
on the side away from the parent tree, which Day interpreted as an indi—
cation of translocation of food material produced in the leaves toward

the growing tip of the root rather than toward the parent tree.

figproduction by suckers. The importance of sucker reproduction

 

cannot be stressed too much for it is their extremely prolific and

rapid production which accounts for the tremendous acreage and economic
significance of the aspen type in North America today. Aspens suckering
ability begins at a very early age. 5eedlings only two years old may
produce suckers, at which time the lateral roots are four to six feet
long (Day, 19hh). This sprouting ability remains sufficiently unimpaired
at the maximum ages reached by aspen to insure well-stocked stands.

Proof of this is supplied by an experiment conducted in Utah, in which
acre plots of 70, 90, and 110 year-old aSpen stands were clear cut
(Saker, 1925). The 100 year-old plot, which had borne about one thousand
trees, produced more than 50,000 suckers under somewhat less favorable
conditions than the other two plots, which both yielded over 100,000
trees from about the same original stocking. Kittredge and devorkiantz
(1929) confirmed this ability, citing the case of a 95 year-old uncut
stand in the Lake States (this is comparable to a much older stand on

the Rocky Mountains), which had 2,300 suckers of recent origin to the
acre. Both authorities found the age of maximum production to be 70

years. Since rotations of aspen under management should never exceed

70, or at the maximum 80 years, age should have no significance under
normal conditions in obtaining adequate reproduction. Neither, apparently,
is the health of the parent tree involved, for Heigle and Frothingham
(1911) said that badly decayed aspens are also capable of producing sprouts
profusely. According to Reim (1935), occurrence of sprouts of EurOpean
aSpen is little affected by site differences.

A number of other factors can materially affect the production of
root sUckers, however, most important of which are degree of cutting,
season of cutting, fire, and artificial stimulation by disking. Sprouting
occurs continually in aspen stands, but owing to intolerance, the sprouts
rarely live longer than a few years. In young stands sprouts are rare,
but as the stand breaks up with over maturity, they become numerous,
forming an understory, if light is sufficient (Baker, 1925). Kittredge
(1929) said that the relation of the number of suckers to the density of
the parent stand is less well-marked (meaning less consistent) than the
relation to age, but that the number of suckers decreases and rarely
exceeds 600 to the acre in stands that have more than 250 to the acre.
Actually, the production of suckers in natural stands is usually suffi-
cient to maintain adequate stocking, but the forest manager requires
fully stocked even-aged stands. A study in the Lake States, on the
possibility of converting aspen lands to conifers, revealed that clear-
cutting produced only a few more than an uncut plot. Zehngraff (19b?
and 19h9) reported that reproduction is not always adequate if cull trees
are left. In addition, the defective and undersized trees, which are

often left in cutting, and brush which thrives better in partial shade

than aspen, will suppress the young aspen growth and produce low yield,
poor quality stands.

If logging or fire occurs during the growing season, particularly
the latter part, suckering is much less prolific than during the dormant
season (weigle and Frothingham, 1911; Baker, 1925; Zehngraff, 19h6;'
Stoeckeler, 19h7; Zehngraff, 19b9). According to baker Sprouting was
merely delayed for one or two years and ultimate stocking was equal to
areas cut during the dormant season. Season of cutting did not appear to
affect height growth, after the third year following cutting. In con—
trast, Stoeckeler obtained directly opposite results. Zehngraff (19h6)
found that on areas logged during the spring, suckers are not produced
until midsummer, and that some of them are winter killed as a consequence
of not being thoroughly hardened-off by fall. Summer logged areas may
not produce suckers until mid-summer of the following year, by which
time brush provides severe competition.

Fire has long been recognized as the biggest single factor in the
tremendous spread of the aspen type. Shirley (1921) expressed the opinion
that stimulation of the growth of aspen suckers produced by light burning
is due to increased heat absorption of the blackened soil surface. The
soil, as a result, warms up earlier and remains warmer during the early
part of the growing season, and he speculated that the increased soil
temperature would stimulate chemical activity in old roots, thus making
stored food more rapidly available for suckers. The advantage in numbers
and growth of the suckers disappeared after the first year when the sur_
face was covered with leaves of first year suckers. Of course, fire first

makes this possible by thinning or removing the overhead stand on forested

land, and Weigle and Frothingham (1911) said that fires severe enough
to kill full-grown trees may not destroy the sprout-producing capacity
of the roots.

Recently, disking has been shown to be a cheap and effective treat-
ment for increasing stocking of poorly stocked aspen lands (Zillgitt,
1951). Increased stocking in one instance was due largely to natural
seeding, when the disking coincided with a bumper seed crop and abundant
rainfall in the first-year growing season.

Weigle and Frothingham (1911) said that experiments with European
aspen, which they felt were applicable to the American species, showed
that suckers are not produced from roots covered with more than six inches
of clay and sod, although they will develop abundantly if the soil above
the roots is loose and only two inches thick. This illustrates the

necessity of good soil aeration.

Nursery and field practice. Zasada reported in 1950 that regenera-

 

tion by planting and seeding was still untried in this country, and,

insofar as the author knows, it has not been experimented with for other
than shade and ornamental plantings. If it should be found feasible to
utilize artificial methods of regeneration in the future, early attempts
will have to be based largely on practices used with the related American
poplars, a summary of which is available in the Forest Service's recently
published "woody Plant Seed Manual" (U.S.U.A., Forest Service, l9h8), and

on the very excellent work done with curopean aspen. Some of the references
on the latter are Yanchevsky (190b), Anonymous (1923), Reim (1935), Earth

(19u2), and Gray (l9h9).

Certain basic requirements for successful cultivation of all species
of p0p1ar seedlings are evident. Seed should be of local origin, and
preferably collected from healthy well-formed trees producing a high
percentage of large well-filled seed. Collection should be made as soon
as the pappus is visible and the seed immediately dried by spreading out
in a thin layer, if possible in a cool, dry room to avoid exposure to
strong wind and sunlight. (Prompt sowing after drying is necessary for
high germination, and cleaned seed or ripe catkins (inserted in the seed
bed) afford greater success than seed containing down.

Seed beds must have light, fresh, fertile soil, and the surface layer,
particularly, should be fine-textured. Strip sowing facilitates weeding
and reduces competition. EJeei may be firmed into the soil, but covering
is to be avoided. Seed beds must be kept constantly moist, but not
saturated, for about two weeks after germination. 'Watering should be
frequent and light, using a fine spray to prevent disturbance of the seed
bed. Protection from sun, rain and wind with some covering is necessary
at least until the first leaves appear, after which it should be gradually
reduced. Covering must be in such a manner as to insure adequate ventila-
tion, however. Immediate steps Should be taken to protect the seedlings
from disease or insects at the first sign of their appearance. Planting
stock should be at least two years old, advisedly transplants, for forest
plantations.

P few basic studies have been carried out on the problem of optimum
storage and germinating conditions for seed of American aspen. Faust

obtained greatest longevity of stored seed when they were dried for three

to eight days, immediately upon collection, in a room at about 2h to 25
degrees Centigrade, and stored at a constant low temperature of about

5 degrees Centigrade. She observed that seeds germinate whenever there is
sufficient moisture (even when submerged) between 0 and 35 degrees Cen-
tigrade; sturdiest seedlings germinated at S to 29 degrees Centigrade.
Ross (1938) and Johnson (19h6) both found the relative humidity at which
seed is stored to be of paramount importance in longevity. Moss recom-
mended 10, and Johnson 20, per cent. moss, in addition, experimented
with various storage temperatures and concluded that —5 degrees Centigrade
was Optimum; seeds stored at this temperature showed "remarkable prolon-
gation of life." Johnson did not specify any storage temperature, but

seeds of POpulus tremuloides and Populus grandidentata retained viability

 

 

for LSS and 555 days, respectively, at the recommended relative humidity
of 20 per cent.

Attempts at prepagation of aspen by cuttings have generally achieved
such a low degree of success that its feasibility on a commercial scale
has never been credited. Snow (1938), however, succeeded in obtaining
rootings of dormant cuttings to an extent of sixty-five per cent when
they were taken at the preper time, and given optimum chemical treatment.
Cuttings taken in January and early February were almost all negative,
while best results were obtained on those taken in the latter part of
March just as the leaf buds were beginning to swell. Chemical treatment
was with indoleébutyric acid; the most effective range of treatment was

within S to 20 grams of acid for a period of 22 to 51 hours.

Aspen and Succession

Origin of aspen stands. Originally, aspen was a relatively unim-

 

portant, secondary species, throughout almost its entire range. The only
region in which the aSpen type (defined by the Forest Service in 1913

as: "A stand containing 60 per cent or more of aspen, often nearly pure,
but also with various conifers in mixture.") formed extensive stands

was at the transition to grassland in the Middle West, a band of Pepulus

tremuloides some fifty miles wide (toss, 1932). In the forest formations

 

through which it grows, the boreal forest of Canada, Alaska, and the nor-
thern parts of the Lake States and New mngland; the Rocky Kountain forest
complex; and the northern section of the deciduous forest formation in

the southern parts of New England and the Lake States, aspen occurred as
scattered trees throughout the old-growth forest, with the exception of
small patches where lightning or Indians had started fires. The creation
of the enormous acreages of aspen which now exist in much of these regions
paralled the develOpment of the logging industry and the following land
settlement.

These were only indirect, or secondary, factors, however. Fire has
been called "the great introducing agent of aSpens" (Heigle and Frothingé
ham, 1911), and correctly so. Logging, and abandoned farm land certainly
offered opportunity for aSpen to take over a great deal of land, but they
did not have the sweeping and lasting effects which the fires that inevi-

tably followed did.

A very clear and concise account of the story was given by Kittredge
and Gevorkiantz (1929) for the Lake States, where the largest acreages
of aspen exist. Cutting in the Lake States was at first only in the
valuable white pine type. As white pine became more scarce and other
species later became more valuable, the poorer stands of white pine,
mixtures of white and Norway pine, and of white pine and hardwood-hemlock
were successively cut over, many of them several times in repeated cullings.

In the process, most of the aSpen stems were broken off, and suckers
sprang up. The hazardous conditions of the slash—covered lands and the
lack of public regard for fire protection resulted in frequent widespread
fires, with aspen the beneficiary. hhch of the cut-over land burned
several times in the ten or twenty years following cutting. Each fire
cleared the ground of shade-giving vegetation, exposed the mineral soil,
and facilitated sprouting by killing the tree trunks without killing the
roots, except in the case of severe ground fires. And so, with each fire
aspen Sprouts became more abundant, and the aspen type more extensive.

In the old-growth stands, white pine, spruce, or balsam fir seedlings
were usually on the ground as advance growth. Occasional areas and
patches of land escaped the fires and this advance growth became an under-
story in the sucker stands of aspen which ouickly overtOpped it, by virtue
of their rapid growth. Some small, or defective trees of the original
type were left in the early logging, providing a seed source, but most
of these trees were later destroyed by wind storms and fires. On the
whole, therefore, mixed stands of aspen and conifers are not common or

extensive.

-27-

Baker (1925) described a process similar to this in the Rocky
Mountain region, with the exception that he believes progressive drying
of the climate has hindered the reproduction of the conifers and made
them grow in open stands, thus helping to prevent the exclusion of aspen
by suppression, which at the same time is not subjected to the critical

period of germination and the seedling stage of life.

Associates. As is true with most pioneer species, the factors which

 

establish the aspen type tend to exclude most other species of trees,

since they are characteristic of associations nearer the climax unless

they are themselves pioneer Species. Thus there are few Species of trees
which are typical associates of the aspen type, which technically should
probably be termed a consociation. Paper birch is the most common of

the few typical associates (Kittredge and Gevorkiantz, 1929). In the

East, gray birch may occur in place of paper birch (Cheyney, l9h2).

Weigle and Frothingham (1911) said that the most common companions of aspen
in restocking burned over lands in the Northeast are paper birch and pin
or "fire cherry."

The trees which actually are associated with aspen on a particular
site will depend upon a variety of factors, operating singly or in com-
bination, among which are the quality of the Site, former cover, degree
of logging, number of fires, length of time ensuing major disturbances,
seeding habits of the various species, and proximity of other types.
According to Kittredge and Gevorkiantz (1929) the other species associated
with aspen in the Lake States in order of their abundance are balsam fir,

white pine, white Spruce, black Spruce, sugar maple, red maple, Norway

..2 a.

pine, jack pine, elm, red oak, bur oak, black ash, green ash, yellow
birch, basswood, jack oak, pin cherry, ironwood, and tamarack. Of these
only balsam fir, pine, spruce, and sugar maple are sufficiently numerous
to have any importance. Baker (1925) listed Douglas fir, white fir, and
lodgepole pine as the most common associates in the west. Alpine fir,
Engelmann Spruce, and the conifers which seldom form stands, such as
limber’pine and bristle-cone pine, are less frequent associates.

There is quite a number of shrubs, grasses and herbs which are able
to thrive in the aspen understory, particularly in the lighter stands,
but these would be much too numerous to mention if all the sites which

aspen exempts throughout its range were to be embraced.

Succession on aspen lands. It is generally agreed now that the aSpen

 

type is,without exception, a purely temporary one. In a few areas where
Special conditions give it an essentailly subclimax status, a few authori-
ties were formerly prompted to call aspen the permanent or climax type.
weigle and Frothingham (1911) believed that certain stands toward the
northern limit of aspen's range and at high altitudes in the Nest were,
because of their apparently static nature, permanent. They stated un-
qualifiedly that small stands about springs or other moist Spots were
undoubtedly in many cases permanent, and asserted further that in parts
of Alaska and northern Canada could often maintain itself almost indefi-
nitely among the more "shade-intolerant" Species of the far North.
FetheroIf (1917) contended that a strip or belt of aspen existed in the

Rocky Mountains where no native conifer could replace it, because there

was, according to him, no conifer in the district with exactly the same
requirements and qualities as aspen.

Sampson (1916) and Baker (1918) flatly refuted clains of aspen
permanence in the Rocky Mountains. Sampson reported that investigations
in Utah to determine its stability indicated that the aSpen type was a
temporary one, slowly but surely replaced by conifers. He noted, as evi-
dence, aspen's inability to shade out conifers in its understory. Faker
asserted that aspen's apparent permanence in certain areas was just a
case of lack of seed trees, and also cited the fact that conifers generally
seemed to do well when planted under aspen. He admitted, however, that
the seeding in of large areas by conifers was a slow process. Pearson
(l91h) reported that Douglas-fir, white fir and fingelmann spruce thrived
in the shade of aspen, eventually overtOpping it.

Kittredge and Gevorkiantz (1929) found that lack of seed sources and
scarcity of young coniferous growth in aspen stands resulted in prolonging
the aspen association in the Lake States. Only fifteen per cent of the
area of the aspen type was found to be actually in the process of converting
naturally to conifers. Of one and one-third million acres of good spruce
fir-lands which have been replaced by aSpen in the Lake States, Bowman
(l9hb) estimated that only about one-third of a million would likely be
eventually diSpossessed by spruce and fir growing in the understory.
Shirley (19h1) pointed out that there is a number of factors involved
in the scarcity of seed supply. Not only are seed trees few, but they
are poorly distributed, and this obstacle is emphasized by the small

radius of seed distribution of most Species. In addition, seed production

-3 0...

of most Lake States conifers is characteristically irregular. Finally,

a large portion of the seed crop is regularly consumed by birds and
rodents. Shirley concluded that irrespective of other conditions, in-
adequacy of seed supply is destined to prevent natural return of conifers
to aspen lands for many decades.

There is one region where aspen is actually extending its range with-
out the aid of fire or logging. This is in the grassland formation in
Alberta, around the northern and western borders of which there is a
heavy concentration of aspen and balsam poplar in Open, park-like stands,
merging into the boreal forests on the north and Rocky mountain forest
complex on the west. Ross said that the explanation for the advance
of the aspen association is the elimination of fire, the fire apparently
favoring the grasses in this case. Brink and Forstad (19h9) indicated
that they did not consider this sufficient explanation, and speculated
as to whether there might be some significance to the coincidence of the
beginning of this advance and accelerated retreat of the glacier, during
which time the timberline has moved northward.

Mbss claimed that there is evidence that white spruce is the chief
constituent of the climax vegetation over a considerable part of the
region now dominated by aspen and p0p1ar. Yet he claimed that there is
also evidence that aspen is the climax tree of the drier and generally
more southern parts of the region, which seems rather inconsistent, since
there appears to be no logical place in this region to locate the boundary
between permanence and non-permanence of aSpen. Halliday and Brown (l9h3)

attributed the heavy concentration of aSpen around the grassland partly

-31-

to a function of adaptability to climate and lack of competition, but felt
that it might also bear a relation to the repOpulation centers southwest
of the Great lakes; extension of abundance northward might be connected
with the apparent immaturity, post-glacially, of much of the cover there.
Eventually, then, aspen lands will revert to the climax type - if
disturbing influences, such as fire, logging, and grazing, are eliminated.
For practical reasons, however, this can never be completely achieved.
Fires, though much less numerous and rarely as wideSpread as formerly,
will always be more frequent than they were in the virgin forest; logging
will continue, and the ability of the forest manager to influence stand
composition must be reckoned with. Certain Species, such as white pine
and hemlock in the Lake States, have been so drastically reduced in num-
bers that they can hardly regain their former standing. Burning and
erosion have radically changed the site quality of much land, thereby
indefinitely delaying the return to climax vegetation. Seed trees of the
original cover type may have been eliminated from an area so that other
types will take over the land from aspen first, and, in any case, the
change to a climax association may require intermediate steps regardless.
Gates (1930) made a study of the aspen association in Michigan. He
compiled a list of important invaders and their frequency according to
site, estimating how long replacement would take on each site. Fires
are still so frequent on aspen lands that they largely control succession.
Gates found that the frequency, severity of fires, the character of the
stand in which they occur, and the type of site on which they occur all

are important to the progress and direction of succession.

Success in conversion of aSpen lands to other types either by planting
or cutting methods is so difficult to achieve, owing to aspen's aggres-
siveness, that it is of utmost importance for the forest manager to be
thoroughly familiar with the potential natural succession on his lands

and to encourage or plant the species best adapted.

Enemies of fispen and Control heasures

 

Too little is known about the numerous, in fact almost legion,
enemies of aspen to state unequivocally that a particular one is the
most "important." In the first place it is impossitle to evaluate separately
all of the effects of a particular enemy upon the growth and yield of
aspen. Fire, for instance, annually destroys large areas of aspen stands,
but is this loss as great as the reduction in growth and yield from
debilitated soils and the higher incidence of disease in fire-scarred
stands? How much do leaf diseases and insects reduce growth in standing
aspen? Is the volume loss due to mortality caused by canker diseases
greater than the cull produced in standing trees from wood rots? If
boring insects were eliminated from aspen stands, would the amount of ’
disease be materially reduced?

There are no definite answers to any of these questions at present,
and if there were the problem of defining the term ”important” would
still be an obstacle. For example it would have to e decided whether
all aspen stands at large should be included in estimates or whether they
should be confined to aspen under management, and also whether losses

to the recreational and protective values of aSpen cover should he assessed.

Actually, the cuestion is a purely academic one, for the high cost
and low effectiveness of direct control measures make it ridiculous to
contemplate any but the most limited kind of protection for unmanaged
stands. As for managed stands, it is necessary only to know the approxi-
mate importance of the various destructive agents and what practical con-
trol measures can be applied. For these questions there are some answers,

although a great deal remains to be learned.
Diseases

There are no disease or insect epidemics which threaten aspen's
existence, to the chagrin of many foresters, and local epid mics are
Sporadic, and generally unpredictatle. Of greatest concern to the
forest manager is the host of endemic diseases and insects which attack
these short-lived, highly susceptible Species.

ASpen stands tecome decadent so early, even on the test sites, that
the pathological rotation is generally the one which must he adopted in
management. Stand decadence is, in most cases, due primarily to decay.
fieinecke (1929) stated that the risk of infection, as well as the probability
that infection will develOp into decay, is a function of time. he found
that the pathological felling age (point of annual increment decline)
on a site between classes I and II (see Caker, 1925) in Utah was between
eighty and ninety years. In contrast, however, studies in Einnesota
(Schmitz, 1927) revealed that, on average sites, average annual growth
reaches its peak at about fifty years. Allowing for the lag in culr'—
nation of average annual growth behind annual increment, and for the
fact that the site studied in Utah was somewhat above average, this still

points up a difference of about twenty years in pathological rotations.

Baker (1925) observed that growth is more rapid in New England than

in the Rocky Mountains, but that, on the other hand, decay takes place
earlier, so that the maximum and average sizes are about the same in the
two regions and the stands are very similar. ”Whether the greater longevity
of stands in the West is a reflection of a greater resistance to disease

inherent in Populus tremuloides aurea, or of some other factor such as

 

lesser risk of infection in the generally much drier climate of the West,
is not known.

The period of grace, for which cutting may be delayed beyond the
pathological rotation age without serious loss is relatively short.
Stoeckeler (l9b8) estimated about fifteen to twenty years on the best
sites and only about ten on the poorer sites., Because of uncertain markets,
and the poor state of organization of most managed aspen lands, this
constitutes a major cause of loss of volume and of potential income
throughout the range of aspen. Weigle and Frothingham (1911) cited a
case of loss in a Kaine stand described as having been "excellent."
Cutting was delayed for twenty years in this stand and they attributed
an estimated thirty—six per cent loss to the delay.

As indicated above, it has been definitely established that the age
at which stand decadence begins is directly related to site quality. In
the Rocky Mountains, stands may be rendered worthless before they have
reached an age of forty years, whereas aspen will usually live to an
age of 120 years on good sites with little external appearance of de-

terioration (Baker, 1925). Yield studies of aSpen in Wisconsin revealed

~35- '

that cull per cent is higher on poor sites (Anderson, 1936). Poor
site stands in Minnesota may begin to deteriorate rapidly at twenty-five
years of age (Schantz-Hansen, l9h5), while maximum net volume on good
sites in hinnesota is produced between ages fifty and fifty-five
(Zehngraff, l9h7). Stoeckeler (l9h8) found a direct correlation between
pathological rotation ages and soil classes.

'Some evidence has also been presented that the incidence of cull
in individual trees within aSpen stands is related to tree vigor. The
trees on an acre plot in Minnesota were classified according to a recently
recommended system based on vigor, relation to surrounding trees, dominance,
and crown density (Gevorkiantz, 5.12. et a1, 1913). The plot was then
clear-cut and the gross and net volumes recorded, and the figures seemed
to demonstrate clearly that trees with the lowest vigor are the most
defective and slowest growing (Zehngraff, l9h7). Other authorities had
previously expressed the Opinion that some specific diseases of aspen
are related to tree vigor, but this is the first general claim supported
by statistics.

As mentioned before, the number of diseases and insects attacking
aspen is very large. Seymour (1929), for example, listed 133 diseases

as having been reported on Egpulus tremuloides and h8 on Egpulus gran-

 

 

didentata. The number of those which have real economic importance,
however, is relatively limited and many have only one listed occurrence
in the literature, although they may be more common than this would
ordinarily indicate. To mention and attempt to discuss all of these

would be both impractical and pointless, and the following discussion

-36-

is confined to those species which seem to be fairly common or most
severe.

WOod rots. Zehngraff (19L?) declared that wood rot is the greatest
single cause for cull in aspen. meinecke (1929) estimated that an allow-
ance of twenty-one per cent must be made for cull in the West, of which
more than eighteen per cent is due to rot. Schmitz (1927) estimated
that on average sites in Minnesota total rot increases from approximately
fifteen to thirty-one per cent from 30 to 70 years. And an estimate of
nineteen per cent decay in all standing aspen was made by Eaxter (l9b3)o

Three diseases, Fomes igniarius (L.) Gill (including the variety

 

Fomes igniarius nigricans), figmes applanatus (Pers.) wallr., and Armillaria

 

 

 

mellea (Vahl.) Tue1., cause most of the decay in aspen, and of these Fomes
i niarius, or white heart rot, is by far the most important, according

to all authorities. It is found throughout the range of aspen, and

while the canker diseases may be more important in many areas because

of the mortality they cause, Fomes igniarius is apparently always reSpon-

 

sible for the greater portion of decay in standing aspen. As early as

1909, Schrenk and Spaulding reported that Fomes igniarius had been found

 

T'

at such extreme points as maine, western Canada, Oregon, southern New
lexico and Colorado, and there have been many accounts of its preva-
lence and severity since then.

As the common name indicates, Fomes igniarius attacks the heartwood.

 

Trees must usually be old enough to have formed heartwood before infection

is possible, although occasionally the disease will attack "false heartwood"

formed under an Open wound (Spaulding, 1937). Ordinarily, decay is
confined to the heartwood and the older, changing sapwood, but it may
sometimes reach and kill the cambium (Hartley and Hahn, 1920). Rot is
most often centered in the main part of the trunk rather than in the butt
or top, but is not necessarily confined to any particular portion of
the bole (Boyce, l9h8). On the other hand, Horton and Hendee (l93h)
found that it invariably extended farther down than it ran up. Although
the disease itself rarely is lethal to aSpen, the trunk inevitably becomes
broken off by wind when decay is sufficiently advanced.

Three stages of decay are recognized: incipient, intermediate,
and advanced (Schmitz, 1927). Incipient decay is apparently never culled
by wood-using industries, and whether a deduction is made for intermediate
decay depends upon the use to be made of the wood. For those uses such
as excelsior, b0x lumber, low grade construction lumber, and pulpwood this
stage of decay is not serious and therefore generally not culled (Zehngraff,
l9h7). For a few purposes even wood in the final stage of decay is not
rejected, but, obviously, trees cut for lumber or dimension stock must
not show evidence of decay past the incipient stage, since beyond this
point the wood becomes brittle and loses strength. In the past, the
tendency has been to overcull for lack of exact information about the
actual effect of specific stages of decay on utilization for various pur-
poses, but research is correcting this.

Another factor has often been involved in excessive allowance for
cull, this being the scaler's ignorance of the extent of the decay in
stumpage indicated by external signs. Studies have been made which

have partially obviated this difficulty. horton and Hendee (l93h), and

-3 ‘3.-

Riley and Bier (1936) investigated the relation of the fruiting bodies

of the fungus (or sporophores) to the progress of decay. Both concluded
that they were useful in estimating the maximum per cent of cull, and the
latter asserted that log—makers could quickly learn to estimate cull from
them with considerable accuracy. Horton and Hendee stated that fruiting
bodies, if present, give a complete indication of the amount of defect

in a tree or log by their number, size, and distribution. Brown (l93h),
however, contended that while the maximum height of fruiting bodies is
correlated with rot percentage, their number is not. He found that another
measure, rot diameter which may be determined with an increment borer, is
as simple and accurate as any. Hirt and Hopp (l9h2) rendered the age of
fruiting bodies useful by discovering that one tube layer is formed on
them each year, except when their growth is restricted by surrounding
callus or other adverse factors.

Fomes igniarius, as well as the other decays, requires some wound

 

before infection takes place. The chance of infection depends upon the
surface exposed by wounds and the time of exposure, which involves the
character of the wound, and the age and vigor of the tree (Schrenk and
Spaulding, 1909; and heinecke, 1929). Meinecke found that infections
are most common on wounds like fire scars and bruises from falling trees
having large surfaces, or those forming spore traps, like ingrown stubs
and broken tOps with a rough surface of splintered wood. That boring
insects are influential in producing avenues for infection has also been

pointed out (Schmitz, 1927; hegnier, 1932; and Bier, l9hO). Grazing or

-3 9...

browsing animals, where plentiful, often provide ideal conditions for
the spread of fungus diseases by barking trees (Packard, l9h2), and
heavy grazing causes root injury which can admit disease. Schrenk

and Spaulding (1909) decided that climate, character of the surround-
ing forest (except as it does or does not contain the host), and char-
acter of the soil have little or nothing to do with the virulence of

Fomes igniarius.

 

Verrall (1937) said that there seem to be three forms of E9335
1 iarius, one of which is specific to aspen, and thus there is the
possibility that the presence of sporOphores on other species may not
be a serious source of inoculum to aSpen.

Fomes applanatus (Pers.) Wallr. and irmillaria mellea (Vahl.) Duel.

 

 

reSpectively cause white butt rot and shoestring root rot of aspen. Both

are of wide distribution in North America and next to Fomes igniarius

 

these seem to be the most prevalent rots in aSpen, but the literature
presents no reliable estimate as to which is responsible for the greater
amount of decay, nor even what approximate percentage of decay they are

responsible for. Schmitz (1927) said that Fomes igniarius is so prevalent

 

as to usually mask or conceal rot caused by Armillaria mellea and Fomes

 

applanatus. They are definitely less important than Fomes igniarius, how-

 

 

ever, and it is probably safe to estimate that they rarely cause more
than four or five per cent of the decay in aspen stands, and generally
less than that.

Both are commonly present in aSpen stands as saprOphytes and gain
entrance into living aspen through wounds at the base of the tree or on

the roots, caused most frecuently ty fires and grazing. Ermillaria mellea

 

-h 0-

may be present in the roots of healthy trees (Boyce, l9b8), but

is virulent only on trees of poor vigor resulting from unfavorable
environmental conditions, such as drought or poor soil (Baxter, l9h3
and Boyce, 19h8). Rotting of the wood, both heartwood and sapwood,
of the roots and root collar are caused and the death of the tree
follows.

Fomes applanatus is usually present mostly on dead timber,

 

but when afforded an opportunity for entry into live trees through
wounds it will decay the heartwood in the butts, seldom extending
more than two feet up in the bole (Horton and Hendee, 193k), but
sometimes for twelve to fifteen feet or more (Boyce, 19h8). Occa—
sionally it will attack the sapwood and kill the trees when decay
has progressed far enough. 0
Young aSpen stands which are primarily of root sucker origin
often contain a high percentage of defective and diseased stems,
posing the question of whether rot is transmitted through the roots
from the parent trees. Schmitz (1927) could find no evidence that
suckers are infected by the parent stump through the roots. He

reported studies by Ecklund and Wennmark (1925) on the same prob-

lem with Pepulus tremula, however, which led them to believe that

 

Armillaria mellea is transmitted through the roots after a certain

 

number of years. Zehngraff (l9h6) presented evidence that whatever
the reason for the high percentage of diseased suckers enough sound

stems are left to produce well-stocked mature stands.

Cankezs. There are only two widespread canker diseases which

cause serious damage to aspen stands. These are Hypoxylon pguina—

 

Lug (Klotsche) Cke. and Cytospora chrysosperma (Pers.) Tr.

 

fiypoxylon pruinatum is widely distributed from Alberta east to

 

Nova Scotia, and south to Kinnesota and Massachusetts (Boyce, l9h8).
Hartley and Hahn (1920) described a canker disease in Colorado

which is probably fiypoxylon pruinatum. Although first reported in

 

New York (Povah, 1921,) and Raine (Schreiner, 1925), its greatest
prevalence is in the Lake States, and it has been called unquestion-
ably the most serious disease of that region (Christensen, Anderson,
and hodson, 1951). Infection in Wisconsin was found to range from

0 to 53 per cent, with an average of 2b per cent (Gruenhagen, l9h5).
Data from different parts of aspen's principal commercial range in
the eastern United States and Canada indicated that about twenty
per cent of the trees were either infected at the time of investi-
gation, or had been killed by Hypoxylon canker previously (Christen-
sen, Anderson, and Hodson, 1951).

Artificial inoculations and field observations have definitely
demonstrated the disease to be a wound parasite (Bier, 19h0), but
inoculation experiments also suggest that infection takes place
through cuts with difficulty (Gruenhagen, 19h5). Infection occurs
easily through bruised and killed tissue and is commonly associated
with insect punctures, wind breakage, and branch nodes (Bier, l9h0).

The disease does not appear to grow very deeply into the wood, but

is confined mostly to the bark and cambium. If infected below

the crown the trees are girdled and killed, or the trunk may

become so weakened that it is broken off. Small trees may be

killed in two or three years, those up to four inches in diameter

in S to 7 years, and larger trees in 10 to 15 years (Christensen, et
a1., 1951). Bier (l9h0) found cankers on trees of all ages up to
sixty-five years. Trunk cankers were located in the upper part of
the bole in older trees, and since cankers were never found attacking
the thick corky bark in the basal region of older trees Bier con-
cluded that susceptibility is not dependent on the age of the trees,
but on the age of the bark. Be also asserted that incidence of
Hypoxylon canker is not related to individual tree vigor; that trees
of all crown classes are equally liable to infection.

Other observations have in some cases contradicted Bier's
findings, however. Several studies have indicated that smaller and
younger trees are more susceptible, although definite proof is still
lacking (Povah, l92b; Schreiner, 1925; Iorenz and Christensen, 1937;
Gruenhagen, 19h5; and Christensen et a1., 1951). Also, there is
some evidence that vigor does affect susceptibility to some degree.
lorenz and Christensen (1937) found fewer dominant trees infected
than those in lower crown classes. The question of vigor versus
incidence of Hypoxylon is really unsettled and will require further
research.

Zehngraff (19h9) said hypoxvlon appears to increase with stand

density. Investigators in Wisconsin (Gruenhagen, 19h5 and Wilde,

l9h8) and in Minnesota (Zehngraff, 19h?) encountered less disease
on good sites than on poor and medium sites.
Cytospora EthEOS erma, which is the imperfect or conidial

stage of Valsa sordidg Nit., is, like vaoxylon pruinatum, a wound

 

parasite, and most frequently enters through dead twigs and small
branches which die naturally from shading. CytOSpora is much less
virulent, though, becoming parasitiq and killing trees by girdling,
only if the hosts' vigor is definitely reduced by drought, poor site,
frost, or fire. long (1918) reported that aspen growing at the lower
limits of its range is often attacked and the smaller trees killed
outright. In New York vigorously growing trees inoculated with

yalsa sordida either healed the wound or a small canker formed and

 

was healed over. Trees on poor sites died, but some were transplanted
to a site favoring vigorous growth and these apparently recovered and
grew vigorously (Schreiner, 1931a).

It is prevalent throughout the range of aSpen in the United
States, but important only in the western part of the United States,
and the New England area (including New York), (long, 19133 Hubert,
1920; Brown, 1922; Povah, l92h; and Schreiner, 1931b). Even here it
approximates the damage done in the Lake States by Hypoxylon Canker

only under abnormal conditions. Leinecke (1929) described a canker,

 

which he believed to be Cytospora Chrysosperma, as the nest important
bark disease of aspen in Utah, yet estimated that it was responsible

for a cull percentage of only about 2.25. In contrast, Brown (1922)

called Cytospora canker the most serious disease of popla-s
(including aspen) in arizona and characterized it as "very
destructive," and in New York stands weakened by fire had over
sixty-eight per cent infection, with thirty per cent mortality
(Povah, 192b). The disease is a relatively minor one in the
Lake States (Christensen, 19h0), though quite common as a sapro-
phyte.

One or more Species of Eectria causes a canker disease of
aspen. hectria attacks hardwoods generally, and is particularly
abundant in the Lake States and in the northeastern section of
aSpen's range. Factors affecting the severity of Nectria are appar—
ently little understood, but seem to involve both variations in
susceptibility of the tree and environmental conditions. Very
slowly developing target-type cankers are formed which rarely girdle
the tree and are primarily important because they deform the bole
causing trees to be culled, or result in breakage. The fungus
enters through unprotected wounds and small injuries.

There are few specific references to the disease as occurring
on aspen. Lorenz and Christensen (1937) rate the disease as only
"occasional" in the Lake and Central States. A recent report from
the Lake States Forest Experiment Station (Christensen, et a1.,
1951) said Nectria cankers "seldom are common on aspen and when they

do occur rarely kill the tree or eXpose the wood to invasion by

decay fungi..." and "... do not seem at present to be of much

-55-

practical importance.." heinecke (1929) found the disease in Utah,
and losses in a representative stand amounted to a little over
four per cent, due approximately equally to direct losses and to
losses to decav entering the dead wood eXposed by cankers.

A canker disease called Neofabraea populi Thompson has been

 

reported from Ontario (Thompson, 1939). Trees three to six years
old and not over 1.5 inches in diameter are affected. Cankers
are located near the base of the stem and occasionally kill the
trees.

leaf diseases. leaf diseases are not important enough to be

 

considered a factor affecting the management of aspen. Individual
leaf diseases periodically become epidemic locally but few cause
more than a temporary slowdown of growth. It has been suggested

in one instance that the aggregate effect of leaf diseases cause
early deterioration of poplar stands on burned-over areas and aban-
doned farm lands in the East, but no evidence of this was produced
(Cornell Station Report, l93b).

Napicladium tremulae (Frank) Sacc. causes twig blight of

 

aspen, a drying out and death of young shoots and leaves during
the summer. thallum (1920) first reported its presence in North
America in 1920 and found it common in Quebec and Ontario. lorenz
and Christensen (1937) found it associated with the dying of the
leaves and leaders of young aspen reproduction throughout the Lake
States. Christensen et a1 (1951) said it occurs from Maine to

Minnesota, and that it is of wide distribution in aspen suckers,

-16-

but doubted that young sucker stands are excessively damaged by

it. harssonia oopuli (Lib.) Sacc. is an anthracnose of poplars

 

which kills small lateral twigs of aSpen and the portion of the
main stem where these twigs join it (Halsted, 1897), and may
ruin trees in the advanced stage. It is widespread, but most
prevalent in the southern Rocky Mountain region (Boyce, 19h8).

Sclerotinia'flhetzellii Seaver and Sclerotinia bifrons Seaver

 

 

and Shope cause ink spot disease of aspen leaves which are common
in the East and West, respectively (Seaver, l9h5). The disease
produces black sclerotia on the leaves during the summer which
drop out, leaving holes in the leaves; severelv infected leaves
die, and sometimes small trees are killed. Ink spot disease is
present in endemic form throughout most of the United States and
Canada, affecting only quaking aspen. Hartley and Hahn (1920)

considered Sclerotinia bifrons to be the most important leaf disease

 

in the Pike's peak region of Colorado, but only one severe outbreak
of the disease over a large area has occurred, that being in Quebec,
neighboring provinces, and adjacent parts of the United States
(Pomerleau, l9hO). Pomerleau reported that phenological observations
indicate the fungus prefers fairly cold climates and requires a
rarely occurring combination of climatic factors to become epidemic.

Septoria musiva Pk. and Septoria pppulicola cause necrotic lesions

 

 

on the leaves of various p0p1ars throughout the United States and
Canada (Thompson, l9hl). Inoculations prove aSpen's susceptibility,

but no serious damage resulting from these diseases has been recorded.

-71}, 7 ..

A leaf rust, Ielamgsora albertensis Arth., is common on aSpen

 

in the West, but of minor importance (Jackson, 1917; Hartley and
Hahn, 1920; and Xeinecke, 1929). Douglas-fir is the alternate host

of this rust. A powdery mildew, Uncinula salicis (Fr.) Wint., is

 

common on aspen in the Southwest (Lainecke, 1929), but of no conse-

quence.
Insects

As a group, insects probably cause greater loss indirectly, by
reducing tree vigor and growth rate, and hy carrying disease and
’providing avenues of infection, than as a result of direct physical
injury. Periodically, some of aspen's insect enemies become epi-
demic, and temporarily over localized areas cause damage exceeding
that resulting from disease or other enemies. Generally speaking,
however, insects are not reSponsible for extensive cull or high
mortality.

Two insects have proved to be primary destructive agents
of aspen. One of these, and probably the most important, is the

forest tent caterpillar, halacosoma disstria Hen., which is a de-

 

foliator. Records show that outbreaks of this insect have been
occurring at more or less regular intervals of ten years for at
least one hundred fifty years ( aird, 1917). They occur simul-
taneously in a number of widely scattered areas throughout the
lnited States and Canada, and, to judge from the most recent epi-
demics, may be increasing in duration and extent in response to the
tremendous expansion of the aspen type, the preferred food of the

forest tent caterpillar (Christensen et a1., 1951).

.413-

The most serious depradations during the last two outbreaks,
as far as is known, have been inflicted in the Lake States. Several
surveys following the first of these found from twenty to eighty
per cent of the trees dead, the degree of damage depending upon the
site, number of complete defoliations, and age of the trees. The
last outbreak is currently in progress, having begun in l9h9 at
the eastern end of the Upper Peninsula of Michigan, and appears to
be at least as severe as the previous one. Epidemics are terminated
naturally after several years by a number of environmental factors,
among which Spring fronts, high summer temperature, parasites, disease,
and starvation are known to be operative. (Hodson, l9bl). Between
outbreaks populations are very low.

The other important insect of aspen is the common p0p1ar borer,

Saperda calcarata Say. This wood borer mines in the bark, sapwood,

 

and heartwood, excavating galleries which may exceed a foot in length.
Trees attacked severely by the poplar, and there is a tendency for

the insects to concentrate on those previously attacked, producing
so-called "brood trees" (Hofer, 1920), are greatly reduced in ouality
and may be weakened to the point of subsequent breakage. Study of
affected trees showed that one of the reasons for the rapid deteriora-
tion of many attacked trees is heart rot which rapidly penetrates

the Opening made by the insect; other insects too are commonly asso-

ciated with poplar borer injury (Hofer, 1920). POplar borer is very

widespread (Chrystal, 1919), but is not given to extreme pOpulation

gradations as is the forest tent caterpillar, being an ever-
present source of injury in aspen stands.

Hofer (1920) contended that the poplar borer attacks only
trees from two inches up, larger ones often close to the limbs and
the smaller ones from the base up, but later investigations have
found the borer attacking trees as small as one inch in diameter
(Christensen et a1., 1951). In Saskatchewan Peterson (l9h8) found
evidence that density of stands has a direct influence on the pattern
of borer infestations, the latter being concentrated around the
margins of stands and only penetrating into them.where the trees
are scattered. A survey in hinnesota during 19b? revealed a strong
predilection of the borer for stands on poor sites (Christensen et
a1., 1951). Infertility, climate, excessive Sap flow, parasites,
disease, woodpeckers, and unsuitable or insufficient food all con-
tribute to keeping the p0p1ar borer in check (Peterson, 19L8).

A number of other leaf—feeding and wood boring insects may
attack aspen, most of which cause serious damage only occasionally

or locally if at all. Agrilus liragus is a borer commonly found on

 

weakened and dying aspen. The flat-headed wood borer, Poecilonata

 

cyanipes Say, often deposits its egg masses in the scars of the aspen
borer and in axe marks and bruises, and extends its damage to the

heartwood. Electrodera scalator Fabr., the cottonwood borer, has

 

been observed attacking younger aspen in the Lake States. It
is always found near the ground line and the larval mines extend

some distance below the ground into the roots. Sagerda concolor

 

lec., poplar-gall saperda, and Saperda moesta Lec., pOpIar—twig

 

borer breed in the branches of aspen causing galls with ultimate

death of the branch. A carpenter moth, Prionoxystus rodiniae Peck,

 

is prevalent on aspen in certain areas of the Lake States, and a
different Species in the Southwest is found in trees infested by
the poplar borer. The larvae of the carpenter moth burrow in the

wood of the trunk. A round-headed borer, Xylotrechus oblileratus

 

lec., has been described as a chief predator of aSpen in the South-
west. The flat—headed larvae of one or more species of the genus
Dicerca are common secondary invaders of dying and dead aspen.

Cryptorhynchus lapathi L” poplar and willow borer, occasionally

 

attacks isolated trees killing small branches and twigs. Carpenter

ants, Campanotus herculeanus L., freouently take over old larval

 

galleries and extend the damage.
A variety of beetles are common defoliators of aspen trees.

Among these are the leaf beetles, Chrvsomela scripts Fabr. and

 

Chrysomela tremulae Fabr.; the American poplar beetle, Phytodecta

 

 

americana Kby.; and the curculionid beetles, Tricolepis inornata horn,

 

in the Southwest. Occasional outbreaks of the large aspen tortrix,

Archips conflictana walker, in Canada and the Lake States, and the

 

early aspen-leaf curler, EroteOpteryx oregona'Wlshm., in Canada have

 

defoliated considerable areas of aSpen. The white marked tussock

moth, Hemerocampa leucostigma S. and A., and the gypsy moth, Porthetria

 

 

diSpar L., sometimes attack aSpen, although it is not a preferred
host. Isolated aspen trees are sometimes stripped by the poplar saw-

fly, Trichiocampus viminalis.

 

Animals

Aspen has an important place in the diet of many animals throughout
its range, frOm both choice and necessity. Except for the beaver, few
of these animals kill older trees directly, and beaver damage is limited.
where animals feeding on aspen become concentrated, however, aspen repro~
duction is seriously limited and sometimes virtually eliminated, at least
temporarily. A secondary but important influence is the increased sus-
ceptibility of stands to insect and disease attack caused by injuries
and retardation of growth.

Grazing and large browsing animals cause the greatest destruc-
tion. Tallies of reproduction killed or injured in Utah (Sampson,

1919) by sheep averaged approximately 32 and 65 per cent respectively
for lightly and heavily grazed plots. Corresponding destruction

by cattle grazing was slightly less than half that from sheep, but,
on the other hand, cattle browse higher on the stems so that seed-
lings must be four to five years old before they are exempt from
serious damage, in contrast to about three years for sheep. Pearson
(lSlh) blamed grazing for keeping down suckers for many years in
sections of Arizona and New hexico. Curtis (19h8) reported that no
aspen reproduction of any consequence occurs where sheep and cattle
graze in Utah. Bark injury is heavy in the winter elk range of the
West (Packard, l9h2).

Aspen is not a preferred food Species for deer. hill (l9hé)
reported that deer in the :lack Hills eat little or no aspen except

during April through June, and Swift (l9h6) listed it as a poor

second choice or even starvation winter food. In spite of this, in
areas where pOpulations become too heavy for the normal food supply,
as is currently the case in the Lake States, there is heavy usage of
aSpen twigs and Sprouts for winter forage. A recent survey in his-
consin showed that LG to 50 per cent of the aspen in the northern
and central portions of that state had been damaged. Aspen can
withstand a single heavy winter browse, however, and come back with
a heavy crop of sprouts the following year. Contrariwise, moose
exhibit a high preference for aspen as a winter browse (Aldous

and Krefting, l9h6), but rarely attain a high enough population
concentration to cause extensive damage. when populations do become
high, as on Isle Royale, Michigan, they bark and often kill standing
trees (Krefting and Lee, l9h3). .

Aspen is the favorite food species of beaver, and is used also
for building dams and lodges. Leaver will forage as far as four
hundred feet or more from the shores of rivers and streams, and will
cut trees up to eleven inches in diameter, although their preference
is for those about two inches in diameter (Bradt, 19h7). The bark
of most trees up to three inches in diameter is completely utilized
for food, but beavers out many larger trees which are wasted because
they lodge in other trees, are too unwieldy, or are not considered
palatable. One study measured a waste of sixty-four per cent (Aldous,
1938). An acre of aspen will support an average colony of five
beavers for from 1 to 2.5 vears, depending on the character of the
stand and other factors (Brait, l9h7). When the available food
supply at their home site is exhausted, the beavers migrate to a new

location.

-53-

The snowshoe hare feeds on aspen Sprouts and will sometimes girdle
small trees. A survey reported by Christensen et al. (1951) revealed
that five to ten per cent of the aspen reproduction in northern His-
consin had been browsed by hares. Bird (1930) alleged that in the park-
land region of Alberta aspen would advance much more quickly onto the
prairie if it were not for the rabbits. Other animals known to feed on
aspen to some extent include red squirrels, black bears, porcupines,
goats, gophers, bighorn sheep, mule deer, and field mice.

Aspen is one of the staple foods of ruffed grouse the year around.
leaf buds, catkins, flower buds, and leaves are all eaten during various
seasons. Feeding is most intensive during the spring, and buds are the

most important part eaten (Edminster, 19b7). Two species of sapsuckers

seriously scar trees by drilling.
Fire

While fire is a great aid to the establishment of aspen stands it
should not be inferred that burning after aspen is established is bene-
ficial. To the contrary, fire is very destructive to standing aspen.

These thin-barked species are easily killed by fire, and all fires, whether
light or heavy, invariably reduce growth, cause fire scars which admit
disease, and deteriorate the site.

If fires are too frequent, particularly when they are annual, aspen
is likely to be destroyed completely, and a meadow of grasses develOps
(Gates, 1930). Pearson (l9lh) expressed the opinion that repeated

fires had undoubtedly in some instances entirely exterminated aspens

in Southwestern areas, despite its great cagacity for propagation
by root suckers. Numerous investigators have further attested to
Vthe connection between fire injury and decay. Leinecke (1929)
rated fire wounds as the most important factor in the spreading of
disease in aspen. Stoeckeler (l9h8) investigated especially the
relation between fire and lowering of site ouality, which may amount
to a reduction of seventeen feet in site index from a single fire of
moderate severity. Found contributing to this deterioration were
consumption of the litter, F, and H layers of the soil, thus destroy-
ing much of the vast network of fine feeding rootlets in the lower
portions of the organic layer; loss of nitrogen for tree growth; and
decreased infiltration and water holding capacity.

Rigid fire protection is therefore an absolute necessity in
management, and it is to be expected that with it aspen sites should

gradually rejuvenate themselves.
Clinatic factors

Aspen is well adapted to climate within its range, but severe weather
sometimes causes considerable damage. 'Hindstorms occasionally cause break-
age and some windfall over extensive areas, especially of trees weakened
by decay. RSpen is one of the more susceptible trees to glaze injury (Fax-
ter, 19h3) and hail bruises admit infection.

Drought very definitely lowers the vigor and growth rate of
trees, predisposing them to insect and disease injury. Aspen is
relatively susceptible to sunscald of the holes from direct sunlight,

particularly after excessive thinning of stands (Bickerstaff, l9h6,

-55..

and Zehngraff, l9h9). high temperatures are extremely lethal to

aspen seedlings. Frost, on the other hand, retards or kills many aspen
sprouts (Baker, 1925), taking a high toll of those originating after fire
or logging during the growing season, or not appearing until the third

year after removal of the crown canopy.
Protective heasures

The prevailing low value of aspen timber, because of poor quality
and limited demand, militates against elaborate and costly control
measures. The cost of most artificial or direct control measures for
diseases and insects is almost completely prohibitive. Utilization stan-
dards are relatively low for most products into which aspen is converted,
and indirect methods of control are usually the most effective for keeping
loss at a reasona‘le level efficiently.

The forest service declared recently that, "in the long run, healthy,
growing forests, well-suited to the site and able to resist attack, will
be the best defense against most insects and diseases, and more attention
should be given to testing and applying the indirect methods of control."
(U.S.D.A., Forest Service, 19h7). Indirect control refers to the modifi-
cation of forest conditions, through silvicultural and forest management
practices, designed to make them less favorable for insect and disease
outbreaks.

Direct controls are justifiable only for the prevention of

fire and animal damage. Fire is probably still reSponsible for

the greatest amount of destruction to aspen. Furthermore, it is
the major introducing agent of disease and seriously reduces growth
and vigor, thereby increasing the degree of loss from both diseases
and insects. Consequently, fire protection is the most important,
single control measure to be applied to aspen stands, and is, in
fact, the only active protective measure in force over most of the
aspen acreage today. The first step taken in putting any aspen land
under organized management should be increased fire protection, if
only to reduce the risk of carrying stands to maturity.

The problem of controlling animal damage is an important
one in the nest where a good part of the aspen type is used as range—
land for domestic cattle and sheep. Grazing on these lands should ,
be strictly regulated, and is on the national forests. Sampson (1919)
recommended that sheep be completely excluded for three years follow-
ing cutting to guarantee establishment of full stands, though light
cattle grazing is permissible. In stands being managed primarily
for timber production, anywhere, grazing should be strictly prohibited.
It has been suggested that regulated grazing may help growth of
young stands by reducing competition, but the benefits, which are
subject to doubt, hardly seem to warrant the cost of supervision and
the risk of introducing excessive decay.

In regions where browsing animals are too numerous game control
laws should be revised to reduce their pOpulations in the states con-

cerned. Small animals, such as rabbits and rodents, may sometimes

-57-

need to be trapped or poisoned on areas of young growth which are
particularly subject to injury.

When extensive management is practised, maximum net volume
production is best assured by selection of the proper rotation age
according to site ouality, since the rate of decay rapidly increases
with age. Removal of the overhead canopy in logging must be as
complete as possible, for leaving standing cull trees, or trees
below the merchantable diameter limit as in "diameter—limit" cutting,
invariably suppresses young growth and favors invasion of the site
by brush species which compete for water and nutrients. Trees which
cannot be felled should be girdled or poisoned.

Intensive management practices must be concentrated on the
better sites. It has been demonstrated that on such sites aspen
responds well to thinnings (Zehngraff, l?h7). The most important
effect of thinnings is a shortening of the rotation by as much as
five or ten years if properly applied, allO"ing the stand to be
removed before extensive decay can set in. By proper thinning
procedures growth can be concentrated on selected, vigorous, healthy,
well—formed crop trees, thus maintaining maximum resistance to in-

sect and disease injury. Since stung-s;

arouts and root collar Sprouts
are poor risks these shotld Le discriminated against, while seed-
lings should be favarel when tley are distinguishable. Tlinnings

can and do partially serve the functions of salvage and x'nitftion

cuttings by removing trees which have succumbed to insect or disease

attack, or appear to be poor risks.

It is important for reproduction cuttings to be made during
the dormant season to ensure prompt sprouting and full stocking.
Needless to say, care should be taken to avoid injury to standing

trees in all logging and road-building operations.
Growth and Yield

Ey the nature of their usual origin because of the Species'
extreme intolerance most aspen stands are naturally very even-
aged. ispen reproduction in thrifty stands is are, although
fires may open up stands sufficiently to admit new growth, giving
them a two-aged form. As the stands decline and break up after
maturity, the new growth may be relatively uneven-aged for several
years, but tends toward even-aged form later on.

Under Optimum conditions for reproduction, which is most com—
monly of sucker origin, extremely dense aspen stands originate.
Tallies of Sprouts on completely clearcut sites in Utah totaled
as high as h0,000 per acre ( aker, 1925). Clearcuttings during
the dormant season in Minnesota produced from 6,100 to 22,850
stems per acre within one to three years following cutting. (Zehn—
graff, l9h6a). Initial stocking varies widely, of course, with
changes in the factors controlling reproduction. For example, in
contrast to the h0,000 sprouts per acre produced on clearcut areas
in Utah, mentioned above, only 2,73h Sprouts to the acre were pro-

duced when a residual stand admitting only 0.5 to 0.6 full sunlight

was left. Natural mortality is very high in young stands, due
to intense competition for light, water, and nutrients, and at

twenty years of age in the Lake States only atout l700 stemsfmifg

,.-.- s._,.,

the acre remain on the best sites and aboutf2000 on poor sites. 3

—.
x»~__‘-._—-~ -—--- —. _ _, .‘_ __

These numbers are reduced to approximately 330 and LZO, respectively,
at the age of sixty years (Anderson, 1936). Zehngraff (l9h7a)
recommended that the number of trees be cut to between 200 and

250 per acre on good sites by age forty to forty-five for maxi-

mum growth in managed stands. The small number of stems remaining
in mature aspen stands points up the fact that the most serious
result of imprOper cutting practices is not reduced reproduction

222 fig, but rather the pernicious effects which they have on

ensuing reproduction.

Incomplete cutting, and cutting during the growing season
particularly, delay reproduction and cause sprouts to be less
vigorous and slower growing. The poorly stocked young stands are
easily invaded by brush and weeds which further inhibit growth, and
are more susceptible to both animate and inanimate injurious agen-
cies. Surviving trees have poor form and quality and stand deca-
dence is hastened. Weigle and Frothingham (1911) found that a
sufficient number of thrifty, dominant sprouts for a pure stand
of aspen remained nine years after cutting only when the density
of the crown cover was no greater than 0.1. Thus the yields in

poorly managed stands are invariably lower, and the risk of carrying

.60-

them to a given age is increased.

Data on the rate of growth of stands less than twenty years
of age is limited, but averages approximately 2 to 3 feet in
height per year, not being as dependent on site differences as
is mature growth (Weigle and Frothingham, 1911; Kittredge and
Gevorkiantz, 1929; Tunstell, l9b5). This does not apply to stands
in the Rocky'tountains, for here young Sprouts average only Slightly
over one foot in height increment per year even on the best sites
(Baker, 1925). These growth rates, combined with the prompt in-
ception of root sucker growth after fire or logging, enable aSpen
to easily overtOp any competitors, and not until the growth rate
has slackened with the approach of maturity, at the earliest, can
other Species overtake and replace aspen. Gates (1930) found that
replacement requires a longer period of time on Sandy pine soils
than on the better hardwood soils, and that fires as often as once
in twelve years favor aspen at the expense of the pines. Baker (1925)
reported that of the conifers associated with aspen in the Rocky
kountains only Alpine fir is capable of equalling the growth of
aspen during the average life of a stand. The height growth of
seedlings is not as rapid as that of sprouts for about the first
twenty years, but when seedlings become successfully established
in large numbers on bare areas they completely dominate the site
as do stands of sprout origin. neigle and Erothingham (1911)
assumed that aspen seedlings are longer-lived than sprouts in

conformance with the general rule for seedling and sprout growth,

-6 l-

but no experimental evidence is available to confirm this.
Seedlings which happen to start within stands composed primarily
of root suckers, however, usually lose out in the struggle for
dominance.

Height growth falls off markedly on good sites in the Lake
States after 50 years, but diameter growth declines little up to
ages of 70 and 80 years. Eecause of sustained diameter increment
unmanaged stands on good sites continue to add volume until losses
due to natural mortality balance stand growth between 55 and 60
years (Lake States Forest hxperiment Station, l9h8a). deductions
for decay set the age of maximum net merchantable volume at be-
tween 50 and 55 years.

The dominant trees in unmanaged stands do not generally ex-
ceed 10 inches d.b.h. and seventy-five feet in height at the age
of maximum yield (Anderson, 1936; Zehngraff, 1927a). While in-
dividual trees may reach diameters of 12 to 16 inches d.b.h. and
heights of 80 to 90 feet if left to grow until seventy to eighty»
years old, stands are heavily deteriorated by that time, and at
ninety years exist only as scattered cull trees.

DevelOpment of poor Site stands isstrikingly inferior to that of
stands on good sites. height growth is most seriously affected,
diameter growth somewhat less. Stoeckeler (19h8) calculated that
maximum net merchantable volume in cubic feet was reached at hS years

or less on low ouality soils. on the poorest sites, termed "off

-c‘~2-

sites," aspen has a scrubby form, and yields practically no mer-
chantable material under normal utilization standards, although
Schantz-Hansen (19b5) showed that stands situated very close to
wood-conversion plants using small-size pulpwood can yield a
profit. Poor site stands generally become decadent before they
reach the age of fifty years, at which enough trees would other-
wise attain the size necessary for appreciable pulpwood yields.
Cordwood for fuel, excelsior, etc. is usually the only product,
and it may have to be harvested before stands are 35 years old.

Populus grandidentata is reported to reach optimum growth at

 

an earlier age and size than Populus tremuloides, which would in-

 

dicate shorter rotations in areas where stands are predominantxy
composed of this species, notably in part of Linnesota (hobinove
and Horton, 1929).

Except for the Rocky Lountains, aSpen yield tables have been
constructed only for the Lake States, but they very probably are
all applicable, within the limits of accuracy they possess, to
southern Canada and northeastern United States as well. Kittredge
and Gevorkiantz published the first set of yield tables for well
stocked Lake States stands in 1929. Tables were prepared for
yields in total cubic feet, board feet by both Scribner Decimal C
and International log rules, and cordwood. Kields were classified
according to five 10 foot site index classes from LO to 80. In

a publication by Johnson, Kittredge and Schmitz (1935) the tables

~63-

for volumes in board feet and cordwood were partially repro-
duced (see Tables 1, 2, and 3 in Appendix). The yields for site
indices hO and 80 were drOpped from the tables and the site in-
dex classes 50, 60, and 70 were simply labelled poor, medium, and
good. These changes in form were probably partly for the reason
that the large majority of sites in the Lake States fall into

one of the three classes retained, and partly in realization of
the fact that on a practical scale five classes were both un-
necessary and difficult to distinguish. Identification of these
site classes was later simplified by relating them to original
cover which can usually be ascertained easiLy (Lake States borest
experiment btation, l935d). The highest ouality class is des-
cribed as aspen of fresh or moist soils originally occupied by
hardwoods or white Spruce, pure or in mixture with white pine or
balsam fir. hedium site aspen is on fresh soils originally occu-
pied by Norway pine and white pine with some hardwoods of inferior
quality. Poor sites consist of dry sands capable of supporting
jack pine and inferior Norway pine, sometimes interspersed with
an undergrowth and mixture of scrub oak.

The tables show possible vields of 37 peeled cords or 6,600
board feet per acre (by the more conservative Scribner decimal C
log rule) on poor sites, whereas forest surveys made shortly af-
ter their preparation found that typical volumes even on medium

sites were only 3000 to 5000 board feet per acre (Anderson, 1936).

Actual volumes in natural aspen stands fall so consistently and
so far behind the normal yield tables that Anderson concluded that
"the usefulness of the latter is brought into question." seasons

advanced for the sreat discrepancies were: (1) existence of fewer

merchantable trees per acre in the typical aspen stand than shown
in the normal yield tables (particularly if cull trees are omitted),
(2) lower average volume per tree in forest stand than in a well-
stocked stand because of poorer form, (3) volume of average forest
tree is less on account of crooks, rot, and other defects, and

(h) more exacting standards of utilization current at the time of
the survey with respect to top diameter and minimum size of mer-
chantable trees. Zehngraff(l9h7a) attributed the over—estimates
to failure to accredit preper weight to: (a) the exceptionally
high natural mortality rate of the species; (b) the high cull per-
centage, especially in older stands; and (c) the natural slowdown
in growth with age.

The largest source of error is undoubtedly the high propor-
tion of aspen lands which are under—stocked. flecent figures from
the forest survey in the Lake States revealed that of the nearly
twenty million acres of aspen type, almost five million acres, or
a quarter of the total, are poorly stocked or denuded (Cunningham,
et al., 19h6). Early survey data disclosed that whereas normal
aSpen stands at sixty years of age are supposed to have from 330

trees per acre on hardwood land to h22 trees per acre on pine land,

the actual numbers of sound trees in average stands were only 215
and 110, respectively (Anderson, 1936). Lot only were there fewer
merchantable trees, but the open-grown trees were shorter and of
poorer form, and consequently contained less merchantable volume.
According to the yield tables a lb" tree from a well—stocked stand
contains about 170 board feet, yet trees of the same diameter in
under-stocked stands contained only about 110 board feet.

Survey figures on merchantable volume were in general agree-
ment with those of Schmitz and Jackson (1927), although showing
considerable variation with site and product. A later study of
heart rot in Canada in which the figures for all sites were
grouped tOgether found an extraordinarily high rate of decay
amounting to 50 per cent defective or cull volume between 70 and
80 years of age. hlthough these figures are not applicable to
the lake States, and are not specific enough for general appli-
cation in any case, they serve to emphasize the important role
of decay in determining yields in unmanaged stands.

'A yield table constructed from early forest survey data,
Anderson (1936),. (see Table h in Appendix) gives empirical
yields in both gross and net volumes under the forest survey stan-
dards of utilization in force at that time. The site classifi-
cation adopted corresponds fairly closely to the system used by
Johnson, kittredge, and Schmitz (1930). fhe sites were defined

by the natural cover type and heights were omitted, apparently

because of the reduced correlation between site product‘vity and
site index in under-stocked stands. Yields are revised downward
drastically from those given in the previous tables, but, strangely,
follow the same trend of continued merchantable volume increase
with age even during overmaturity. It seems extremely doubtful
whether the figures for at least the 70- and 30—year age classes
can be considered valid.

The most recent yield table for the lake States, published by
Zehngraff (1947a) izee Table 5 in Appendix), agrees with the recog-
nized form of volume-over-age curves, showing maximum yields at

In

between 50 and 55 years. The yield figures represent the gross

volume which may be expected in well-stocked,(unmanaged stands.
Sufficiently detailed information on the relation of cull to age
on various sites in well-stocked stands was not available for
close estimation of theoretical net merchantable yields. Stoeckeler
(l9h3) has constructed a set of vield curves, however, for five
soil classes corresponding to the site—index classes of hittredge
and bevorkiantz (1929), which show empirical merchantable vields
in cubic feet and cordwood from investigations in linnesota and
hisconsin.

Baker (1925) composed an empirical yield table for aSpen in
the Central ice I Lountain region which sets forth gross yields in

cordwood and board feet. It is meaningless to compare yields on

a given site in this region with yields on sites of coordinate

ouality in the lake btates because the growth rate of aspen in
the former region is much lower on all sites considered collec-
tively. Obviously, therefore, productivity is correSpondingly
higher in the Lake States. an the other hand, if the stricter
standards of utilization adopted in the greparation of baker's
table are taken into consideration it appears that final yields may
equal those of the Lake States. This is because the rate of
volume increment does not fall off until ages of 80-90 years due
to greater stand longevity (Leinecke, 1929), by which time indi-
vidual trees are approximately as large as those in mature stands
of the Lake States.

Accurate prediction of yields under ma agement is impossible
at present, but it seems certain that some increase can be achieved
simply from the increased stocking which preper management can
effect. In addition, experimental evidence gives high promise of
increased yields, improved quality, and shortened rotations under

intensive management on good sites

’ 1' .‘ ,.‘ ".“J '4- .‘ : 1;: L171":
4.xkl‘._M.J._u.Llul \J Aul 1.2m "LIMJQ

Aspen Supply and Ltilization

Acreages and volunes. The entire stand of aspen saw timber

 

in the United States has been estimated verr roughly at 2,3J0,000,000

board feet, in addition to MhiCh there are probably about b0,000,000

cords of wood suitable for fuelwood and pulpwood (Eetts, l9hh).

In the region of Canada made up of the provinces of hova Scotia,

flew Brunswick, Quebec, Lntario, and Aanitoba, the volume of pop-

lar (including aspen and balsam p0p1ar) was estimated at approxi-

mately 2,661,000,003 board feet and 53,357,000 cords (Craiz, 1937).
The stands of commercial aspen saw timber in the tnited States

are located principally in the Lake States and the northeast, par-

ticularly in the former region. The combined stand of aSpen,

cottonwood and balsam poplar of saw timber size in the eastern

part of the United States was placed at approximately 80,000,000,000

board feet in 1938 (t.3. Senate, l9h1). In the Central hooky

Lountain negion (Colorado, Idaho, Nevada, New 4exico, Utah, and

wyoming) Eaker (1925) estimated the stand of aspen at 12,658,000

cords on h,000,000 acres. A survey made in the Iacific Lorthwest

during 1930, by the Pacific horthmest Forest LXperiment Station

as a part of the forest survey of the United States, showed less

than 5,000,000 board feet of saw timber and about 30,000 cords of

pulpwood in Hashington and Oregon.

As yet, detailed statistics on the areas by site class,

volumes by size class, growth, etc. have been published only for
the Lake States. Here, up to date information obtained from the
193h-36 survey, re-evaluated in l9h5, has recently been complied
and published (Cunningham et al., 19L5; Chase, 19h7; Porn, l9h9;
and E.S.3.A., Forest Service, 1950).
The aspen type (lands on which "aSpen ani paper birch, either

singly or torether, make up more than 50 per cent of the stand"
were arbitrarily classified as aspen type. ”Aspen,” in the sur-

vey, included Pepulus halsomifera L., and Iowulus detloides larsh.

 

as well as the true aSpens; lepulus tremuloides was estimated to

 

make up about 50 to 90 per cent of the volume.) occupies 19,853,000
acres or 39 per cent of the commercial forest area in the lake
States. This is slightly more than twice the area of the next
largest type, the northern hardwoods. of the total aspen acreape,
over half is to be found on sites of medium ouality (site index
60-70), with one—third on poor sites (site index 59 or less)
and one-sixth in the good site classification (site index 68 or
greater). Approximately 2h per cent of the aspen tyne falls in
the merchantable pole and saw timber size classes, nearly 2/3
being in the pole timber class. About 52 per cent is considered
as satisfactorily restocking to seedlings and saplings, while an
area a little greater than that hearing merchantable timber is so
poorly stocked as to be practically deforested.

As of l9h5, aSpen constituted 13 per cent of the saw timber

volume (Volume measurements included all ropulus Species, but not

.—

paper birch) of all tree Species in the lake btatss. Ibis eeuals
approximately 6 1/3 billion board feet (by International g—inch
rule), of which 70 per cent occurred in saw timber size stands,
the balance being scattered through pole size and unmerchantable
stands. The actual, usable saw timber volume, however, after dis-
counting for inaccessibility, rot, and loss resulting from over-
maturity was almost 20 per cent smaller. in contrast to the rela-
tively low aspen saw timber supply, the total volume of aSpen
pulpwood was nearly as great as the collective total of all other
common pulping species combined, amounting to 17,300,000 cords of
standard pulpwood exclusive of saw log material. In addition, if
standards were lowered to permit the pulping of all aSpen sticks
over h inches d.i.b. with less than 50 per cent defect, the
utilizable volume would be increased by more than 25 million cords.

Although the total volume of aspen in the Lake itates is
very large, it is not all available for cutting at any given
time. It was estimated that only about one-half of the saw timber
size material and three—fourths of the total cordwood volume
(including standard and sub—standard pulpwood and pulpwood in saw
log material) is in stands with sufficient volume per acre to
permit economic lOgging operations.

on the other hand, growth between 1935 and l9hh was far in
excess of drain due to cutting and all natural losses, and the

margin is eXpected to increase even more in the future. Growth

-71-

for the ten year period lCBh-hh was four times greater in cubic
feet and 2; times greater in hoard feet than drain. Ingrowth of
aspen into the merchantable classes will be comparatively slow
until 1965 when, with continued and improved fire protection, the
vast areas of restocking aspen lands will ”come of age." lt was
estimated that total cut for the region could, without over—
cutting, be increased almost three times, and the saw timber out
about twice, before 1960, and increased thereafter. estimated
allowable annual cuts of saw timber for the period l9h5-l959 and of
pulpwood for the period l9h6-l965 are 300 million board feet

_(International % inch rule) and 2,0h0,000 cords reapectively.
Obstacles to Utilization

Aspen was used only in small quantities until the large
demand for lumber during the war literally forced its use, prin-
cipally in the lake States. Limited demand has been primarily
due to the small size lumber yielded. On many sites aSpen never
attains saw 103 size, and previous to the war trade prejudice and
supplies of larger, higher quality timber species limited cutting
of aspen. Combined with low stand density and high cull percen-
tage, small size still restricts most aspen logging to Operation on
a small, narrow margin scale (Garland, 19h? and Zasada and Kleunder,
19h9). Jith the long established logging and sawmilling methods

set up to handle larger species, like the northern hardwoods,

-72-

costs are high for the small-sized aspen logs obtainrble and are
increased by the uncertain availability of operable supplies of
merchantable timber in many areas, due to irregularity of aspen
stands and the mixed pattern of ownership.

The increased utilization of aspen during the war has led
to studies aimed at finding more economical and efficient har-
vesting methods.' Lechanical equipment, such as power saws, mo—
bile pulpwood harvesters, loading machines, and mechanical barkers
and peelers, has been deveIOped, but most of it is still in the
eXFerimental stage (Schantz-Hansen, l9h8). tome of these machines
have demonstrated their efficiency, but the expense of powered
equipment requires a large operation in valuable timber, which
indicates that its use will generally be precluded for medium and
low quality aspen stands. Of particular interest to growers of
pulpwood stands are methods of artificial peeling, because they
can lead to a wider market and higher prices while allowing cut-
ting during the dormant season. Various systems of bucking,
skidding, and_bunching and of manpower disposition are also being
tried, with the object of reducing the number of man hours of
work reouired to get aspen timber from the stump to the plant.
Woods operation of chipping machines, now being studied, would
help to accomplish this while leading to closer utilization.

Host aSpen is cut into a variety of rough products. In the
past a great deal of the timber has been imprOperly or wastefully

cut and often not seasoned. Eurthermore, a large preportion of

aspen lumber is manufactured by small, portable sawmills, and
much of it is poorly sawn and ungraded, producing low quality
lumber at high cost. Zasada and Kleunder (l9h9) have advocated
wider use of the "center split horizontal band re-sawmill" for
the advantages of accurate sawing, large volume production, high
recovery (large overrun), and low cost of operation.

Lack of information as to location and quantity of supplies
of aspen for specific products, and ignorance of the preperties
of the wood, have shared reaponsibility with high costs of pro-
duction and poor utilization practices for creating buyer pre-
judice against aspen. Garland (19h?) pointed out that forest
survey figures are not detailed enough to be useful as criteria
for utilization recommendations and asserted that a series of
type maps showing species composition, age of stand, condition
of stand, and site classification by areas as small as forty
acres is needed. Owners and managers of aspen stands can help
to solve their own marketing problems by advertising the timber
they have to sell. In order to do this successfully, the forest
owner must have made a reasonably accurate survey of his tim-
ber holdings. Furthermore, the owner should be familiar with
the Specifications for all of the products for which a possible
market is available. Fe must then decide what kind of Operation
will most completely utilize the timber he has for disposal, with

greatest financial return. finally, prospective timber buyers

have to be contacted and informed of the amount and kind of timber
for sale. Zasada (l9h9) recommended that they be supplied the
following information: (1) The amount of timber in board feet or
cords, and the exact area involved. (2) The kind of timber, its
quality and size. (3) The location of the timber, distance from
town, railroad siding, and wood-using plant. (h) leans of access
to the timber - highways, woods roads, and trails which pass
through or near the timber tract.

Aspen's poor substitution for many products of the original,
dominant timber species, in/regions where it is new widesyread,
created a general prejudice against the wood which has only gra-
dually dispelled with more complete knowledre of its true charac-
teristics. like any other Species, the wood of aspen has certain
definite use limitations. 0n the other hand, it has distinctive
properties which make it particularly well-suited to some uses
(Zasada, 19h7). In spite of the many retarding factors, the mar-
ket for aspen has expanded considerably during recent years, par—
ticularly in the Lake ttates, because of its relative availability
and some degree of conformance with the reouirements for a growing
list of products.

Aspen wood is light colored, light weight, uniform in texture,
straight grained, and free from staining or odorous materials.

It is fairly easy to work and finish, has a low tendency to split

in nailing, forms strong joints when glued, holds paint reasonably

-75-

'well, and can be seasoned satisfactorily by air-drying and kiln-
drying. These properties are advantageous for use of the wood as
boxes and crating, pulpwood, excelsior, core stock, veneer for
matches and food containers, toys and novelties, and limited small
construction use where decay resistance and great strength are not
necessary. The first three of these products now represent a large
prOportion of the total aspen drain, and the pulpwooi market holds
particular promise for increased demand in the future.

Aspen's low strength and decay resistance, poor nail holding
power, numerous knots, lack of attractive grain, and low density,
combined with the fact that only a limited amount of wide, clear
lumber can be obtained from the small logs, make it less desirable
than many other species for products such as construction lumber,
commercial veneer, railroad ties, mine prOps, fuelwood, fence
posts, high-grade furniture, and chemical wood. fievertheless,
aspen satisfies the reouirements for several of these products
well enough to be used in considerable quantities because of its
greater availability. Lesser amounts of aspen are used for a great
variety of other thinzs, and a complete list of all products for
which aspen is used, to some extent, would probably total in the
hundreds.

ASpen's competitive rating in the lumber market can probably
be raised, but it will require better handling from growth on

the stump to final manufacture. Research must continue to try

to find new uses for small material which will lower the utiliza-
tion limit, forest managers should aim for greater yields of larger—
sized, higher quality logs, improved logging systems are needed

to enable lumbermen to more fully utilize the timber in stands

and leave the land in better condition for future crowth, and pro-

cessing and marketing standards must be raised to command higher

prices.

-77-

Aspen Silviculture

The application of correct silvicultural technioues to aspen
stands is essential for high productivity. Leglectful cutting
practices are conducive neither to thrifty aspen growth nor to
replacement of the type with a healthy stand of other desirable
species. The result of careless cutting is almost invariably a
stand of defective, slow—growing aSpen mixed with other inferior
species and invaded by brush.

Assuming favorable marketing conditions and other economic
factors such as tax rates, the question of profit in the manage-
ment of aspen as a permanent, pure crop depends upon site ouality.
Accordingly, its determination is the first preliminarv to organ-
ized management of aspen lands. Stoeckeler (l9h3) has prepared a
table indicating the recommended choice of treatment for aspen
lands based on the two simple criteria of soil texture and fire
history. negardless of the wner's decision, however, successful
management depends upon planned cuts according to clearly defined
reouirements.

ASpen silviculture need reouire only a minimum of technical
skill to apply and can be varied in intensity in order to adjust
management costs with potential yields from merely a progerly
applied reproduction cut at maturity to the inclusion of frequent,

light thinninas begun early in the stand's life. at present

intensive management is possible only on the best sites, but
great improvements can be made in the condition of most aspen

stands with extensive management methods.

Reproduction Cuttings. It has already been made manifest

 

that aspen's silvical characteristics adapt it to a clearcutting
system, and that because of the Species' avidity for lifiht this
literally means ”clear" cutting. Also eXplained, in the section
on reproduction, was the effect which season-of—cutting has on
aspen's Sprouting ability, and the stimulating effect of disking
the soil following removal of the mature stand. This knowledge
can insure immediate and complete reveneration of aspen stands
if strictly applied.

Conversely, it helps to illustrate the most effective methods
of eliminating aspen to make way for other species. lf economic
conditions or poor stand quality make conversion desirable there
are several effective methods of holding back or destroying aspen
.prouts. ~asically, all involve cutting, girdling, or poisoning.
Girdling has the advantages of economy if the stand is too poor
for commercial cutting, reduced sprouting, and gradual release
of advance growth, but is not adapted to sapling—size stands.
Eoisoning is effective in youns stands (say, l9h7; Egler, 19h9;
and uible, 19h?) and preferable to cutting from the standpoint
of reduced Sproutina, tut may be a hazard to wildlife and manage-

ment.

-79-

when the stand is to be held until maturity an excessiveLy
heavy thinning about ten years before the final removal of the
overstory'will stisulate the production of root suckers which
will be suppressed by the remainin: trees and inhibit develop-
ment of later sprout growth. uirilinf a year before the final
cut discourages Sprout production and cuttins back sprouts a
year after their inception on a clearcut area weakens t“em and
aids outstripping by other species, but several such liberation
cuts are usually necessary (Rudolf, 1950).

Slash disposal can be dispensed with in aspen stands. blash
does not interfere sijnificantly with sprout production or growth,
ani its lowflammability and rapid decomposition classify it as a
minor fire hazard (Boyce, 19h8; uestveld, l9h9). Decomposition
is complete within four or five years.

Limiting the length of rotation is the most important sil-
vicultural tool that the forest owner has for controlling the
amount of defect in a stand. Studies in the Lake Otates have
demonstrated that rotations should not exceed 55 years on good
sites, hS vears on medium sites, and the minimum period necessary
to produce a commercial crOp on poor sites (Lehnsraff, 19h7a).
Some owners may wish to grow larger, more valuable trees by
sacrificing volume, but Lehngraff estimated that the larfer

products must bring a stumpage price approximately three times

higher than usual in order to compensate for the loss in volume
and time. Ihe larger class of products should therefore he grown
only on the very best sites which, with intensive zanagement,
will produce them in a nonnal rotation or slightly lonfer without
involving serious risk.

It is obvious that heavy volume losses can be avoiled only
by cuttinf aspen stands promptly at maturity. i”he first step in

management must therefore be to classify the as an lands according

*r‘i

to site and age classes than an orderly cutting plan may be
adOpted. Harvesting completely and at the prOper time will
usually be fullv sufficient to restore and maintain the produc-

tivity of aSpen lands at a reasonably high level.

Intermediate Cuttin*s. Eor even higher yields of larger,

 

sounder, and more valuable materials thinnin 3 must he resorted

to. is earlv as 1911 neigle and Erothinshem observed the desira-
bilitv of thinninqs, but only within the last twen y-five veers

has serious experimentation been carried on to measure their effects
and discover how best to apply them. The results of studies con-
ducted on the like Lay gxperdfiental.?orest in .innesota have gen-
erally indicated that ”aspen responds excegtionallv well to thin-
ning, especially during early life.” (aehnrraff, l§h7e). evidence

is not complete enough to predict how much thinninrs can increase

,_J
U)
(1‘
1)
:5
:1

the quality and yields of aspez is but presently promises at

least reduced defect and larfier pOS“ib1e Sizes, which alone appear

to justify non-commercial thinnin:s on gooi sites.

Ln unfavorable report on the effects of thinning was made
after trials on the fetawawa Eorcst- rneriasn Ltation in Canada
(”icker°tafl, lShC). A basic difference existed between the
type of thinnin 5 made in this stud3, however, and those which
have been applied on Lake States sample plots. Com ercial
thinnin s were agplied to four young aspen stands of varying see,
site, and density and remea sured ten years later. In order to

make them pay for Transclves and on the greiise that only one

thinning would be economically feasible durinj the rotrtion, th
thinninfs were very he’vy, removing 70—30p of the original stand

in each case. This necessarily removed the larger, more vi;orous
trees, leaving a drastically reduced growing stock of smaller,trees
from the lower crown classes. The sijnific ant feature of the
remeasurement data is that, although the per acre yield ani in—
crement and yield of the thinned :J ots was about the same as for
the unthinned plots ~nd sunsca 1d l'nave ~ni other injuries were
high on the former, the volume increment ‘er tree-was much higher
on the tli nred ts.

Success with thinrin s on the like _ay experimental [orest
has demonstrated that such cuttings shouli be made from Eelcw, with
no at taxi; to make early Operations pay for +rensclves. Irees re-
moved were selected with a tree classification hvsed on visor,

soundness, fort, and utility to serve as a ymuile (“evorkiantz,

E. a. et al, 1?~ “3). free vi"or, as expressed by such exte vial

—f32-

characteristics as (l) gosition in the stand and relation to
surrounding trees and (2) crown density, is the most important
basis for the classification. Irees of low vifior are the wost
defective and slowest Trowinfi, thus arguinf that thinnins from
above defeats its own :ur_ose which is to concentr"te Wronth on

the most promisin: individuals in the stfnd. Ihe trees removed

P.

n thinninfis should he those which are losing out in the struqyle
for dominance, defective trees, and trees which have wounds or
other avenues of disease entrv which make them poor risks. In
addition, other low—value or poor duality hardwoods which inter—
fere with the aromth of the best aSpen should he removed on food
sites where the latter is often superior to its associates. Al-

though gromotinj more rapid fronth, thinnin s of this sort also

serve partially as improvement and salvage cuttinfs in older stands.

(4'

In 1936 a series of hinninj plots was established in a 13-
year old stand of good—site asten and remefsured in 19LS at the
age of 23 (tehnaraff, lyhtd). Accordini to the results voung
aspen responds to thinning almost in direct relation to increased
Spacin s u? to 8 feet ov 9 feet. Fracin s of 7 hv 7 feet and

3 feet by 9 feet oxfer the best possibilities for managenent.

If the plots thinned to these Spacin s in the exteriment had teen
clearcut for pulpwood in 19h5 added growth alreaiv would have
paid for the thinnine costs.

hecent experimental, non-commercial thinninis in ll-and 20—

year-old stands indicated that thinnins costs are much lower

I

at 10 than at 20 veers {Lake States :orest uxperiment itation,
1952a). notwithstandinc the fact that in the older stand only
dominant and codoninant trees that were interferinv with selected
crOp trees were removed while all out COJ to 900 o: the best trees
per acre were left in the younjer stand, the earlier thinninf‘was
more economical because of creator time reeuired, even after fro-
jection of the yrevailinn wage rates at S For cent.

:en stands reach tulpwood size it annears that partial

F4
C?
(D
’1
P.)
U)

cuttinas of moderate severity can be male to advantage from above,

or at least without serious detrimental after—afiects (sehngraff,
9h7a). uiameter limit cuttings of 3, 9, and 10 inches were

tried in a L3-vear-old stand on a EOOj site on the rike pay

Experimental zorest in 1935. neneasurenentS‘siX veers after

cuttina revealed that the lO—inch diameter-limit cutting had fro-

duced considerably more total volume than any of the other cuttina

plots and slifhtlv more than a check slot. 'A 9-inch lifteter-

J.
U

3.4;

u ied on an optimum siie for asnen in Prisons.

. .4. ' —t ... --ofir‘
limit cutter;~ an;

(7)

A residual stand of SSL cubic feet/acre in trees four to eight
inches in diameter was left, and remeasurements five years later
found that growth exceeded by one and one-half to two times that
of comparable stands of ponderosa pine.

however, the objections citet above to this form of cutting

still apply if the residual stand is too small or deiective.

— -‘lJ -

‘ff cautioned that cuttin s from above should not exceed

I“

to per cent of the nerchnntshle Sath" volume eni ehout 15 per cent
of the merchantehle trees. economic coniitions yermittinj such
intermediate cuttings shouli also he made fro: below, utilizin:
small merchantable trees and some larger trees of poor form,

quality, or risk.

THE ASPEN EfiOcLbn AhD CQUJSLS OE AClIUh

The aspen problem is a part of the much larger land use
problem left in the wake of the wave of destructive exploitation
which, in less than a century and a half, enveloped most of the
great timberland regions of the United States. hith the end in
sight for the last of the high-grade, virgin timber, this country
is left with vast areas of unproductive or partially productive
lands still languishing from the effects of the economic blight
which followed exhaustion of the original timber supplies. for
the most part, these lands are fitted only for the production
of timber crOps and, in large measure, the peOple must look to a
regrowth of the lumbering industrv for a brichter economic future.

Revival of the forest lands has been particularly slow in
the Northeast and the Lake States despite a high concentration of
wood-using industries, and it is in these regions that the aSpen
type reached its greatest eXpansion. us an interim protective in—
fluence which lessened the deterioratibn of denuded lands, aspen
performed a valuable service, but, with contemplation of accelerated
forestry programs for restoring the forest lands to full produc-
tivity, aSpen areas present a particularly difficult problem. So
great is the area of the aSpen type that in syite of an expanding
market for the Species the demand will apparently never equal the

supply; definitely not in the foreseeable future. neanwhile, aspen

has not outgrown its unofficial classification as an inferior
Species and discrimination against it continues. fhough able to
out-produce other Species in total cubic volume, it will never be
able to compete in satisfying the Nation's great future reouire—
ments for high-grade saw timber, needed both for peace and as a
reserve supply in case of war. for are the revenues derived from
aspen, on medium and low ouality sites. certainly.comparab1e with
the potential returns from other species.

In their present state, a large majority of the aspen-bearing
lands afford little or no income for their owners, and, in fact,
represent a real economic loss to the pOpulation at large by
their idleness. The huge areas of land preempted by the aspen
type could be growing much more valuable ti ber creps and halting
the decline of the lumbering industry in these regions, but in-
stead are generally only a financial burden to local and state
governments which must supply them with governmental services re-
gardless of their productivity.

Increased production from aspen lands is clearly vital to
the forest economy of the Lake States and the hortheast, and is
highly desirable in other regions where aspen has even less value.
A number of serious difficulties have, however, hindered progress
toward that end, most of wnich have arisen from the very fact that
these lands are of low value. ihe great ouantities of aspen in

comparison with the limited market and low value, the {00? quality

and low stocking of the large majority of stands, costly and in-
efficient logging methods, and low yields of merchantable size
material have discouraged ownership of aspen lands, with the re-
sult that a majority of them has now become public owned through
ta forfeiture or purchase. Ihese same factors,plus lack of ex-
perience and technical information,have been prohibitive to
planned management for sustained yield.

Those aspen lands which are publicly owned are largely of
the lower site and aje classes, and these are divided amongst
several levels of government. lrivate companies generally own
better aspen lands, but lack sufficient consolidated acreage and
a proper distribution of aye classes for effective management, and
most small woodlot owners are indifferent about management of
their stands. Thus, "management" to date has consisted almost
exclusively of necessary fire protection, with the exception of
experimental work carried on by the federal government. The
natural consequence has been continued improper cutting, resulting
in even greater areas of defective and under-stocked stands.

It is obvious then that the magnitude and complexity of the
aspen problem will necessitate maximum cooperation and coordination
of effort between private forestry and the public agencies con-
cerned with land use for an effective solution. The recuired long

range nature of whatever formal measures were adepted and the large

government ownership of aspen lands further indicate that the
public would have to supply the initial impetus and carry the
major part of the burden of execution for any program decided
upon. For obvious reasons, the initiators and directors of such
plans would have to be the states, specifically the state forestry
agencies. however, the assistance of all government departments
supervising land resources would be indiSpensable.

Three alternative courses of action for develOpi g aspen lands
are apparent: (l) planned management for aspen, (2) conversion to
more valuahle Species in the near future, or (3) temporary manage-
ment for aspen with conversion to other species after one or more
rotations. The decision in the case of a particular stand re-
quires consideration of a number of factors, including site quality,
age, density of stocking, amount of defect, character anr density
of the understory, ownership status and condition of surrounding
forest lands, and marketing possibilities.

Generally Speaking, the primary consideration must be site
quality. In view of the tremendous area of aspen, and its site
sensitivity, aspen management not only logically should but must
be concentrated largely on the most productive sites, or those having
a site index of sixty—five or higher. hedium and low cuality sites
are usually characterized by light soils originally occupied by
conifers and best adapted for conifer growth. tn the other hand,

medium sites already being successfully nana ed for aSpen would

of course retain their status, at least temporariLy, and some

of the better medium sites should be managed for aspen where
marketing conditions are particularly favorable for small-sized
material or in cases of need to expedite management over a wider
area.

Planting on the best aspen sites, meaning usually those sites
originally occupied by high-ouality northern hardwoods, should be
very limited. establishment of conifers on these sites is un—
desirable if favored hardwood species can be grown, and the risk
involved in planting hardwoods is too great to justify such a
venture while much greater areas of aspen land await planting of
conifers. aiven time, most aspen stands on these sites will
revert naturalLv to more tolerant hardwoods and the indicated
method of handling, if conversion is the objective, is extensive
management with cuttings favoring gradual ascendancy of these
species.

As a result of the recent, great and continuin: strides made
in the fields of utilization and silvicultural research, profitable
sustained-yield management now seems feasible for millions of
acres of aspen land. Zehnaraff (l9h9) has defined the objective of
aspen management as ”ouality production," pointing out that be-
cause of the great waste in aspen every year, due to poor quality,
this would be tantamount to greater r‘uantity production as well.

Improved ouality is the best remedy for many of the utilization

-90-

ills still plaguing aspen and if these could be minimized the
obstacles to aspen management would be no vreatar than for other
Species. In fact, aspen's natural attributes adapt it to an
inexpensive and simplified form of manafiement. It grows in re-
markably regular and even-ajed stands under normal conditions,
allows a short rotation, hrs little tendency to stagnate seriously
yet responds well to thinning with added frowth on good sites,

and is surely and promptly reproduced if certain precautions are
observed.

Intensive management practices are not now practicable on a
large scale, but must be limited to small holdinas and the better
organized lands of a few private companies. Ihe immediate goal
must be to organize the lands of individual owners for more in-
tensive future practices by segregatin: stands into separate
site and age classes, and to adOpt a cutting policy which will
improve stocking and establish an eoual distribution of ace
classes while utilizing the existing mature timber as completely
as possible. In this connection it is essential that fire pro-
tection be maintained, and even increased in some areas, and
that logging practices be improved to prevent the spread of aSpen
to new areas and the further deterioration of those sites on which
it is alre<dy present.

The states and federal government and the larger industries
are pro:ressing fradually toward continuous long-range manafement

on their forest holdings, but, notwithstanding technical assistance

available throufh the extenSion service and s;ate forestry agencies,
small owners have lagged far :ehind in snwlyin; organiaed management
to their stands. fhe small owner stands in need 0
and more detailed program of assistance, yarticularly from the
standpoint of marketing.

flew Jersey has made commendable {regress in this direction
through a cooperative plan involving several public agencies and
private enterprise. The step most instrumental in its success
has been the employment of private timber agents to arrange and
supervise marketing of timber crepe, which has strengthened the
owner's bargaining position and resu ted in improved harvesting
practices, thus leoving stands in better condition for future
growth .

Eventual conversion to coniferous species seems to he the
best choice for treatment of the majority of medium and low ouality
aspen stanis, and is the course ievored by most trofessional
foresters as well as private owners. conifers are capahle of pro-
viding much freater returns on these sites, and there is a present
compelling need for softwood timher in the Lake States and the
Northeast. Shirley (lSLl) estimated that the total differential
between the values created by products now grown on all aspen and
brush lands in the lake States and the yields which probablv could
have been obtained from these lands, had they restocked with the

original timber tvpes, amounts to about 916,000,000.

Stands in which there is already stocking of other desirable
Species,whether coniferous or hardwood, in the understory should
naturally be manaeed in such a manner as to preserve this advance
growth and insure natural conversion as soon as is reasonably
possible. Cutting of mature aSpen should give nrioritv to release
of valuable snecies from surpression, and unmerchantable stands
should be *irdled wherever practical. lnfortunately the area of
aspen land upon which there is adenuate retroduction of conifers
for well-stocked stands is very limited because of the severe
conditions to which most sites have been subjected. The prooor-
tion of aspen lands bearing an appreciable stocking of conifers
in the lake btates was estimated at between 10 and 2o per cent,
with balsam fir, a low value species itself, comprisin: more than
half of the total (Littredee and qevorkiantz, 1929). Further-
more, field observations demonstrate that conversion of aSpen
lands in this region by natural succession m st be expected to
reouire at least a hundred years under the most favorable con-
ditions (nudolf, 1950), and in the hooky hountains one hundred
fifty to two hundred fifty veers (baker, 1925).

The situation in the Lake States and the northeast is too
urgent for natural transformation to be considered a satisfactory
solution. In summarizing the exoerience and findin:s of Lake
States foresters and weighing the probably costs and returns of

converting aspen lands, chirley (19h1) called for a public

__n‘3

//""

planting program. Calculations indicate that the costs of plant-
ing aspen lands, though hizh, could be met by the returns in the
form of timber rrowth durinf the first rotation. frofits, if any,
would not be sufficient to motivate large-scale private planting
projects but the potential, adled social and economic benefits

to be derived seem to fully justify the expense of a public pro-
gram.

Actually, what is needed is a single program desiened to
resolve the aspen problem in its entirety. In many states, govern-
ment and private enterprise are, and have been for some time,
attacking the problem in as many ways as possible, but their
efforts have only been partially coordinated and on too limited
a scale to make app eciable headway. The administrative, tech-
nical, and economic difficulties involved in formulating and
executing a definitive program for rejuvenation of the aspen
lands are such that no single authority could undertake the
task alone. Loreover, if maximum returns and efficiency were to
be achieved action could not be unilateral, for the interests of
regions and communities as well as individual owners must be
served, particularly since the public would have to underwrite a
large share of the program.

ho iumediate large—scale action could be taken for several
years after a program were decided upon in principle for time

would be required to supplement the backéround of information

and eXperience already ac uired in handlin? aspen lands and to
serve as a trial period for testing and improving procedures.
Realization of the final goal would take a treat many more years,
and foresters should take action now if many of the potential

benefits are not to be lost.

CONCLUS I ONE

1. Aspen is very exacting in its requirements for good growth.
Loweite quality markedly effects. the species' susceptibility to
decay, form, and rate of growth. Knowledge of-site quality is,
therefore, extremely important to intelligent handling of aspen
lands.

2. There. is a \eound demand for good aspen in operable quantities.
Barthel-more, it appears that the demand. can be expected to increase
in the future, and value with it- Preper management can do much to
enhance the value of the epecies'by increasing the supply of high-
quality material. A

5. Only vigorous growthcan hold damage. from aspen's many natural
enemies to a minimum, and consequently management for. aspen on a
pemanent basis should beconcentrated largely on good sites

where the healthiest stands naturally occur and where response to
management is most pronounced.

‘1. Limiting rotation age is the most important measure applic-
able; to individual stands for obtaining maxim. yields of rot-
free material, and. thereforeage, as well as site-quality,
detemination is essential for instituting managementof aspen.

5. Full stocking and optimum growth of succeeding generations of
aspen can be assured only by complete. removal of the overstory
during the final cut, either by cutting alone or some combina-.

tion of cutting, girdling, and poisoning. Adequate regeneration

is also less certain following cutting during the growing season
than during the dormant season.

6. The effects of fire,.even though light, may be disastrous to
plans for management. Firesedirectly damage and kill the, thin-
barked aspens and, increase the liability to disease and insect
attack, by. reducing vigor and providing points of entry, and,
finally, lover site-quality semi-permanently. in efficient fire
protection system should be an integral part of all management
plans.

7. Aspen iavery adaptableto intensive silviculture .on-good sites.
The dminant and most vigorous, individuals in a stand are quick to
take advantage of increased growing space provided by thinnings.

_ Experiments to date have indicated that. thinnings are best applied
early,-frequently, and. lightly, and should be fran below.

8. On medium and pooreitee aspen loses its: advantage of high
volume production for a given period. Conifers are clearly superior
from the standpoints ofboth volume and value returnsand should
supplant aspen as soon as is practicable. The condition of most
aspen lands is such that natural succession to more valuable
species will not occur naturally for. an inordinately long period
of time, and the econanic welfare of many forest industries de-

mands an expanded program of forest planting.

RECOMMENDAT IONS

The experience in cooperative organization and information
being gained from various research projects and the National
forest survey are providing a useful springboard from which many
states- could launch more ambitious programs of forest improve-
ment than was ever before possible, if, and when public support
could be mustered. The exact knowledge of present condition and
potential capabilities of the forest lands now becoming available I
provides the basis for the kind of well-founded, comprehensive
plans'which make large-scale action possible.

. As forest survey work is being completed the states should
take the initiative in directing detailed analysiseof all public '
lands tosdetermine the. best possible method of handling them for
the long-range benefit of the public at minimum cost. The ob-
jective is, of course, to increase- and stabilize the flow of
forest products so that. forest industries, canmunities, and in-
dividuals who depend on them will be assured of a steady and
substantial income. Successful planning of this task will re-
quire the assistance of all groups concerned with the problem.

Plans for the public lands should be designed partly to
cmplement and aeeietthe plans of private. owners for the mutual
benefit of both. This implies the necessity for consultation

between public and private landowners to pranote integration of

future management plans, insofar as possible. State forestry
‘ agencies should serve as‘a depository for and clearing house
for the exchange of information and plans.

Conversion of a large percentage of the publicly owned aspen
lands will doubtlessly be desirable and an accelerated program
of planting should be high on the agenda for public action». .
Planting should been a firm basis of anticipated coverage of
the costs within one rotation. This would eliminate many of the
poor sites, at least temporarily, and relegate them to other uses
than the production of timber crops such as recreational and
wildlife areas. One consideration in locating areas for planting
should be the possibility of hastening natural conversion of
lands on which planting is not presently possible; 1

Better management of aspen lands not slated for imediate
or eventual conversion can be achieved only by continued re.-
search and education combined with gradual improvement of the
physical and semantic conditions created by our fonner careless
treatment of the forest lands. A clear and thorough analysis of
the objectives and the required measures for the Lake States,
which has universal application, was presented in the report of
the forest resources for that region(U.S.D.A., Forest Service,
1950). The measures which are particularly important for stimu-
lating management of the aspen lands are those needed to stabil-
ize ownership and promote sustained yields, including consolie-

dation of holdings for better administration, integration of

-99.

management plans, removal of'legislative obstacles to good manage»
ment, and employment of all available aids.

Two other measures which the author suggests for study are
a larger program of assistance to the small woodland owner and
cooperative management arrangements for the public lands between the
government and private enterprise. A large proportion of the
forest land, much of it capable of prod cing good timber, is in
the hands of small private owners, largely farmers, who are
doing little to increase its productivity although such holdings
are ideally suited to intensive management. Technical assistance
has been supplied, but the owners need additional aid in marketing
their crops to advantage and enfbrcing proper cutting regulations
to leave the lands in good condition.

Many forest industries need to acquire additional areas of
land to balance age and site~class distributions for instituting
sustained-yield management. These companies often could not afford
to buy this land outright and sustain the additional costs which
might be necessary to plant or improve the condition of growing
stock on them, but neither is the public able to apply more than
the barest essentials of management to much of its land. Leasing
arrangements which would defer the costs of purchase until profits
were ferthcoming from the land or by which the public would
retain ownership and share income from the land until under
well organised management would seem to promise benefit for

both parties.

-100-

APPENDIX

-101-

r.3Ls I
Yield of Second-Growth Aspen, Trees Seven Inches and Over,

Scribner uecimal 0 log mule

 

 

 

 

 

Kind of Age Trees per Average Average Basal area Volume
Site Acre 7 height Diameter, per per
inches breast acre acre*
and high
more --_‘fi._‘
iears ho. Feet 1nches Sq. feet board ft.
Good.... 30 35. 69 7.3 10 500
ho 167 70 7.6 52 3,bOO
50 297 72 8.1 103 9,600
60 293 77 9.3 135 17,3 0
70 235 82 ‘ 10.9 150 23,600
80 130 86 12.6 15h 27,hoo
iedium.. b0 68 65 7.5 21 1,000
50 213 66 7.7 69 b.300
60 300 68 3.3 112 10,300
70 268 71 9.5 132 16,b30
33 229 7b , 10.6 1h0 19,700
Poor.... SO 68 55 7.h 20 1,000
60 17b 59 ' 7.6 55 3,200
70 2b0 60 8.0 8h 6.600

*Stump height, 1 foot; tOp diameter inside bark, 6 inches. Bark
is not included in volume.

-102-

TABLE II
Yield of second—drowth Aspen, Trees Six Inches and Over,

International Log Ru1e*

 

 

 

 

 

Kind of Age Trees per Average Average Basal area Volume
Site Acre 6 height diameter, per per
inches breast acre acre**
and high
over
Years ho. Beet inches 50. feet Board ft.
600d. 0 o o 30 170 63 6.0 33 3 ’ S'JJ
to 319 66 6.7 80 9,200
50 h03 70 7.6 12h 16,700
60 320 76 9.0 1L3 23,700
70 235 82 10.9 151 30,100
80 130 86 12.6 155 3h,800
ledium.. 30 30 59 6.1 1H 1,L00
no 215 60 6.3 hS 5,000
50 358 62 6.9 96 10,700
60 378 66 7.9 127 16,500
70 290 70 9.3 138 21,300
80 23h 7h 10.6 1L3 2h,800
Poor.... to 7b S?“ 6.1 13 1,h00
SO 200 Sb 6.h h2 h,500
60 306 55 7.0 81 3,200
70 327 59 7.6 102 11,500

 

* Based on a l/8-inch kerf.
**Stump height, 1 foot; t0p diameter inside bark, 5 inches. Bark
is not included in volume.

-105-

TLELm III
Cordwood Yield for'flell—Stocked Aspen in Trees Four Inches

and Over in Diameter, Ereast high

 

 

 

 

 

 

 

Kind of Age Average total Average basal area Feeled volume—
Site height of diameter per per
dominant breast acre acre*
trees high
Years Feet 1nches Sq. feet Cordsat

Good.... 20 b0 2.9 83 57

30 51 l: .2 102 25

ho 62 S.h 120 h3

So 70 7.0 133 SS

60 76 9.0 1hh 43

70 02 10.9 151 67

80 86 12.6 155 69
medium.. 30““ LL 3.5 9D 12

to S3 h.S 110 30

50 60 5.9 122 Lb

60 66 7.6 133 51

70 70 9.3 139 SS

80 7h 10.6 1h3 57
Poor.... hO , hh 3.5 53 11

50 50 h.6 93 26

60 55 5.8 105 33

70 59 7.1 109 37

 

* Stump heifiht, 1 foot; to; diameter inside bark, 3 inches.
**%Standard cord, h by h by 8 feet. Close piling. Volumes in

cords were obtained by applying the factors used for conversion
of merchantable volumes in cubic feet to cords to corresponding
average diameters at breast height. As a check, the same results
were obtained from curved distributions of stems of different
sizes per acre for a given age. These latter curves were also
used for obtaining volumes in cords for stands with average
diameter less than h inches.

ASpen normal Vield lable Adjusted to forest Survey

standard of Ltilization

 

 

 

 

 

 

 

 

Age ho. :asal Ave. Gross 'v’01.-L Let VolumeC rulpwood
Years Trees Area Uifi bi. rt. Total 66. Ft. 36131' Cords
rer 1 So. bcrib. Cords Scrib. Cords
AchEt.
Fest hardwood land
20 1,703 90 3.1 —————— 3.5 ------ 2.7 1.6
30 1,05u 107 h.3 50 17.3 28 1F.8 6.9
to 757 126 5.5 970 36.3 hlh 20.6 11.3
50 h95 137 7.1 3,730 52.1 1,720 31.7 16.2
60 330 1h5 9.0 12,910 61.1 5,690 h3.h 12.1
70 235 152 10.9 21,730 66.5 10,150 50.3 5.2
80 130 156__12.6 25,750_ 65.5 12,230 52.0 2.h
§Eruce balsam Land
20 1,889 50 3.0 ------ 2.8 ------ 2.7 0.2
30 1,211 103 3.9 --——- 12.5 ------ 9.2 1.5
no 866 123 5.1 325 30.2 106 20.0 h.9
50 570 130 6.6 2,795 h6.9 937 30.9 11.3
60 376 1L2 8.3 9,020 55.7 3,130 37.7 15.1
70 265 lh6 10.1 16,6112 59.11 6,271 39.9 3.7
8 206 152 11.6 21,275 61.5 7,520 b0.5 5.1
irine Land

20 2,062 90 2.8 ------ 271 ------ 2.3 0.3
30 1,363 101 3.7 ------ 9.9 ------ 7.8 1.6
to 972 11h h.6 165 22.2 an 16.2 h.h
50 6h3 125 6.0 1,295 38.2 565 26.6 9.2
60 L22 135 7.7 5,515 b9.7 1,973 21.2 11.5

 

1. Gross Jolume includes all livinfi trees
(a) loard Feet tcribner - frees 9.0” and over to 6” top
(b) Total Cords - Trees 5.0" and over to 3" top
2. let Volume includes only the usable portions of merchantrble trees.
(a) ioard Feet Scribner to variable top-nfnimum 6"
(b) Coris - to h” top inside bark
(c) tulpwood - includes portions of trees suitable for pulpwood
to 5” top which have not been utilized for sawlog.
3. Trees 1” and over

-105.

TAELE V

Yield Table of Aspen by Age and Site Classes

 

Site Classes

 

 

 

Standard Cords Board Foot Scribner
Age Classes Good med. Poor Good Led. Poor
20 8 - _ - - _
25 19 7 - _ - _
30 . 29 16 5 1300 300 -
35 36 2h 13 h000 1000 -
to L2 30 17 7000 3000 1000
hS . L6 32 18 6500 5000 2000
50 h? 33 16 9000 6000 3000
55 M6 30 13 9100 6000 2900
60 L3 26 10 9000 3300 2500
65 37 20 6 3u00 5200 1300
70 29 1h 0 7600 0500 1LOO
75 21 9 - 6000 3200 700
60 12 h - L200 1500 -

 

These volumes are based on the following heights of dominant trees
at 50 years:

Good Site - 72 ft.

Led. Site - 66 ft.

loor Site - 55 ft.

Cordwood volume is the :ross volume in standard cords of peeled wood
in h" D.B.H. and larger to a minimum ton diameter of 3" inside bark.

Board foot volumes are gross volumes by the scribner rule of trees
7ND.B.E. and larger, the minimum tOp diameter bein: 6" inside bark.

l.

10.

11.

12.

13.

-106...

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hittredge, J. Jr. Interrelations of habitat, growth rate,
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Llirple, E. h. 1re1iminary merchantable height volume
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Korstian, C. r. mole of aspen in reforestation. Soc. Em.
For. Lroc. 11: 133-10b, Jan., 1916.

Krefting, Laurits n., and forest 5. Lee. Proeress report:
Loose browse investigations on Isle novale sational
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hrefting, laurits J., and Erank d
Deer browse survev of the macei
p

partin. Special report:
1 hail
necedah, his. 18 pp. tvpescri.

ah national dlife nefuge,
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Larson, George C. sore on seedlinss of western aspen. Jour.
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Lake étates forest experiment otation. fire hinders con-
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reb., 1931.

crowing big er and

 

better asnen. Lech. note #52 rev 23 1932.
e , - ,

Aspen normal stand

 

tables 0 l'eCh. i-Ote {I 71’ LKOVQ , 19330

klanting under aspen

 

can be made successful. Lech. note 930, hay, 193E.

 

A_» Thinning in aspen.
Lake states ror. sxpt. Sta. Forest hesearch Digest,
p. b (processed), harch, 1‘w5

I.)

 

pine from aspen. Jour. for. 33: l7h-175, 1999.

119.

120.

121.

127.

123.

129.

130.

.1

131.

-115—

lake States Forest experiment Station. Urowth rate of aSpen

I.

indicates potential forest c var. Tech. Lote. 592, aug.,
193 .

Treatment of aspen

 

stands. gfipp., illus. (yrocessed;, hov., 1935.

 

There's profit in

n. lfike States ror. prt. Eta. Forest Aesearch Di-
.“ ,4
est, 1:?" 9—10 (prOCBF-Fet'l), .JBCo, 193.30

{1)

C‘ \
x.) 1’

"1
(D

(M

oirdled aspen good

 

for fuelwooi. Lake atttes Jor. AApt. Uta. borest hes arch
Di:est,3 orinq 1933, yr. 6-7 (processed), 193i.

Uvernniof hhfier

 

from aSpen bolts. Zech. note fi21b, ipril, lflhh.

Taper table for

 

aSpen (repulus tremuloid s) - hell stocked stands. Lech.
1‘.Ote [l'r2b6-‘, Jan. , 191-LL70

iields of aspen in

 

.‘I ’V ‘ y- r), '1)
:Jk)’ £1111], 17': .10

unmanaged stands. Lech. note n

Leasing costs of

 

 

aspen. Iech. note fi3UL, Lct., lGLB.

heleasing white

 

 

pine from oak and aspeL. Iech. note fi3h6, Jan., 1951.

Jiskinz to increase

 

 

stocking in aspen stands. Lech. ,ote #357, July, 1951.

. Diskinq to regenerate

 

 

pulpwood Species. Tech. note #372, April, 1952.

lehor costs for

 

thinning young aspen. Lech. note #37L, April, 1952.

Aspen and birch

 

 

follow pine cutting in northeastern ginn. Tech. note
.A J ‘ r -,r’
1753, Way d3, 1932.

Long, n. h. in uniescribed canker of p0p1vrs and willows

caused hv OytOSpora chrvSOSperma. Jour. of ag. fies.
Vol. Xlll(é): 33l-3b6, 1915.

139.

lhOo

1h2.

1h3.

1h1

1L5.

~116-

Lorenz , a. J., and C. n. Jhristensen. % survey of forest
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Luz er, Otto. Insects affecting poplars and willows. Lniv.
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Lunt, h. u., and 1. 0. baltz. Easal area in relation to
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LcCallum, 5. u. Lajicladium tremulae. A new disease of the
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Leinecke, a. f. fathology of cuakinc aspen in Utah in
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Reinecke, i. P. Cuaking aspen: a study in applied forest
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hoes, s. h. Ihe vegetation of Alberta. IV. »Ihe poplar
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Jour. of LCOlOgV, 20(2): 3dO-L15, illus., 1932.

Longevity of seed and establishment of seed-

 

linas in species of Populus. Bot. Uaz. 99: 529-Sh2,
1933.

nott, D. u. The large aspen tortrix in new orunswick. Gan.
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June, 1951.

Packard, F. a. hililife and aspen in hooky mt. national
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Sex and visor in IOpulus. icience 103:

rauley, S. S.
cept. 17, 19D8.

302‘3339

Forest tree yenetics research: Iopulus.

-.- ....—

ucon. Lot. 3: 299-330, July, 19h9.

'lbéo

1L8.

lh9.

151.

152.

153.

156.

157.

-117-

rearson, u. A. lhe role of aspen in the reforestation of
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Peterson, L. U. T. Some aspects of the pOplar borer,
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Phelps, V. E. heart rot of aspen. Canada uept. of
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Pomerleau, a. Stuiies on the inkSpot disease of poplar.
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Fovah, A. H. u. fittack of poplar canker following fire
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hypoxylon p0p1ar canker. Phyto. 1h:

 

ltd-1115, 19211.

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hegnier, h. hole of insects in the prOpagation of the
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fieim, Paul. fieceneration biol. of aspen on the basis of
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Riley, C. 8., and J. E. Bier. Extent of decay in p0plar
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Riley, C. 8., and A. J. holko. The pathology of permanent
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159.

161.

162.

163.

16h.

165.

'166.

167.

169.

170.

171.

-118-

Roe, b. 1. Forest soils, the basis of forest manaéement.
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Effect of grazinfi upon aspen reproduction.
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Sargent, C. S. Lanual of the trees of north America.
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Schantz-hansen, T. harvesting younfi aspen on the Cloouet
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A preliminary study of several leasing
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Logginv methods and peeling of aspen.

 

Lake Dtates hspen deport Lo. 3., 1h pp. Lake States For.
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Schmitz, L., and L. H. h. Jackson. heartrot of aspen with
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Scholz, Harold B. will pine or aSpen dominate minnesota
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Schreiner, L. J. Freliminary survev of hypoxvlon p0p1ar
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mole of disease in the arowine of p0plar.

 

Jour. ror. 29: 79-32, Jan., 1931.

Two species of Valsa causing disease in

 

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172.

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17h.

175.

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I‘Sh o

185.

-119-

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__‘ Does light burnine stimulate aspen suckers?
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Hill pine or aspen dominate Linnesota
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nestoring conifers to aspen lands in the
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Thinning and regeneration eXperiments in a
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Stoeckeler, J. E. Mhen is plantation release most effec-
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5
soil properties and fire. Joux. ior. L6: 72
19,4 C), o

 

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1,19Ll

 

C

LC

21')
a
./

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202.

203.

20h o

205.

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Aspen management problems of the Lake
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Thinning of dense young aSpen is a good
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Aspen suckers can produce well-stocked
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I725? 3 Jilly, 1(,")‘é o

 

Thinning young aspen can pay. Lake étates
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Possibiliti s of managins aspen. Lake

 

O
, , V7 p - ‘3
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n suckers to over-
ta. Lech. Lote

 

iesponse of younv aSpe-
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s
L
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Zillgitt, h. . Disking to increase stocking in aspen
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