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20AM

This is to certify that the
thesis entitled

THE INFLUENCE OF INITIAL TREE SIZE ON GROWTH,
CANOPY DEVELOPMENT, AND PHYSIOLOGY IN THE
URBAN ENVIRONMENT

presented by

MATTHEW PAUL ROSS

has been accepted towards fulfillment
of the requirements for the

MS. degree in HORTICULTURE

 

 

 

I K/Mbr Professo‘iﬁgnature
12/8/20 8

Date

 

MSU is an Affirmative Action/Equal Opportunity Employer

PLACE IN RETURN BOX to remove this checkout from your record.
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THE INFLUENCE OF INITIAL TREE SIZE ON GROWTH,
CANOPY DEVELOPMENT, AND PHYSIOLOGY IN THE
URBAN ENVIRONMENT
By

Matthew Paul Ross

A THESIS
Submitted to
Michigan State University
in partial fulﬁllment of the requirements
for the degree of

MASTERS OF SCIENCE
Horticulture

2008

ABSTRACT

THE INFLUENCE OF TREE STOCK SIZE ON GROWTH, CANOPY
DEVELOPMENT, AND TREE PHYSIOLOGY IN THE URBAN ENVIORNMENT

By:

Matthew Paul Ross
Proper selection of tree size is essential to maximize the efficiency of canopy restoration
efforts. Municipal and landscape ordinances often specify the use of large caliper trees,
7.6 cm (2.5 in) or larger, to provide a more substantial impact. However, the costs
associated with transplanting larger caliper trees can have a negative impact on planting
budgets resulting in fewer trees planted on a site. In this project three hundred trees of
ﬁve different stock sizes 4.4 cm (1.75 in), 5.1 cm (2 in), 6.4 cm (2.5 in), and 7.6 cm (3 in)
balled-and-burlapped, and 4.4 cm (1.75 in) bare-root stock were planted in four Michigan
communities. Our objectives were to: 1) Quantify the inﬂuence of stock size on growth,
canopy development, and physiological function during establishment 2) Characterize the
relationship between soil and environmental factors on growth and tree physiology in the
urban environment 3) Provide recommendations to municipal arborist to increase the
efficiency of canopy restoration programs through proper size selection. Our study
quantiﬁed the differences in growth, canopy development, and physiology of Autumn
Blaze maple (A cer x ﬁeemanii ‘Autumn Blaze’), swamp white oak (Quercus bicolor),
and Bloodgood London plane tree (Platanus x acerfolia ‘Bloodgood’). During the ﬁrst
two years of establishment, signiﬁcant differences in the rate of canopy development,
trunk growth, and shoot elongation suggest that smaller trees establish at a faster rate than
large trees in the urban environment. However, the relationship between stock size and

gas exchange was not signiﬁcant.

-Dedicated to my late grandfather, Harold M. White, who taught
me the valor in good, honest hard-work

iii

ACKNOWLEDGEMENTS

First and foremost I would like to thank my loving family and friends; without
their love, support, sacriﬁces, and understanding I would never have completed master’s
program. I would like to give special mention to a former Michigan State University
graduate student, ofﬁcemate, and mentor Roberto Lopez who guided my graduate student
career. Aaron Warsaw, my other ofﬁcemate, helped and supported my eﬂ‘orts whenever
it was most needed. I would like to acknowledge my major professor Dr. Robert
Schutzki for his dedication to my program and for allowing me to deepen my
understanding of horticulture and love of extension. My committee members Brad Rowe,
Bert Cregg, and Frank Telewski were vital to the completion of this project, especially
Bert Cregg whose statistical genius brought my program to the next level. Without the
help of the municipal forestry departments’ assistance in Ann Arbor, Lansing, Rochester
Hills, and the Greening of Detroit’s Green Core staff members the project would not have
been a success. Their commitment to the maintenance and interest in the project was
helpful and I hope there continues to be a good working relationship with their operations
and employees in the next eight years of the research. City foresters Kay Sicheneder
(Ann Arbor), Joseph Sulak (Greening of Detroit), Irene Cahill (Lansing), and Gerald Lee
(Rochester Hills) deserve acknowledgment for assisting in the coordination of the
installation and data collection over the past two years.

In addition I would like to thank the 163 volunteers, forestry, parks and
recreation, and student help that helped plant and collect data on the 300 trees utilized in

my research. In particular Adam Newton, Matthew McConegie, Kenny Alt, Rhianna

iv

Winfrey, Erik Pederson, Lacey Conley, Kurt Dempsey, Jaime Anderson, Jeremy Clark,
Dustin Corr, Ian Smith, Katherine McKinley, Alicia Lawson, Aaron Warsaw, and Carl
Suedhoff for their assistance in planting, pruning, watering, and data collectiOn. I would
also like to extend my thanks to Alvin Smucker and Darryl Warncke for the use of their
soil testing equipment, laboratory space, and instruction from their graduate students and
technicians; Lisa McGiveron, Lauren Beaty, and Cory. I would like to thank Dan
McGuire and his staff; for making the facilities at Fuller Park Pool open for data
collection and storage. The generosity of the Michigan Nursery and Landscape
Association was un-paralleled in regards to their assistance in developing my extension
experience. The funding for this project was provided by the Michigan Department of
Natural Resources, Project GREEEN, the Michigan Nursery and Landscape Association,
the United States Forest Service, the forestry departments of Ann Arbor, Lansing, and
Rochester Hills, and the Greening of Detroit who provided the backing of my program

and for their commitment to Urban Forestry.

TABLE OF CONTENTS

 

 

 

LIST OF TABLES viii
LIST OF FIGURES ................................................................................ x
TREES, PEOPLE, RESTORATION, AND THE URBAN FOREST.- _ 1
The Urban Forest ................................................................................................................ 2
Tree Growth and Development in the Urban Environment ................................................ 7
Status of Michigan’s Urban Forest ................................................................................... 12
Urban Forest Restoration .................................................................................................. 13
Summary ........................................................................................................................... 21
Literature Cited ................................................................................................................. 27
THE INFLUENCE OF I‘NTIAL STOCK SIZE ON TREE GROWTH AND
CANOPY DEVELOPMENT IN THE URBAN ENVIRONMENT 34
Abstract ............................................................................................................................. 35
Introduction ....................................................................................................................... 36
Materials and Methods .............................................................................. 38
Site Conditions .......................................................................................................... 38
Soil Testing ................................................................................................................. 39
Rainfall and Moisture Content .................................................................................. 39
Experimental Design ................................................................................................. 40
Shoot Elongation ....................................................................................................... 42
Relative Growth Rate ................................................................................................ 42
Individual Leaf Area ................................................................................................. 42 .
Canopy Development ................................................................................................ 43
Light Interception ...................................................................................................... 44
Visual Assessment ..................................................................................................... 44
Data Analysis ............................................................................................................ 44
Results and Discussion ...................................................................................................... 45
Soil Conditions .......................................................................................................... 45
Survival ..................................................................................................................... 46
Canopy Growth and Development ............................................................................ 46
Canopy Quality ......................................................................................................... 49
Total Canopy Impact ................................................................................................. 52
Shoot Elongation ....................................................................................................... 53
Trunk Growth ............................................................................................................ 55
Leaf Size .................................................................................................................... 57
Inﬂuence of Location ................................................................................................ 59
Conclusion ........................................................................................................................ 60
Tables and Figures ............................................................................................................ 61
Literature Cited ................................................................................................................. 77

vi

INFLUENCE OF INITIAL STOCK SIZE AND EXISITING SOIL CONDITIONS
ON GAS EXCHANGE AND PRE-DAWN MOISTURE POTENTIAL OF TREES

IN THE URBANENVIRONMENT ........................................................... 80
Abstract ............................................................................................................................. 81
Introduction ....................................................................................................................... 82
Materials and Methods ...................................................................................................... 85
Experimental Design ................................................................................................. 85
Photosynthesis, Transpiration, and Stomatal Conductance. .................................... 86
Volumetric Soil Moisture Content ............................................................................. 86
Pre-Dawn Moisture Potential ................................................................................... 87
Analysis ..................................................................................................................... 87
Results and Discussion ...................................................................................................... 88
Photosynthesis, Stomatal Conductance, and T ranspiration ..................................... 88
Inﬂuence of Urban Soils on Tree Physiology ........................................................... 90
Pre-dawn Moisture Content ...................................................................................... 91
Conclusions ....................................................................................................................... 93
Literature Cited ................................................................................................................. 99
APPENDIX ........................................................................................ 101

vii

LIST OF TABLES

Table 1. Studies evaluating annual mortality rates of establishing urban trees. . . . . .23

Table 1-1. Population and 30-year temperature and precipitation within research
communities .......................................................................................... 62

Table 1-2. Baseline measurements of 4.4 cm (1.75 in) bare-root (BR) and balled-and-
burlapped, 5.1 cm (2 in), 6.4 cm (2.5 in), and 7.6 cm (3 in) caliper and canopy volume
planted in four Michigan communities ............................................................ 63

Table 1-3. Soil chemical and physical properties in four communities in Michigan.......64

Table 1-4. F-values of the inﬂuence of size (S), location (L), and time (T) on mean
canopy volume during the ﬁrst two years following transplanting ........................... 66

Table 1-5. Correlation coefﬁcients of the relationship between soil conditions; bulk
density (Bd), pH, cation exchange capacity (CBC), and concentration of calcium (Ca)
with tree growth and canopy development; relative growth rate (RGR), visual assessment
rating (V R), light interception (LI), leaf area (LA), branch growth (BG), and canopy
volume (VOL) across four Michigan communities ............................................. 75

Table 2-1. F-values of net photosynthesis (Pu) and stomatal conductance (Gs) of Autumn
Blaze maple (Acer xﬁeemanii 'Autumn Blaze'), swamp white oak (Quercus bicolor), and
Bloodgood London plane (Platanus x acerfolia 'Bloodgood') the second year aﬁer being
transplanted at four different locations in Michigan ............................................ 95

Table 2-2. Correlation of soil characteristics; bulk density (Bd), pH, cation exchange
capacity (CEC), Calcium concentration (Ca), % composition of sand, % composition of
clay, phosphorous (P) concentration, potassium (K) concentration, and magnesium (Mg)
with transpiration (E) and net photosynthesis (Pn) for June, July, and August across all
locations and species ................................................................................. 96

Table 2-3. F -values for the inﬂuence of size on pre—dawn moisture potentials in June,
July, and August of 2007 at the Lansing, MI locations ........................................ 96

Table 2-4. Mean of pre-dawn moisture potential (w) of Acer xfreemanii 'Autumn Blaze',
Quercus bicolor, and Platanus x acerfolia 'Bloodgood' 1n Lansing, MI from 7/4 to

8/17 ................................................................................................... 97
Table A-1. F -values of cumulative survival percentages of Acer xﬁ'eemanii 'Autumn

Blaze', Quercus bicolor, and Platanus x acerfolia 'Bloodgood' during ﬁrst two years of
establishment in four Michigan Communities ................................................. 102

viii

Table A-2. F-values of the visual assessment rating of Acer xﬁeemanii 'Autumn Blaze',
Quercus bicolor, and Platanus x acerfolia 'Bloodgood' during ﬁrst two years of
establishment in four Michigan Communities ................................................. 102

Table A-3. F-values of relative growth rate of Acer xﬁeemanii 'Autumn Blaze', Quercus
bicolor, and Platanus x acerfolia 'Bloodgood' during ﬁrst two years of establishment in
four Michigan communities ...................................................................... 103

Table A-4. F-values of canopy volume of Acer xfreemam'i 'Autumn Blaze', Quercus
bicolor, and Platanus x acerfolia 'Bloodgood' during ﬁrst two years of establishment in
four Michigan communities ...................................................................... 103

Table A—5. F-values of individual leaf area of Acer x ﬁ'eemanii 'Autumn Blaze', Quercus
bicolor, and Platanus x acerfolia 'Bloodgood' during first two years of establishment in
four Michigan communities ...................................................................... 104

Table A-6. F-values of light interception of Acer x ﬁeemanii 'Autumn Blaze', Quercus
bicolor, and Platanus x acerfolia 'Bloodgood' in four Michigan communities during June,
July, and August 2007 ............................................................................. 104

Table A-7. F-values of shoot elongation of Acer xﬁ'eemanii 'Autumn Blaze', Quercus
bicolor, and Platanus x acerfolia 'Bloodgood' during ﬁrst two years of establishment in
four Michigan communities ...................................................................... 105

Table A-8. Pearson correlation coefﬁcients of visual assessment ratings in relation to
relative growth rate (RGR), light interception (LI), leaf area (LA), branch growth (BG),
and cumulative survival percentage (SURV) from April 2006 to June 2008 ............. 106

Table A—9. Pearson correlation of soil characteristics bulk density (Bd), pH, cation
exchange capacity (CEC), textural composition (% sand, silt, and clay), concentration of
calcium (Ca), phosphorous (P), potassium (K), magnesium (Mg), and visual assessment
ratings (V R) with monthly stomatal conductance (Gs) and net photosynthesis (Pn) of
Acer xﬁ'eemam'i 'Autumn Blaze'. during June, July, and August 2007 .......................... 107

Table A-10. Pearson correlation of soil characteristics bulk density (Bd), pH, cation
exchange capacity (CEC), textural composition (% sand, silt, and clay), concentration of
calcium (Ca), phosphorous (P), potassium (K), magnesium (Mg), and visual assessment
ratings (VR) with monthly stomatal conductance (Gs) and net photosynthesis (Pn) of
Quercus bicolor. during June, July, and August 2007 ........................................ 108

Table A-1 1. Pearson correlation of soil characteristics bulk density (Bd), pH, cation
exchange capacity (CEC), textural composition (% sand, silt, and clay), concentration of
calcium (Ca), phosphorous (P), potassium (K), magnesium (Mg), and visual assessment
ratings (V R) with monthly stomatal conductance (Gs) and net photosynthesis (Pn) of
Platanus x acerfolia ‘Bloodgood’. During June, July, and August 2007 ................... 109

ix

LIST OF FIGURES

Figure 1. Relationship of root and canopy growth of 10.2 cm (4 in) caliper and 25.4 cm
(10 in) trees for 13 years aﬁer transplanting ..................................................... 24

Figure 2. Diagram of root growth of initially smaller and larger trees. . . . .. ..........25

Figure 3. Polynomial regression of the trunk diameter (cm) during the ﬁrst two years of
establishment in large and small caliper studies ................................................ 26

Figure 1-1. Location of research plots within the Emerald Ash Borer Quarantine revised
February, 2008 by the Michigan Department of Agriculture .................................. 61

Figure 1-2. Canopy volume measurements of total height (ho), height of the upper
canopy (ht), middle canopy (hm), lower canopy (hb), height of the origin of the ﬁrst
branch (hi), and the radii of upper canopy (rt), middle canopy (rm), and lower canopy
(rb) .................................................................... 65

Figure 1-3. Canopy volumes of Acer xﬁ'eemanii ‘Autumn Blaze’, Quercus bicolor, and
Platanus x acerfolia ‘Bloodgood’ by size during the ﬁrst two years of establishment. . ..67

Figure 1-4. Inﬂuence of month and size on light interception of Acer xﬁ'eemanii
‘Autumn Blaze’, Quercus bicolor, and Platanus x acerfolia ‘Bloodgood’ pooled across
all locations for June, July, and August of 2007 ................................................ 68

Figure 1-5. Composition of total canopy volume and % change of each species over a two
year period based on initial size classiﬁcation ................................................... 69

Figure 1-6. Mean shoot elongation (mm) of ﬁve branches within the middle canopy of
three species for growth in 2006 and 2007 ...................................................... 70

Figure 1-7. Inﬂuence of initial tree size on relative growth rates of Acer xﬁeemanz’i
‘Auttunn Blaze’, Quercus bicolor, Platanus x acerfolia ‘Bloodgood’ during the ﬁrst two
years of establishment in four Michigan Communities ........................................ 71

Figure 1-8. Inﬂuence of site location on the relative growth rate of Acer xﬁeemam‘i
‘Autumn Blaze’, Quercus bicolor, and Platanus x acerfolia ‘Bloodgood’ during the ﬁrst
two years of establishment ......................................................................... 72

Figure 1-9. Individual leaf size (cm2) of three species during the ﬁrst two years of
establishment in four Michigan communities based on tree size classiﬁcation ............ 73

Figure 1-10. Rainfall deﬁcit, precipitation, and estimated evapotranspiration of (A) Ann
Arbor, (B) Detroit, (C) Lansing, and (D) Rochester Hills, MI from 4/1/2007 to
10/3 1/2007 ........................................................................................... 74

Figure 1-11. Monthly volumetric water content at Ann Arbor, Detroit, Lansing: F enner,
Evergreen, and Mt. Hope locations, and Rochester Hills, MI in 2007 ....................... 76

Figure 2-1. Inﬂuence of initial tree size on pre-dawn moisture potential (-bars) of ﬁve
sizes of Quercus bicolor on 17 August 2007 in Lansing, MI ................................. 98

Figure A-l. Rainfall deﬁcit, precipitation, and estimated evapotranspiration of (A) Ann

Arbor, (B) Detroit, (C) Lansing, and (D) Rochester Hills, MI from 4/1/2006 to
10/31/2006 .......................................................................................... 110

xi

INTRODUCTION:
TREES, PEOPLE, RESTORATION, AND THE URBAN
FOREST

TREES, PEOPLE, RESTORATION, AND THE URBAN FOREST

The Urban Forest

The urban forest is deﬁned in the National Assessment of Our Urban Forest as
“. . .an ecosystem characterized by the presence of trees and other vegetation in
association with people and their developments.” (Dwyer et a1. 2000). This includes all
trees growing in cities and suburban areas with a population density greater than 384
people per square kilometer surrounding a population center of over 50,000 residents
(Dwyer et al., 2000). Current estimates of the national urban forest population conducted
by the United States Department of Agriculture Forest Service are 3.8 billion trees
(Dwyer et a1. 2000 and Nowak et a1. 2001). This resource is increasingly important due
to its economic and environmental impact. Although urban forests are a highly valued
resource providing mediation between the built-environment and the surrounding
ecosystem; it remains relatively understudied (Oke, 1989 and Pauliet and Duhme, 2000).

Humans in metropolitan and urban areas are increasingly dependent upon urban
trees for their social, economic, and environmental beneﬁts (Roberts, 1977). An
estimated 80% of the population of the United States, directly beneﬁt from urban forests
on a daily basis (Dwyer et al., 1999 and Dwyer et al., 2003). Recent efforts to quantify
these beneﬁts (Dwyer et al., 1992; Dwyer and Miller, 1999; McPherson et al., 1999; and
Nowak et al., 2002) have led to increased public awareness of the multitude of beneﬁts it
provides. Furthermore, increased interest in sustainable forest management has solidiﬁed
a link between the urban forest and society (Van Herzele et al., 2005).

Sociological and psychological beneﬁts from tree planting, preservation, and

maintenance are essential components adding to the complexion of a community.

Property value, commercial success, and afﬂuence have been correlated with canopy
cover. In addition, urban forests act as a buffer to mediate the deleterious effects of
human development on the environment. Without trees the negative impact of the built-
environment on the surrounding ecosystems are exacerbated, property values diminish,
and the social beneﬁts of a community are compromised.

Micro-climates formed by tree canopies have been found to moderate surrounding
temperatures (Oke et al., 1989). Energy costs for heating and cooling of nearby
structures can be reduced through shading, light interception, slower localized
windspeeds, and the release of water vapor during transpiration (Oke et al., 1989;
McPherson, 1994). An analysis of Chicago’s urban forest concluded that 70% of the
total energy savings from trees are associated with the shade and reduction in windspeed
associated with mature trees (McPherson, 1994). Annual energy savings of $36 per tree
were formulated for Chicago residents in 1994 (McPherson, 1994) and an average of
30% reduction in cooling costs in Sacramento, California in 1992 during peak
consumption (Akbari et al., 1997). Geographic location, species, age of trees, and
proximity to buildings are factors which inﬂuence the energy savings provided by trees.

Martin et al. (1989) found that residential property values are directly related to
canopy cover. Their study evaluated the inﬂuence of canopy coverage on residential
property values in Dallas, Texas and concluded that trees represent approximately 13% of
the selling price of a home. Further research indicated that neighborhoods that had land
under canopy cover were correlated with higher mean household incomes (Iverson and
Cook, 2000 and Heynen and Lindsey, 2003). In addition to increased property value,

established trees increase the rental rate of commercial ofﬁce buildings (Laverne and

Winson-Geidman, 2003). The aesthetic value and provided shade to the buildings is
attributed with a 7% increase in rental rates.

Trees can also aid in reducing atmospheric pollution. Research conducted by the
United States Forest Service concluded that trees can reduce the amount of ozone, nitrous
oxide, carbon monoxide, and other pollutants (Nowak et al., 2002) in urban areas. There
is increasing interest in the levels of carbon sequestered by the urban forest and its
relative importance in mitigating the possible effects of global climate change (Ip, 1996;
Brack, 2002 ;and Nowak et a1, 2002;). An estimated 700 million tons of carbon are
currently stored in the national urban forest (Dwyer et al., 1999). Furthermore, the urban
forests are responsible for annually sequestering 22.8 tons of carbon (N owak and Crane,
2002b)

The urban heat island effect is considered the most researched anthropogenic
climate modiﬁcation over the last thirty years (Amﬁeld, 2003). Quantifying the ability of
trees to mediate temperatures in urban environments was the central focus of the Chicago
Urban Forest Climate Project (CUFCP) which began in 1990 (McPherson et al.,1997).
Multi-disciplinary research characterized the role of trees in ameliorating effects of
increased temperatures associated with the built-environment. Conclusions suggest that
green spaces associated with building sites can reduce ambient air temperatures by as
much as 3°C (McPherson et al., 1997).

In addition to reducing temperature and improving air quality, trees provide
hydrologic beneﬁts. The initiation of EPA regulations on water runoff further increased

interest in hydrologic beneﬁts provided by urban canopy cover. During rainfall events,

leaves intercept precipitation reducing the intensity and volume of discharge (Dwyer et
al,1992)

Trees provide the social framework for a municipality to have a “sense of
community” with the psychological beneﬁts of a connection between humans and nature
(Ames, 1980 and Dwyer et a1. 1991). An overview of different urban planting initiatives
in Sacramento, California linked group planting projects with positive social interactions
(Sommer et al., 1994). Furthermore, Dwyer et a1. (1991) found that personal
connections with nature had spiritual, emotional, and philosophical importance. Social
and psychological beneﬁts of tree planting are often intangible (Van Herzele et al., 2005),
but are considered essential for community involvement in urban tree programs (Sklar
and Ames, 1985).

In addition to the social importance described by a multitude of researchers; trees
play an integral role in cultures around the world. Festivals are scheduled based on tree
phenology, economically important tree crops are essential components in determining
land use, and some trees have a spiritual or religious connection to their community.
Cristancho and Vining (2004) described species which are highly valued for their
importance to the culture within their eco-region as “cultural keystone species.” The
importance of cultural keystone species provides a substantial contribution to their
conservation and their incorporation in restoration efforts (Joseph and Mansourian,
2005). Furthermore, incorporating cultural principles in restoration efforts goes beyond
the biological needs of the ecosystem.

Beneﬁts provided by urban canopies extended beyond the realm of humans to

include wildlife habitat. Urbanization resulting in changes in land use patterns, often

results in large-scale alteration of previously undeveloped land. Subsequent removal or
ﬁagmentation of ecosystems, result in a decreased abundance of native ﬂora and fauna
(Collinge, 1996 and Zipperer et al., 1997). Even vegetative corridors which are thought
to limit the severity of habitat loss, may have limited success providing a connection to a
more suitable habitat (Collinge, 1996). Therefore, the urban forests are a vital resource
for displaced animal-life and provide the framework for restoration of the ecosystem
affected by urbanization. The function and contribution of the re-vegetated environment
are dependent upon management strategies which can inﬂuence the ability to provide
essential elements for species survival (Zipperer et al., 1997).

A multitude of stakeholders and partners are involved in the planning, planting,
and maintenance of urban forests. Stakeholders are individuals and organizations which
receive direct beneﬁt from the urban forest, without physically contributing to the process
(Brown, 2005 and Jones et al., 2005). Partners are individuals and organizations which
are directly involved in the installation and management of the forest resource. Without
cooperative participation of stakeholders and partners, management of urban forests can
fail and planting efforts can be compromised. It is imperative for urban foresters to
extend their management skills to incorporate personal and ﬁnancial management of the
resources contributed by stakeholders and partners involved in the urban forest (Jones et
aL,2005)

It is essential for urban foresters to involve the community when planning,
installing, and maintaining trees. Management of the many individuals, organizations,
and institutions involved in urban forestry is one of the most challenging and vital roles

of the urban forester (Dwyer and Schroeder, 1994). Conclusions from a survey

conducted by Sommer et a1. (1994), found that trees that were planted with help from
community members were valued more than those planted by municipal foresters. In
addition, forest managers were more likely to receive information about maintenance and
condition of trees planted in association with community members (Sommer et al., 1994).
Research in Oakland, California observed a 60-70% increase in survival of street trees
which included community participation. Sklar and Ames (1985) found that programs
which did not incorporate community involvement in the planning and planting of trees
were failures due to vandalism with close to 100% mortality after six years. Direct
community involvement is essential to the success of maintaining, preserving, and
restoring the urban forest for future generations.
Tree Growth and Development in the Urban Environment

Sup-optimal growth conditions (Berrang, 1985; Oke et al., 1989; and Iles, 2003),
high mortality, and limited life spans of urban trees (Foster and Blaine, 1978) all pose a
threat to continued health of urban forests. A study evaluating Boston’s urban forest
concluded that the life span of an urban tree is limited to as few as ten years (Foster and
Blaine, 1978). Trees in urban environments are subjected to additional stresses when
compared to trees grown in natural forest ecosystems, which limits their growth and
development potential (Roberts, 1977; Kozlowski, 1985; Lauderdale et al., 1995; and
Close et al., 1996). In addition to similar abiotic and biotic pressures present in their
native environment, stress in the urban landscape increase precipitously with human
development (Bassuk and Whitlow, 1986). Anthropogenic stress, such as vandalism, not
normally associated with the natural environment can result in high mortality rates

(Ames, 1985). Added pressure from exotic pests and pathogens further threaten the

tability of the urban forest. Devastation caused by the emerald ash borer in the
Midwestern United States is a testament to the vulnerability of this resource.

A multitude of soil (Craul, 1985; Jim, 1998; and DeKimpe et al., 2000)
atmospheric (Whitlow and Bassuk, 1988; Cregg and Dix, 2001), and environmental
(Kozlowski, 1987 and Oke et al., 1989) causes have been correlated with limited plant
grth in the urban environment (Roberts, 1977; Clark and Kjelgren, 1990; Whitlow et
al., 1992; and Close, 1996). High soil bulk density and degraded soil structure, as a result
of compaction, limit soil water availability for urban trees (J irn, 1998 and DeKimpe et al.,
2000). In addition to reduced inﬁltration from soil compaction, atmospheric drought can
result in decreased plant water potential (Kozlowski, 1987 and Whitlow et al., 1992) and
subsequently suppressed growth. Atmospheric deﬁcits also increase transpiration water
loss, reduce the rate of water absorption by the root system, and reduce net
photosynthesis.

Adverse soil conditions are detrimental to plant health, vigor, and can lead to
premature death. In the urban environment, up to 80% of tree problems are correlated
with poor soil conditions (Patterson, 1980). Soils in urban planting areas are usually
composed of composite materials with little or no organic material, a heterogeneous
texture, and poor structure (Craul, 1992; Jim, 1998; and Dekimpe et. al, 2000). Despite
global research efforts, there still remains a need to further quantify and qualify the
properties of urban soil and their effect on plant physiology (Dekimpe et. al, 2000).

Soil compaction is inherent in urban environments where heavy foot trafﬁc,
human development, and the use of heavy equipment are ubiquitous. Furthermore,

compacted sub-soils required in site construction decrease the space available for root

growth of nearby trees. Soil compaction dramatically alters soil structure and results in
increased bulk density, reduced porosity, decreased permeability, and disrupted soil
aggregation (Hillel et al., 1980; Kozlowski, 1999).

Quantifying of bulk density within urban environments is increasingly important

for soil scientists, urban planners, and municipal arborists (Dekimpe et al., 2000).
Previous research has suggested a bulk density of 1.6 g/ cm3 as the maximum threshold

where root growth is unaffected (Foil and Ralston, 1967, Heilman, 1981; Landon, 1991).
However, soil composition highly inﬂuences the threshold at which plant growth is

limited (Zisa, 1980). A reduction in the rate of root expansion was evident at bulk
densities as low as 1.4 g/ cm3 and 1.8 g/ cm3 for clay and sandy soils respectively (Zisa,
1980). In a survey of urban soils, Jim (1998) observed bulk densities as high as 2.63
g/cm3 along roadsides in Hong Kong. Various remediation methods have been suggested

by Day et al. (1995), however preventing soil compaction is the most effective
management strategy to promote healthy plantings (Kozlowski, 1999).

Reduced porosity as a function of soil compaction is one of the leading causes of
water stress in urban environments (Bassuk et. al, 2001 ). A reduction in micro-porosity
associated with soil compaction reduces the water holding capacity of soil (Zisa, 1980).
In addition, soil compaction affects water ﬂow through the soil proﬁle by reducing the
connectivity of macro-pores which are the driving force for hydraulic ﬂow (Hillel et al.,
1980). Based on rainfall, there is an inverse relationship between soil compaction and
porosity resulting in periods of water logging and extreme drought. This relationship is
further exacerbated by increases in impermeable surfaces from human development.

Berrang et al. (1985) observed widespread water logging leading to decreased tree

growth and death in New York City as a result of limited inﬁltration and runoff ﬁlled
planting pits.

In addition to soil compaction, trees planted in the urban environment typically
have limited rooting area restricted by impervious surfaces (Cregg, 1995). Trees are
often planted along roadsides and in planters where inﬁltration is limited. The necessity
for proper soil volume is directly related to the amount of surface area of the roots in
relation to that of the planting soil (Kozlowski, 1987; Clark and Kjelgren, 1990; and
Whitlow et al., 1992).

Metabolism of essential reactions in root development is inﬂuenced by soil
temperatures. Maximum root growth of trees occurs at temperatures between 17-25" C
(63-77° F). Although temperatures between 50-60° C (122-140° F) are lethal for roots,
soil temperatures approaching this threshold limit their function and subsequently reduce
root grth and water uptake.

Roberts (1977) described chemical stress as the most unique factor associated
with the tree grth in the urban environment. Insecticides, pesticides, herbicides,
fungicides, and growth regulators used for managing the landscape can have signiﬁcant
effects on plant physiology. Furthermore, deicing salt used in temperate climates affect
soil pH and can lead to desiccation of plant material.

Water composes the majority of the fresh weight of trees, is essential for proper
physiological ﬁrnction, and acts as a solvent for gas and mineral exchange to maintain
turgor. Kramer (1987) attributed the role of water stress in tree growth to a water
imbalance between deposits from irrigation and rainfall and withdrawals caused by soil

evaporation and transpiration from the canopy. The balance between water deposits and

10

withdrawals is responsible for delayed growth. Furthermore, alterations in transpiration
during periods of low water potentials are species dependent (Kozlowski and Davies,
1975). Therefore, it is necessary to evaluate several species to validate the effect of water
stress for a given ecosystem. Trees experiencing water stress are more susceptible to pest
infestation (Cregg and Dix, 2001), decreased shoot growth (Close et al., 1996), and
reduced photosynthetic production (Lauderdale et al., 1995).

Indicators of water stress include an overall reduction of tree size, trunk growth,
and individual leaf area. Over 30 years ago, Kozlowski and Davies (1975) postulated
that stomatal closure is the primary factor reducing transpiration in trees experiencing
water stress and suggested that rapid stomatal closure following exposure to increased
light intensity minimizes water loss. Prolonged water stress, referred to as drought stress,
has varying effects on plant growth and development. The primary effects inhibition of
photosynthesis, loss of turgor pressure, and reduction of metabolism of carbohydrates and
nitrogen. Secondary symptoms include a reduction in cell size, and increased stomatal
closure.

Pre-dawn plant moisture potential has also been directly correlated to differences
in soil moisture content (Kozlowski, 1982 and Whitlow et al., 1992). A three year study
of street trees in New York City (Whitlow et al., 1992) suggested that seasonal changes
in pre-dawn plant moisture content was directly attributed to similar changes in soil
moisture content, while trends of midday plant moisture potential were a function of
atmospheric demand. Results further indicated that cumulative water deﬁcits are

prevalent in the Northeastern United States.

11

Status of Michigan’s Urban Forest

The urban forest of Michigan includes a total of 1 11 million trees (Dwyer and
Nowak, 1999) and is considered the epicenter of the emerald ash borer infestation.
Emerald ash borer (Agrilus planipennz‘s), is a phloem boring insect (Haack et al., 2002)
that is responsible for the death of over 30 million ash (F raxz’nus sp.) trees in the
Midwestern United States and Ontario (http://www.emeraldashborer.info/). Originally
identiﬁed in 2002 (Haack et al., 2002), the insect has dramatically altered the species
composition, leaving much of the regional urban forest depleted. Its ability to rapidly
spread is caused by a combination of the abundance of host plants and an ecosystem
integrated within the supply routes of international trade (Poland and McCullough, 2006)
and the distribution of ﬁrewood outside of the quarantine by residents within the
quarantine. Heavily planted due to its stress tolerance and fast growth, F raxinus is a key
genera in the urban forest across a majority of North America. Wide-spread loss caused
by the emerald ash borer infestation represents a signiﬁcant threat to the ecological health
and economic stability of affected communities.

Estimated replacement cost of Michigan’s urban forest is over 71 billion dollars
(Dwyer et al., 2000). As of 2004, Michigan has appropriated over 1 million dollars to
replace over 10,000 dead ash trees (Poland and McCullough, 2006). However, this
represents a small percentage of the trees which have been killed by the emerald ash
borer. Future replacement programs will need to maximize their efﬁciency to properly
restore the depleted canopy. In addition to increasing species diversity to avoid future
epidemics (Bassuk, 1990; Santarnour, 1990; and Poland and McCullough, 2006) it is

essential to provide scientiﬁc evidence on replacement species for inclusion in tree

12

restoration programs, in order to efﬁciently address the need to replant the canopy lost
from the emerald ash borer infestation.
Urban Forest Restoration

Forests are vital to the success of mankind, especially the 60 million people that
are directly dependent on forest resources (Dudley et al., 2005). Conserving,
maintaining, and restoring urban forests is an expensive and intensive process for
municipal foresters. Increasing the number of trees in stable forest communities is offset
by parallel losses in other regions due to human development (Dudley et al., 2005). The
rate of urbanization continues to rise (McDonnell et al., 1997 and Cohen, 2003) and
subsequent removal of native forest ecosystems correlated with urban sprawl remains a
threat to our natural environment (McDonnell and Picket, 1990). In order to retain the
beneﬁts of our forest community, restoration efforts are locally and globally important.
Forest restoration must incorporate ecosystem and landscape orientated goals
(Mansourian et al., 2005).

Ecological restoration is a multi-faceted approach that incorporates needs of
human stakeholders, inhabitants of the ecosystem, and needs of the environment.
Restoration in forestry has taken these needs into strategic planning by recreating habitat
and natural processes disrupted by canopy loss. A set of ecologically derived criteria
based on previous land cover and the needs of the ecosystem was provided by Keddy and
Drummond (1996). Several species types ranging from trees to fungi must be accounted
for in this process. Furthermore, ecological restoration requires a long period of time and

proper planning for success.

13

In conjunction with ecological and culturally sensitive approaches to forest
restoration aimed at preserving the historical and traditional values (N aveh, 2004), it is
imperative to re-establish natural functions in the landscape (Dudley et al., 2005). The
ability to restore a forest based on its function and utility embraces both the needs of
conservation of our forest resource and land development. Understanding the function of
forests prior to development can lead to more sensitive development with less impact on
the forest resource. In addition, restoring the urban forest based on its function can
increase the success of large-scale planting efforts.

The scope of restoration efforts are determined by proper planning, available
ftmding, and the balancing of the needs of all stakeholders involved (Brown, 2005).
Replacing the lost canopy as fast and effective as possible is essential to recover the
numerous beneﬁts that would be lost. Trees represent a signiﬁcant investment in the
community where they are planted. Initial cost of plants, planting, and subsequent
maintenance require ﬁnancial support for municipal forestry departments. An analysis of
our urban forest estimates that each tree has a cost of $640 (Dwyer and Nowak, 1999).

Urban forestry departments are faced with the task of implementing proper
management techniques to enhance establishment of newly planted trees, increase
diversity of species selection, and select proper stock that can grow in sup-optimal
conditions (Dwyer et al., 2003). Several researchers have characterized the success of
urban tree planting programs (Table 1).

Relationships between stock size and post-transplant growth and development are
of particular interest to urban foresters. The relative proximity of the urban forest to the

built-environment increases the importance of analyzing trees in this dynamic

l4

environment. In addition, ﬁrnding for maintenance and installation of urban trees is less
than 1% of the total operating budget for the majority of municipalities in the United
States (Bernhardt and Swiecki, 1993 and Tschantz and Sacamano, 1994). and declined
(Galvin, 1999) as much as 40% between 1986 and 1994 (International Society of
Arboriculture, 1995).

Limited funding provided for large-scale canopy restoration efforts exempliﬁes
the need for proper size selection. Anecdotcal accounts provided by municipal arborists
(Watson, 1985) and limited experimentation in the urban environment (Lauderdale et al.,
1995) indicate that smaller trees establish faster and more successfully than larger trees.
Litzow and Pellett (1982) stated a need for additional research to characterize difference
between tree size and species establishment in urban environments in order to develop
proper size recommendations. Costs and beneﬁts of planting larger trees were reviewed
by the Davey Tree Resources (Davey Resource Group, 2006) as a feasibility study for
large-scale state plantings and the general sentiment of urban foresters was described as,

“Typically, urban tree managers prefer stock 2-3 ” in caliper for planting in their
urban forest, primarily because of the instant tree presence and because vandalism tends
to be reduced on larger caliper trees. But in a SIP (State Implementation Plan) planting,
a budget adequate for large stock is unlikely ”

One of the predominant factors that may limit the success of planting larger
caliper trees in the urban environment is the longer duration of reduced grth associated
with transplant shock. Although there is not a deﬁnitive, single cause of transplant shock
(Watson, 1985), several factors are correlated with delayed or suppressed growth

following transplanting of trees. Genetic variation (Reaves and Whitlow, 2004) , species

15

interactions (Watson etal., 1986), cultural practices (Preaus and Whitcomb, 1980 and
Ferrini et al., 2000), geographic location (Kjelgren and Clark, 1993; Cregg, 1995), site
conditions (Krizek and Dubik, 1987; Vrecenak et al., 1989; Ferrini etal., 2000; and
Cregg and Dix, 2001), time of year (Watson and Himelick, 1982) and stock size (Litzow
and Pellett, 1983; Watson, 1985; Lauderdale, 1995; and Struve et al. 2000) have all been
associated with the severity or duration of water stress trees experience directly after
transplanting.

Post-transplant research correlating initial stock size with suppressed grth has
primarily focused on the hypothesis presented by Watson (1985) that larger trees have a
longer establishment period than smaller trees. A model was formulated based on theory
that root to shoot ratios of larger caliper trees are less than that of smaller caliper trees.
The ratio of the root system to the upper portion (crown/shoots) of the plant it provides
with nutrients and water is referred to as the “root to shoot ratio”. The model formulated
by Watson (1985) suggests that smaller trees have the capacity to outgrow larger caliper
trees when planted at the same time (Figure 1).

This theory is based upon previous conclusions that the roots of larger and smaller
trees grow at relatively the same pace of roughly 45.7 cm (18 in) a year (Figure 2). As
shown in Figure 1, a 25.4 cm (10in) caliper tree may lose upwards of 95% of the root
system when harvested (Watson and Himelick, 1982).Data used to formulate this model
were collected while experimenting with small caliper 10 cm (4 in) and large caliper 25.4
cm (10 inch) trees (Watson, 1985). The root to shoot ratio theory is based on the
comparison of the root system after harvesting to the corresponding shoots outlined by

Watson and Hirnelick (1982).

16

Recent research focused on quantifying the inﬂuence of initial stock size on post-
transplant growth has had conﬂicting results. Data collected by Watson (1985),
Lauderdale (1995), and Gilman et a1. (1998) supports the theory that smaller trees will
surpass the grth of larger trees over time. Conversely, Struve et a1. (2000) concluded
that smaller trees may not outgrow larger trees when production method and genotype
were controlled. A suggested difference in the rate of establishment between larger and
smaller caliper trees is that the healthier more vigorous trees are harvested ﬁrst and the
remaining trees are left in production to be transplanted as large trees. This practice
further confounds the difference in establishment of larger trees due to their pre-disposed
inferiority (Struve et al., 2000). Differences in geographic location, high mortality rates,
species selection, stock size selection, and water availability represent possible reasons
for difference in analyzing establishment rates of different size trees.

Litzow and Pellett (1982) stressed the importance of correlating the conclusions
of previous stock size studies with conditions in the urban environment. Urban
conditions are responsible for as much as 86% variability of tree growth (Vrecenak et al.,
1989) and have been directly correlated with limited growth (Cregg, 1995; Close et al.,
1996; and Jim, 1998). Previous research characterizing the inﬂuence of stock size on
post-transplant grth and development of trees has been limited to controlled conditions
(Struve et al., 1995; Gilman et al., 1998).

There are a multitude of reasons for the variation of results of the studies
conducted by Gilman et a1. (1998), Lauderdale et a1. (1995), Struve et a1. (2002), Watson
(1985), and Litzow and Pellett (1982). Each study focused on different species of trees,

initial size classiﬁcations, cultural practices, sample sizes, and was subjected to different

17

environmental conditions. High mortality rates of the large caliper oaks experienced a
58% loss the ﬁrst year after transplanting (Struve et al., 2002) can confound results.

It is generally accepted that tree species have different grth rates. Therefore,
results correlating tree size and post-transplant growth and development are species
dependent. Previous studies have characterized the effect of size on Acer platanoides
(Litzow and Pellett, 1982), Acer rubrum ‘October Glory’ (Lauerdale et al., 1995),
Quercus rubra (Struve et al., 2002), Quercus virginiana (Gilman et al., 1998), F raxinus
pennsylvanica (Litzow and Pellett, 1982), and T ilia cordata ‘Greenspire’ (Litzow and
Pellett, 1982). Species dependent trends were observed by Litzow and Pellett (1982)
between the linden and maple trees when planted at the same location.

There is a greater difference between the trees used to create Watson’s model
(1985), 10.2 cm (4 in) and 25.4 cm (10 in) caliper than that of the other studies.
Lauderdale et a1. (1995) selected 3.8 cm (1.5 in) caliper trees as the criteria for small trees
and 7.6 cm (3 in) caliper for the larger trees; Struve et a1. (2002) compared 3.6 cm (1.4
in) and 8.4 cm (3.3 in) caliper trees, and Gilman et a1. (1998) studied the differences
between 6.4 cm (2.5 in) and 11.7 cm (4.6 in) trees. Litzow and Pellett (1982) evaluated
several grades of bare-root stock ﬁom 0.91 m (3 ﬁ) whips to 5.1 cm (2 in) caliper.

The inﬂuence of cultural practices on grth and development in the urban
landscape has been the subject of research since the 1970’s (C001, 1976). Differences
between bare-root and balled and burlapped transplant methods has had varying results.
Advancements in transplant technology has led to the ability to successfully transplant
just about any size tree and improved the practice of bare-root transplanting. Research

evaluating the inﬂuence of stock sizes has incorporated a variety of production methods

18

including bare-root branched and whips and transplants (Litzow and Pellett, 1982), balled
and burlapped material (Litzow and Pellett, 1982; Lauderdale et al., 1995; Gilman et a1.
1998)), containerized plants (Gilman et al., 1998; Struve et al., 2002), and tree-spaded
material (Struve et al., 2002).

Limitations of sample size and differences between species limited the impact of
the results found by Litzow and Pellett (1982). Trees larger than the 8’-branched grade
showed a decreased rate of caliper development as size increased and larger sized linden
transplants had a reduced success rate. Although the smaller grade trees may have
established faster, they were also more susceptible to vandalism (Litzow and Pellett,
1982)

Gilman et a1. (1998) found that after 27 months of growth, smaller live oaks
(Quercus Virginia) had a signiﬁcantly greater increase of leader extension (p-value <0.01)
and caliper development (p-value <0.01) than larger trees. The differences in primary
and secondary grth rates indicated that when irrigated the smaller trees were
establishing at a faster rate. At the end of the study, Gilman et al. (1998) observed
similar dimensions of all remaining research trees, and suggested that Watson and
Himelick’s (1982) root to shoot ratio was responsible for the increased rate of
establishment of smaller transplants.

Lauderdale et al. (1995) observed signiﬁcant differences in grth and
development of red maples (Acer rubrum ‘October Glory’) during the ﬁrst two years of
establishment. One years after transplanting, the only statistically differences in growth
between the small and large transplants were recorded for shoot elongation 11.4 and 6.1

cm respectively. In addition to signiﬁcant differences in shoot elongation, after two years

19

height and caliper development were signiﬁcantly greater for the small caliper
transplants. Lauderdale et al. (1995) observed a signiﬁcantly higher percentage of
canopy depletion of larger trees. Only one of the smaller trees experienced a reduction in
canopy while 37.5% of the initially larger trees experienced canopy loss greater than
25%.

Physiological evidence supporting the hypothesis that smaller trees establish at a
faster rate than larger trees was also concluded by Lauderdale et a1. (1995). Smaller trees
had a signiﬁcantly higher (p-value <0.05) photosynthetic rate, suggesting that they were
under less stress. In addition, the smaller trees had higher stomatal conductance
compared to larger trees throughout the experiment with values of .55, 2.18, and 2.31
cm/sec for August of 1993, June of 1994, and August of 1994 in comparison with .30,
1.59, and 1.67 cm/sec of the larger trees. Further evidence of the reduced stress of the
smaller transplants was characterized by lower pre-dawn moisture potentials in August of
1993 and 1994.

Struve et a1. (2002) attempted to limit possible confounding effects of provenance
and variation in nursery production methods. The ratio of canopy volume to root mass
was held constant to investigate differences in growth of different stock sizes. Oak trees
were selected from an identical seed source in order control provenance. Production
methods were controlled to prevent inferior stock from being left in production and later
harvested as the larger trees. Furthermore, all trees were planted into proportionally
accurate planting pits to investigate previous hypothesis suggested by Barnett et a1.
(1983) and Watson and Kupkowski (1991) that differences in growth of smaller and

larger trees was attributed to disproportional planting pit volumes. During the study

20

larger transplants experienced 58% mortality which severely limited the application of
their results. Surviving larger caliper trees had greater trunk grth and height growth
than the smaller trees after a four year period.

Watson (2005) reviewed the inﬂuence of tree size on transplant establishment and
growth. He concluded that there was a deﬁnitive relationship between tree size and rate
of establishment, however the hypothesis that the difference in recovery time will result
in a smaller tree outgrowing a larger tree remained in question. A comparison of the
trunk diameters from the research of Watson (1985), Lauderdale et a1. (1995), and
Gilman et a1. (1998) during the ﬁrst two years of establishment are presented in Figure 3.
In addition, the need for long term research was suggested by Watson (2005).

Summary

Trees are a vital component to humans and their communities. Continued health
and sustainability are essential to retain the economic, social, and environmental beneﬁts
from the urban forest resource. Currently in the Midwestern United States, the emerald
ash borer infestation has re-iterated the importance of diversity within the urban
landscape. Increasing urbanization, high mortality rates, sub-optimal soil conditions, poor
atmospheric quality, and adverse human interaction present serious threats to urban
forests. Efﬁcient management decisions are essential to protect, maintain, and restore
trees in the urban landscapes. Therefore, it is imperative for municipalities to maximize
their return on investment for canopy restoration programs.

Since the inception of urban forestry, research has supported a need to advance
our understanding of the effects of the built environment on tree growth and physiology.

Alterations in the landscape are ubiquitous in urban environments and management

21

strategies rely upon results of ﬁeld research. Anecdotal claims of municipal arborists and
previous work conducted in controlled experiments suggest that smaller trees establish
better than larger trees. The loss of a key genus, ash (F raxinus sp.), prompted a study to
quantify the inﬂuence of initial stock size on grth and development of replacement
species in the urban forest.

The following study was developed to characterize the growth response and
canopy development of four different stock sizes while accounting for site and
environmental conditions in the urban environment. The overall objective is to quantify
the inﬂuence of initial tree size on establishment and subsequent development and
provide recommendations to municipal arborists for increasing the efﬁciency of planting

and canopy restoration programs.

22

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Collinge, SK. 1996 Ecological consequences of habitat fragmentation: implications
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33

CHAPTER ONE

THE INFLUENCE OF INTIAL STOCK SIZE ON TREE GROWTH AND
CANOPY DEVELOPMENT IN THE URBAN ENVIRONMENT

34

THE INFLUENCE OF INTIAL STOCK SIZE ON TREE GROWTH AND
CANOPY DEVELOPMENT IN THE URBAN ENVIRONMENT

Additional key words: Acer x freemanii ‘Autumn Blaze’, canopy volume, light
interception, Platanus x acerfolia ‘Bloodgood’, Quercus bicolor, relative growth rate,
restoration, shoot elongation, and urban soils.
Abstract

There is a need to quantify the inﬂuence of stock size on tree establishment to
maximize efﬁciency of canopy restoration programs in the wake of the emerald ash borer
infestation. Growth and canopy development of three ash replacement species; Autumn
Blaze maple (A cer xfreemaniz' ‘Autumn Blaze’) , Bloodgood London plane tree
(Platanus x acerfolia ‘Bloodgood’), and swamp white oak (Quercus bicolor) of ﬁve
different size classiﬁcations; 4.4 cm (1.75 in) bare-root and balled-and-burlapped, 5.1 cm
(2 in), 6.4 cm (2.5 in), and 7.6 cm (3 in) were recorded during the ﬁrst two years after
planting in four urban communities in Michigan. Canopy volume of maples, oaks, and
7.6 cm (3 in) plane trees declined during the ﬁrst year. Although larger trees maintained
signiﬁcantly larger canopies two years after planting, the rate of canopy development,
trunk growth, and shoot elongation suggest that smaller trees have a better establishment
rate. Canopy dieback was prevalent in larger caliper trees, as a result their total impact
on the planting site was reduced. Existing soil characteristics, in particular bulk density
and pH, exhibited a stronger correlation on canopy development and trunk growth during

the second year than the ﬁrst year following transplanting.

35

Introduction

Large-scale canopy restoration efforts are essential following the wide-spread
death of ash (F raxinus sp.) trees caused by the emerald ash borer (Agrilus planipennis)
infestation. A large portion of trees lost from the infestation were in urban locations
(Poland and McCullough, 2006). The removal of over 30 million ash trees throughout all
forests within the Midwestern United States (www.cmeraldashborerinfo) has placed an
economic burden on several municipal, private, and public forest managers. Operating
budgets for municipal forestry departments are increasingly limited (Galvin, 1999),
therefore it is imperative for municipalities to maximize their return on investment for
canopy restoration programs. The loss of a key genus, ash (F raxinus sp.), prompted a
study to quantify the inﬂuence of initial stock size on growth and development of
replacement species in the urban forest. Current municipal landscape and woodland
ordinances often have replacement speciﬁcations requiring minimum trees sizes of 6.35
cm (2.5 in) for woodland and 7.62 cm (3 in) calipers for landscape enhancement. These
larger caliper trees provide a more substantial impact than smaller caliper trees
immediately following planting, but represent a signiﬁcant investment for municipal
forestry departments due to the higher cost associated with their installation,
maintenance, and potential replacement (Gilman et al., 1998). However, higher
mortality rates (Struve et al., 2000), crown dieback (Lauderdale et al., 1995), and an
extended period of delayed or suppressed growth (Watson, 1985) associated with

transplant shock can adversely affect the impact provided by initially larger trees.

36

Larger trees experience greater transplant shock than smaller trees and the
differences in their establishment rates (Watson, 2005) and subsequent growth has been
the focus of research for over 20 years (Litzow and Pellett, 1982; Watson and Himelick,
1982; Watson, 1985; Lauderdale et al., 1995; Gilman et al., 1998; and Struve et al.,
2000). Watson (1985) postulated that over time smaller trees would surpass the overall
size of large caliper trees and created a model based on differences in root to shoot ratios
of 10.2 cm (4 in) and 25.4 cm (10 in) trees. During harvesting from the ﬁeld, trees lose
as much as 95% of the root system (Watson and Himelick, 1982), subsequently reducing
the ability of the root system to provide adequate moisture and essential nutrients for
proper photosynthetic function and tree growth. This postulation was supported by
Gilman et al. (1998) and Lauderdale (1995), while Struve et al. (2000) suggested smaller
trees will not outgrow larger trees over time. Species differences, geographic location,
high mortality rates, and production methods were thought to be confounding factors in
previous research (Watson, 2005). Litzow and Pellett (1982) suggested that in situ
research quantifying the relationship of initial size and tree growth in the urban
environment would enhance the application of previous reported ﬁndings.

Limited soil moisture availability (Bassuk and Whitlow, 1986), atmospheric
moisture content (Cregg and Dix, 2001), and unique anthropogenic stress (Roberts, 1977)
reduce tree growth and vigor in the urban forest (Close et al., 1996). Increased water
stress, as a result of human activities on soil structure, texture, and composition (Craul,
1985 and Jim, 1998) is thought to be the leading cause of premature mortality of trees in
the urban environment (Patterson et al., 1980 and Bassuk and Whitlow, 1986).

Limitations of root growth caused by compacted soil have been suggested as a factor

37

inﬂuencing the speed of establishment (Watson and Kupkowski, 1991). Understanding
the inﬂuence of site conditions on establishment of different sizes of trees can be used to
guide future planting and replacement efforts.

This study aims to characterize growth response and canopy development
following transplanting of four different stock sizes 4.4 cm (1.75 in), 5.1 cm (2 in), 6.4
cm (2.5 in), and 7.6 cm (3 in) of balled-and-burlapped and one grade of bare-root tree 4.4
cm (1.75 in) while accounting for site and environmental conditions in the urban
environment. Three species; Autumn Blaze maple (Acer xfreemanii ‘Autumn Blaze’),
Bloodgood London plane tree (Platanus x acerfolia ‘Bloodgood’), and swamp white oak
(Quercus bicolor) were planted in four communities af’fected by the emerald ash borer
infestation. The objectives of the study are to 1) quantify the inﬂuence of initial tree size
on establishment and subsequent growth and development, 2) characterize the effects of
the urban environment on tree growth, 3) provide recommendations to municipal
arborists for increasing the efﬁciency of canopy restoration programs, and 4) provide
additional data to test the hypothesis that smaller trees will outgrow larger trees. This
study focused on the ﬁrst two years of establishment and is a collaborative effort among
Michigan State University, the USDA Forest Service, the Michigan Department of
Natural Resources, the Michigan Nursery and Landscape Association, and the municipal
forestry departments of the four corresponding communities.

Materials and Methods
Site Conditions
In April, 2006 three hundred trees were planted in four communities within the

emerald ash borer quarantine area (Figure 1-1 ): Ann Arbor, Detroit, Lansing and

38

Rochester Hills. Sites were identiﬁed in conjunction with individual community forestry
departments. The research plot in Ann Arbor was established at Fuller Park Pool and
Recreation Area adjacent to the University of Michigan Medical Center. In Detroit the
research plot was established at Romanowsky Park, a redeveloped urban site. Three
locations were selected within Lansing; Mt. Hope and Evergreen Cemeteries and Fenner
Nature Center. Trees were planted along roadsides in the cemeteries at Fenner Nature
Center the trees were planted in an open ﬁeld. In Rochester Hills all of the trees were
planted in a 9 m (30 ft) wide trafﬁc median along Hamlin road just south of I-75.
Population and climate data are presented in Table 1-1.
Soil Testing

Twenty soil samples, each consisting of fifteen sub-samples collected from the
top 30 cm (15 inches) of the soil proﬁle at all sites, were analyzed for texture, fertility,
and cation exchange capacity in October of 2007 at the Michigan State University Soil
Testing Laboratory (Michigan State University, East Lansing MI). At the same time 20
soil core samples were collected from each of the Ann Arbor, Detroit, and Rochester
Hills plots to determine the bulk density (Bd) of the existing soil. A total of 50 soil cores
were collected in Lansing based on the heterogeneity of the multiple locations. A
hammer driven soil coring device was used to acquire soil cores, and following oven

drying soil cores for 15 days at 110°C, bulk density was recorded to the nearest 0.01

3

g/cm .
Rainfall and Moisture Content
Rainfall, estimated transpiration (PET), and temperature data were compiled from

the Michigan Agricultural Weather Network. Water deﬁcits were recorded when the

39

inputs from rainfall and irrigation did not account for the water loss from transpiration
and soil evaporation (Kramer, 1987). Ann Arbor, Detroit, Lansing, and Rochester Hills
experienced long periods without a signiﬁcant rainfall events of 22, 22, 39, and 13 days
respectively. The greatest rainfall deﬁcit in 2007 was recorded for the month of July in
Lansing where estimated evapotranspiration was 127 mm greater than rainfall. The
monthly rainfall deﬁcit for July 2007 in Ann Arbor (54 mm) was less than half that of
Lansing. All locations experienced rainfall deﬁcits in June and July. In August the only
site which continued to experience a water deﬁcit was Rochester Hills (59 mm).
Experimental Design

Three species; Autumn Blaze maple (Acer xfreemanii ‘Autumn Blaze’),
Bloodgood London plane tree (Platanus x acerfolia ‘Bloodgood’), and swamp white oak
(Quercus bicolor) were evaluated in this study. In order to reduce variance from
production soils all trees were grown in a common soil type and purchased from Marine
City Nursery (Marine City, MI). Caliper classes and corresponding soil ball sizes are in
accordance with standard sizes based on the American Standards for Nursery Stock
(American Nursery and Landscape Association, 2004). Baseline caliper, canopy volume,
and individual leaf area data were collected in May and June of 2006 (Table 1-2).
Analysis of baseline caliper measurements indicated that the 4.4 cm (1.75 in) bare-root
London plane trees had a signiﬁcantly greater caliper and was similar to the 5.1 cm (2 in)
size classiﬁcation. The 4.4 cm (1.75 in) and 5.1 cm (2 in) balled-an-burlapped oaks had
initial caliper measurements of 6.07 :t 0.13 cm (2.39 i 0.05 in) and 6.34 i 0.16 cm (2.50

i 0.06 in), respectively, and were not statistically different.

40

Tree locations were determined based on the community needs and complete
blocks were not feasible at all four communities. Blocking of trees in Lansing consisted
of ﬁve trees of each species representing all ﬁve size classiﬁcations. The Lansing
location consisted of three sites with 15 Quercus bicolor planted in Fenner Park; 5 Acer x
freemanii ‘Autumn Blaze’ in Mt. Hope; and 25 Platanus x acerfolia ‘Bloodgood’, 10
Quercus bicolor, and 20 Acer x freemanii ‘Autumn Blaze’ in Evergreen Cemetery. All of
the other locations trees were planted in ﬁve randomized complete block designs
consisting of a tree from each size class.

A Michigan State University team (MSU) coordinated and installed 300 trees
using standard professional practice. Prior to installation, all trees were lightly pruned to
remove all dead and potentially conﬂicting branches and the root ﬂare was located within
the root-ball. Bare-root trees were pruned heavier than balled-and-burlapped trees as is
standard practice. In Ann Arbor, a PrenticeTM crane was used to excavate soil from each
planting pit, a BobcatTM skid-steer dug planting pits in Lansing, and an auger was used in
Rochester Hills. After the initial excavation, the MSU team ﬁnished all planting pits and
planting by hand. All planting pits in Detroit were manually excavated and inert material
such as bricks and concrete were removed. Following installation, all trees were mulched
with a 7.6 cm (3 in) layer of municipal woodchips, top-dressed with a ‘/2 cup of 10-20-20
granular fertilizer (LESCO), and well watered.

Subsequent maintenance was conducted by the MSU research team. Bi-weekly
weeding and irrigation of 56.8L (15 US gal) was applied during the 2006 growing season
at all locations. All dead and broken branches were removed throughout the season and

trees were inspected for damage from insects and vandalism. At the end of the ﬁrst

41

growing season all mulch rings were top-dressed with an additional 2.5 to 5 cm (1 to 2 in)
of wood chips to compensate for decomposition. In 2007, trees were not irrigated in
accordance with typical cultural practice of each of the four communities.
Shoot Elongation

Terminal shoot elongation (cm) was measured following leaf abscission in 2006
and 2007. Five branches from the middle-canopy were tagged for identiﬁcation and
measurement. Due to the mortality of a few tagged branches it was necessary to select
some replacement branches within the middle -canopy. In addition, branch caliper (mm)
was collected at the origin of the each tagged branch using a digital caliper (Max-cal,
Fowler, Newton, MA).
Relative Growth Rate

Initial trunk caliper were recorded 15 cm (6 in) above the trunk-soil surface
following planting in May of 2006 using a digital. Recorded caliper measurements were
the average of caliper measurements taken from east to west and from north to south.
Location of caliper measurements were painted to ensure that caliper measurements
collected in October of 2006 and November of 2007 were taken at the identical position.

Relative growth rate was determined based on the trunk cross-sectional area where: rn is
the current radius of the trunk and r ("4) is the radius of the trunk measured the previous
season.

[1] {urnz-nr(n-1)2}/{ mmf}

Individual Leaf A rea

Ten, fully-expanded leaves were collected from the mid-canopy of all trees in

June of 2006, 2007, and 2008. Leaf area (cmz) was measured using a leaf area meter (L1-

42

300C, LI-COR Biosciences, Lincoln, NE) three times and averaged. The average of each
sample was then divided by ten to acquire the average individual leaf area (cmz).
Canopy Development

Crown height and crown width data were collected directly after planting in May
of 2006. Canopies were measured again following leaf abscission in October 2006 and
November 2007. Overall tree height and the width of the lower, middle, upper canopy,
and height of the origin of the ﬁrst branch on the trunk were measured using a measuring
pole. Total canopy (m2) was calculated as the summation of four descending cross-

sectional areas with the following equations:

[2] V1=1/31r(h1-h2)

[31 V2=1/37t(h2-h3)*(1'12+l'11'2+1‘22)
[4] V3=1/31r(h3-h4)*(r22+r2r3+r32)
[51 V4=n 132014-115)

l6] VT: 2(V1 V2 V3 V4)

Where h1=total height, h2=height of the upper canopy measurement, h3=height of the
middle canopy measurement, h4=height of the lower canopy measurement, h5=height of
the origin of the 1St branch, and r1=radius of the upper canopy, r2=radius of the middle
canopy, and r3=radius of the lower canopy (Figure 1-2). Canopy volume was derived
from the summation of additive frustra, or solid sections of a truncated cone and the
contour of the canopy was calculated by additional measurements unlike typical growth

indexes which include height and only two widths (Wright et al., 2006).

43

Light Interception

A quantum line sensor (LI-191, LI-COR BioSciences, Lincoln, NE) was used to
measure the percentage of light intercepted by the tree canopy. Three readings were
recorded and averaged to determine light levels without canopy interference before
measurements were taken underneath each canopy. Three readings were taken 15 cm (6
in) below the ﬁrst branch for each tree at mid-day (1000-14000 h) at each cardinal
direction for a total of twelve measurements. Light interception was calculated as a
percentage of total sunlight averaged from the twelve ﬁgures calculated without canopy
interference.
Visual Assessment

In May of 2007 and 2008, trees were visually inspected and given a rank (scale 1-
5) based on the overall quality of the canopy and amount of branch dieback. A rating of 1
was considered to be a dead or dying tree with major branch dieback or crown mortality,
2 was an unacceptable canopy with over 30.5 cm (12 in) of dieback prevalent within
canopy or some death of major branches, 3 was an acceptable rating for trees that had
dieback present primarily between 20.3 cm (8 in) and 30.5 cm (12 in) in length and very
minor branch dieback, 4 was a fair rating with die-back of 7.6 cm (3 in) and 20.3 cm (8
in), and a rating of 5 was considered good and trees had little to no dieback exceeding
7.6 cm (3 in) .
Data Analysis

Initial analysis indicated signiﬁcant species interactions therefore differences in
growth rates of each species were analyzed separately. Canopy volume, relative growth

rate, shoot elongation, leaf area were analyzed using a repeated measure analysis (Moser

44

and Saxon, 1990) of PROC MD{ED (SAS Inc., Cary, N.C.). Means were separated using
Tukey’s method when signiﬁcant differences were indicated (a=0.05). Analysis of soil
characteristics and environmental conditions were done also using PROC MIXED.

PROC CORR (SAS) was used to determine Pearson’s correlation coefﬁcient
relating soil conditions; bulk density, pH, CEC, volumetric water content, and chemical
compositions with tree growth and development, relative growth rate, change in canopy
volume, leaf area, and shoot elongation. In addition, PROC CORR (SAS) was also used
to correlate the visual ratings in 2007 with light interception, survival, shoot elongation,
and visual ratings in 2008.
Results and Discussion
Soil Conditions

Soil chemical and physical properties varied among locations (Table 1-3). The
main difference in soil textural composition was a lower clay fraction at the Lansing
Fenner, location. The 4 % lower clay fraction may also be responsible for the lower
cation exchange capacity 4.60 meq/100g at this location. A lower percentage of clay in
the soil composition also limits micro-pore space therefore limiting the water holding
capacity of the soil in F enner Park. This difference was most notable in July 2007 when
volumetric water content of the existing soil was more than 7% lower than the clay root
ball.

Mean bulk density (Bd) varied between the soils of each of the locations. The
highest mean bulk density of 1.67 g cm'3 was recorded at Rochester Hills where bulk
densities ranged from 1.51 to 1.84 g cm'3. Fenner, Mt. Hope, and Ann Arbor had the

lowest bulk densities of 1.21, 1.18, and 1.14 g cm'3 respectively. The evergreen cemetery

45

location in Lansing had a soil pH of 6.87. While acidic soils with a mean pH of 6.03
were measured at the Fenner location and the soils collected at Mt. Hope Cemetery,
Detroit, and Rochester Hills were signiﬁcantly more basic with pHs of 7.6, 7.6, and 7.92
respectively.

Survival

During the ﬁrst two years of establishment, annual mortality rates of 1% and
1.5% were recorded for maples and planes respectively. These rates were lower than
those previous observed in other studies of urban tree establishment (Sklar and Ames,
1985; Nowak et al., 1990; Ip, 1996; and Nowak et al., 2004). Maples lost during the
study were the result of vandalism in Detroit. Oaks did not establish as well as the other
two species with an annual mortality rates of 12 and 7.5% in 2006 and 2007.

In general, location and year did not inﬂuence survival of the trees. The higher
mortality rates of oaks were the result of high rates of vandalism at the Detroit location,
and lower soil moisture content at the Fenner location. These results are contrary to the
58% loss of the larger caliper red oaks (Quercus rubra) in the second year of the study
conducted by Struve et al. (2002).

Canopy Growth and Development

Canopy volume increased with caliper size. However, there was no difference in
initial canopy volume between the 6.4 cm (2.5 in) and 5.1 cm (2 in) oaks nor between the
5.1 cm (2 in) and both the bare-root and balled-and-burlapped 4.4 cm (1.75 in) sizes.
Furthermore, the 7.6 cm (3 in) oaks in Ann Arbor had a mean canopy volume of 2.89 m3
(102 ﬁ3), which was greater than all other size classes at Ann Arbor but was smaller than

the mean canopy volume of the 7.6 cm (3 in) caliper trees at all other locations. Initial

46

canopy volume of 7.6 cm (3 in) maples across all locations was 5.66 d: 0.31 m3 (200 d:
10.95 ft3) and larger than all the other sizes. The next largest mean canopy volume was
that of the 6.4 cm (2.5 in) size classes, 3.71 i 0.21 m3 (131 :1: 7.42 ft3), which was only
signiﬁcantly greater than the 4.4 (1 .75 in) sizes. The only London plane tree size
classiﬁcations with similar initial canopy volumes were the 4.4 cm (1 .75 in) balled-and-
burlapped and bare-root.

The inability of a root system to provide adequate moisture to the canopy leads to
an overall reduction in crown volume (Watson, 1985). Wide-spread canopy dieback
during establishment suggests that trees are experiencing transplant shock (Struve et al.,
2002). Prolonged canopy die—back reduces the impact a tree has on the surrounding
landscape. In our study rate of canopy development was signiﬁcantly inﬂuenced by size,
location, and year.

We postulate that differences in response to transplant shock contributed to mean
canopy loss in 2006 and 2007 of oaks and planes at all locations. In 2006, overall mean
canopy volume of oaks declined in Ann Arbor, Detroit, Fenner Park, and Lansing by 9, 3,
9, and 24 % respectively. While the mean canopy volume of oaks in Rochester Hills
increased by 1.5%. In 2007, the only locations which did not continue to experience
volume loss greater than 25% were Detroit and Lansing. The location X size interaction
was signiﬁcant (p-value 0.0002) for oaks in 2007, perhaps as the result of continued
declining canopy volumes of 4.4 cm (1.75 in) bare-root, 6.4 cm (2.5 in), and 7.6 cm (3 in)
oak trees in Lansing by 55, 37, and 5%. The relative magnitude of the inﬂuence of initial
size on canopy volume was lower in 2007 than when the trees were originally planted

(Table 1-4).

47

After the ﬁrst growing season all sizes of maples, oaks, and 7.62 cm (3 in)
London plane trees decreased in canopy volume (Figure 1-3). Lauderdale et al. (1995)
reported severe canopy die back of 7.6 cm (3 in) Acer rubrum ‘October Glory’ during
the ﬁrst two years of establishment. The ﬁrst year after planting, 62.5% of the 7.6 cm (3
in) October Glory maples had lost more than 25% of their individual canopy volume.

In 2007, all sizes of maples and planes increased in canopy volume. Canopy
volume of 4.4 cm (1.75 in) bare-root, 4.4 cm (1.75 in), 5.1 cm (2 in), 6.4 cm (2.5 in), and
7.6 cm (3 in) maples increased canopy volume by 118, 139, 120, 46, and 32% during the
2007 growing season. Mean canopy volume of London plane trees increased by 27, 45,
30, 26, and 13% for increasing size classes in 2007. With the exception of the 4.4 cm
(1 .75 in) bare-root and 5 .1 cm (2 in) sizes, the mean canopy volume of oaks continued to
decline. Swamp white oaks experienced the largest amount of canopy loss, in particular
the larger sized oaks 6.4 cm (2.5 in) and 7.6 cm (3 in) which continued to lose canopy
volume throughout the study (Figure 4). This was a result of a 50% loss of canopy
volume of 7.6 cm (3 in) sizes across all locations and a 17 and 4% increases for the 4.4
cm (1 .75 in) bare-root and 5.1 cm (2 in) sizes.

Larger size classes of maple and plane trees had a greater canopy volume at all
locations. Signiﬁcant location X size interactions were the result of increased canopy
development of the maples in Lansing, Mt. Hope, and Ann Arbor in 2007. However,
Rochester Hills was the only location in 2007 where the larger oaks 6.4 cm (2.5 in) and
7.6 cm (3 in) sizes had a greater mean canopy volume than the other sizes. The lack of

different canopy volumes in oaks reﬂects the model presented by Watson (1985) and

48

provides evidence that smaller oaks are subjected to less growth inhibition than larger
oaks in the urban environment.
Canopy Quality

Measurements of light interception during the 2007 growing season and visual
assessment following bud-break in 2007 and 2008 provided an indication of canopy
quality. Ratings ﬁ'om the visual assessment after bud-break in 2007 were highly
correlated (p-value <0.0001) with light interception, survival, shoot elongation, and
visual ratings in 2008. Trees assessed as poor in 2007 had a reduced individual leaf area
and reduced shoot growth relative to trees of the same species and size with ratings of fair
and good.

Ratings of maples were not inﬂuenced by tree size and the year of assessment.
The only signiﬁcant factor in determining the assessment of the canopy was location (p-
value <0.0001), with the lowest canopy quality of 4.08 at Rochester Hills. Differences in
mean visual assessment of oaks varied by location and size over time (p-values of 0.0009
and 0.0294). Ratings for oaks in Rochester Hills in 2008 were the lowest of all locations
with a rating of 2.65. The largest sized oaks 7.6 cm (3 in) had a mean assessment rating
of 2.1 for 2007 and 2008. The 4.4 cm (1.75 in) bare-root and balled-and-burlapped and
5.1 cm (2 in) sizes had the highest rating in 2007 and 2008. London plane trees were
signiﬁcantly inﬂuenced by the interaction of year and tree size (p-value 0.0004). The
highest visual assessment in both 2007 and 2008 was the 5.1 cm (2.2 in) size
classiﬁcation with ratings of 4.6 and 4.3. The only signiﬁcant differences in canopy
quality based on visual assessment were between the 5.1 cm (2 in) size classiﬁcation and

the 6.35 cm (2.5 in) and 7.6 (3 in) sizes in 2007 and the 7.6 cm (3 in) size in 2008.

49

Many of the beneﬁts provided by the urban canopy are the result of shade or the
percentage of light intercepted by the canopy (McPherson et al., 1997 and Nowak et al.,
2002). Reductions in temperature (McPherson, 1994), rainfall intensity (Dwyer et al.,
1992), and windspeed (Oke, 1989) are enhanced by the quality of the canopy. Periodic
defoliation is a symptom of transplant shock (Struve and Joly, 1992) and when trees are
defoliated their impact is compromised. Additional water and nutrients are required for
the canopy to “re-ﬂush” following the loss of leaves. The process of re-foliation
adversely affects trunk growth, and the loss of foliage adversely impacts radial growth
(Rose, 1958) and can lead to mortality (Kulman, 1971 and Dobbertin, 2005).

Initial tree size inﬂuenced the amount of light intercepted by the canopy for all
species in June and July, but was only a signiﬁcant factor in determining the light
interception of maples in August (Figure 1-4). In June, the 4.4 cm (1 .75 in) bare-root size
which only intercepted 51% of light while all other sizes intercepted more than 10% more
light. All sizes of maples intercepted less light in July than in June. In August both the
4.4 cm (1 .75 in) and the 5.1 cm (2 in) size class increased the percentage of light
interception. Larger caliper 6.4 cm (2.5 in) and 7 .6 cm (3 in) trees intercepted 67 and
64% in July and close to 60% in August. The only size which did not intercept a similar
amount of light in August was the 4.4 cm (1 .75 in) bare-root size.

In June of the 7.6 cm (3 in) sized oaks indicated signiﬁcantly less light
interception than the 4.4 cm (1 .75 in) and 5.1 cm (2 in) balled-and-burlapped trees. The
larger oaks intercepted 37% of light while the 4.4 cm (1.75 in) and 5.1 cm (2 in) balled-
and-burlapped trees intercepted 57 and 62% of light in June respectively. In August the

amount of light intercepted by the canopy did not differ by size (p-value .5093).

50

Shade provided by London plane trees was directly inﬂuenced by initial size
classiﬁcation in June and July. In June, the 4.4 cm (1 .75 in) trees intercepted 40% of
light which was the lowest amount of interception among all the sizes. All size classes
experienced a reduction in canopy cover between June and July (Figure 1-7). There was
no longer a difference in the amount of shade provided across size classes in August.

Site location inﬂuenced the quantity of light intercepted for all species in June and
July. In August, the amount of light intercepted by maples and planes was signiﬁcantly
inﬂuenced by site location (p-values of 0.0075 and <0.0001). Maples in Rochester Hills
intercepted 10% less light than trees at all of the other locations. Mt. Hope was the only
location where there was no evidence of defoliation and light interception went from 70
to 72% from June to July. Other locations all experienced a decline in the amount of
light intercepted, however, maples at the Lansing Evergreen and Detroit location
continued to intercept more light than those in Rochester Hills. In August, the only
location which still intercepted signiﬁcantly more light than Rochester Hills (47%) was
Lansing (61%).

The amount of light intercepted by oak trees in June was signiﬁcantly greater at
Ann Arbor (61%) than at Rochester Hills (42%). A reduction in light interception was
recorded for oaks at all locations, and the greatest difference in mean light interception
was observed at Lansing where the amount of light intercepted went from 54% to 36%.
In July, oaks across all sizes at Fenner and Ann Arbor intercepted signiﬁcantly more light
than in Rochester Hills. By August there was no longer a difference in light interception

between all sizes of oaks.

51

London plane trees in Ann Arbor, Detroit, and Lansing intercepted 63, 55, and
67% of light, while planes in Rochester Hills only intercepted close to 30%. The
signiﬁcantly lower percentage was perhaps a result of defoliation in the previous year
which limited the capacity of the trees to refoliate in 2007. The percent of light
intercepted by planes in Lansing was signiﬁcantly greater than Rochester and Ann Arbor
in July, and all other locations in August. These differences were most likely attributed
by the ability of planes in Lansing to refoliate in August while defoliation continued to
decrease the amount of light intercepted at all other locations.
Total Canopy Impact

The limitations of removing dead trees from statistical analysis when evaluating
the differences in tree size evaluations can confound conclusions about the impact of a
size class which may have high mortality rates. Therefore, a canopy volume ratio in
relation to the total volume of species was calculated for each size class, which
incorporated the inﬂuence of mortality (Figure 1-5). The ratio incorporates the
differences in canopy volume due to canopy dieback and mortality. Results from this
analysis provide the relative value of the impact provided by planting larger trees.

Total canopy volume of maples, oaks, and planes planted in April 2006 was 297
(10, 488 113), 234 (8, 263 113), and 470 m3 (16,5 97 113). Initially the majority ofthe
canopy volume was provided by the larger caliper trees (Figure 1-5). Net canopy volume
planted in 2006 was 1,001 m3 (35, 350 113) which decreased during the 2006 growing
season by 81 m3 (2, 860 ft3) then in 2007 the cumulative canopy increased to 1,048 m3
(3 7, 010 if). The contribution of smaller trees to the cumulative total canopy increased

for maples, oaks, and planes after the ﬁrst two years of establishment. Canopy dieback,

52

mortality, and lower rates of canopy development reduced the impact of 7.62 cm (3 in)
caliper maples, oaks, and planes by 18, 34, and 9% during the ﬁrst two years of
establishment (Figure 1-5). In contrast, the relative impact of smaller caliper trees
increased in 2007 for all three species. Increases of 4.8 and 2.3% were measured for the
contribution of the 4.4 cm (1 .75 in) bare-root and 5.1 cm (2 in) maples respectively.
While the inﬂuence of the largest caliper and 4.4 cm (1 .75 in) bare-root sizes of London
plane trees decreased. The 7.6 cm (3 in) oaks had the largest drop in total canopy volume
by nearly 20%. Conversely the total canopy volume of 5.1 cm (2 in) size class oaks
increased by close to 7.5 %. The composition of London plane trees was not as dynamic
as the maples and oaks. During the ﬁrst two years of establishment the percent
composition of the total canopy volume provided by the largest sized 7.6 cm (3 in)
caliper maples, oak, and planes decreased by and 6.7, 19.5, and 3.5%, respectively.

Extrapolation of the ratio, can guide future size selections of Acer xfreemanii
‘Autumn Blaze’, Quercus bicolor, and Platanus x acerfolia ‘Bloodgood’ in canopy
restoration programs. Over time the impact of different caliper trees can be measured by
their contribution to the total canopy volume planted at a location. Optimal sizes can be
selected based on their ratio of canopy development. For instance, it would be more
efﬁcient to plant a 4.4 cm (1.75 in) oak than a 7.6 cm (3 in) oak which had a reduction of
20% in its contribution to the total canopy volume across all locations.
Shoot Elongation

Shoot elongation for each species was signiﬁcantly inﬂuenced by location and
size in 2006 and 2007 (p-values <0.0001), and the interaction between size and location

was only signiﬁcant for maples in 2006 (p-value 0.0012) (Figure 1-6). Overall shoot

53

elongation of maples signiﬁcantly increased after the second year (p-value <0.0001) by
nearly 3 fold. Mean shoot elongation of oaks decreased ﬁ'om 66 (26) to 55 cm (22 in)
and the Bloodgood London plane trees did not differ between 2006 and 2007 (p-value
0.6008). In 2006, 4.4 cm (1.75 in) balled-and-burlapped and bare-root plane trees had
nearly double the shoot elongation (19.6 and 17.0 cm) than all the size classes combined.
Mean shoot elongation of the 4.4 cm (1 .75 in) size London plane trees declined from 17
cm in 2006 to 14.3 cm in 2007. The 7.6 cm (3 in) balled-and-burlapped plane trees had
signiﬁcantly less shoot growth (7.3 cm) than smaller caliper 4.4 cm (1 .75 in) bare-root
and balled-and-burlapped sizes in 2007. Initial tree size inﬂuenced shoot elongation in
2006 for all species and for maples and plane tree in 2007.

Elongation of terminal shoots is an important indicator of tree establishment
(Watson et al., 1986 and Struve et al., 2000). Species dependent responses of twig growth
in response to transplant shock were presented by Watson et al. (1986), with a reduction
in growth lasting an average of three years. Results of the inﬂuence of initial size of
Quercus bicolor were consistent with the previous evaluation of Quercus rubra (Struve et
al., 2000). They observed similar shoot elongation of transplanted and non-transplanted
oaks the ﬁrst year after planting, however a reduction in shoot extension in transplanted
red oaks occurred the second year after planting. Larger caliper oaks had more than
twice the shoot elongation relative to smaller oaks the ﬁrst year after transplanting, while
over the next two years smaller trees had signiﬁcantly greater stem growth (Struve et al.,
2000)

The inverse relationship was reported by Lauderdale et al. (1995) when

comparing the stem elongation of 3.8 cm (1.5 in) and 7.6 cm (3.0 in) Acer rubrum

54

‘October Glory’. Smaller trees doubled the amount of shoot elongation from 11.4 cm
(4.5 in) to 22.4 cm (8.8 in) while the shoot elongation of the larger trees decreased from
6.1 to 5.5m. A reduction in shoot elongation over an extended period of time indicates
that the root system of the smaller trees are establishing at a faster rate (Lauderdale et al.,
1995). In 2006, mean shoot elongation of the 4.4 cm (1.75 in) bare-root and balled-and-
burlapped maples were 9.7 (3.8) and 6.9 cm (2.7 in) respectively. Mean shoot elongation
of these size classes was nearly triple that of the 6.4 cm (2.5 in) and 7 .6 cm (3 in) sizes
with means of 2.3 and 2.8 cm of growth. Unlike the previous study by Lauderdale et al.
(1995) the mean shoot elongation of the larger caliper 6.4 cm (2.5 in) and 7.6 cm (3 in)
maples did not decrease in 2007, however they remained signiﬁcantly less than the mean
shoot growth of the 4.4 cm (1.75 in) balled-and-burlapped size classiﬁcation.
Trunk Growth

Trunk growth of maples, oaks, and planes was inﬂuenced by size (p-values of
<0.0001, 0.001, and <0.00001) and year (p-values of <0.0001, 0.0006, and <0.0001).
During our study, location signiﬁcantly inﬂuenced the trunk growth of maples (p-value
<0.0001) and planes (p-value <0.0001), and the only time when the location X size
interaction was signiﬁcant was for maples in 2006. Trunk growth was characterized by
differences in the relative growth rate to account for increased trunk cross-sectional area
rather than caliper (Figure 1-7). Maples, oaks, and planes increased relative grth rates
from 0.07, 0.05, and 0.10 in 2006 to 0.20, 0.01, and 0.18 in 2007.

Differences in trunk growth among size classiﬁcations indicate different
responses to transplant shock. Differences between smaller and larger caliper trees were

reported for oaks, maples, and planes in both 2006 and 2007 (Figure 1-7). The 4.4 cm

55

(1 .75 in) bare-root and 5.1 cm (2 in) trees had greater trunk growth than the 7.6 cm (3 in)
trees which had the lowest relative growth rate of 0.04. Relative growth rate of both
bare-root and balled-and-burlapped 4.4 cm (1 .75 cm) maple trees was greater than all
other size classes in 2006. Relative growth rates of the 4.4 cm (1.75 in) bare-root and
balled-and-burlapped sized maple trees were 0.29 and 0.27 in 2007. After the ﬁrst two
years of establishment, the larger caliper 6.4 cm (2.5 in) and 7.6 cm (3 in) sized trees had
the least amount of trunk growth with relative growth rates of 0.12 and 0.11.

Smaller caliper size classiﬁcations having a greater relative growth rate was
consistent with the results found in the London plane trees. In 2006, the 4.4 cm (1 .75 in)
size planes had a relative growth rate of 0. l 6 and 0.11 for the balled-and-burlapped and
bare-root size classes, respectively, and were signiﬁcantly greater than the mean relative
growth rate of the 6.4 cm (2.5 in) size. The trend of smaller caliper trees having a greater
relative growth rate continued in 2007, when the 6.4 cm (2.5 in) and 7.6 cm (3 in) had
relative growth rates three times less than that of the mean relative growth rate of the 4.4
cm (1 .75 in) balled-and —burlapped trees. The trend was not as apparent for oak trees.
Different sized oaks had similar growth rates in 2006, however in 2007 there were
signiﬁcant differences between the initial sizes. The 5.1 cm (2 in) oaks had a mean
relative growth rate of .13 which was greater than the .04 relative growth rate of the 7.6
cm (3 in) size.

Location signiﬁcantly inﬂuenced maples and planes, however it was not a factor
in determining the relative growth rate of oaks (Figure 1-8). In 2006 the relative growth

rate of maples in Lansing (0.12) was signiﬁcantly greater than all the other locations.

56

Similarly the relative growth rate of planes was greater in Lansing than all locations
except Ann Arbor in 2006 and all locations in 2007.
Leaf Size

Leaf size decreases when water is limiting and is an important indicator of
transplant stress (Parkhurst and Loucks, 1972). Individual leaves differed by initial tree
size, year, and the interaction of size and year for all three species of trees. Location only
inﬂuenced the mean leaf size of maples (p-value <0.0001). Mean leaf size of maples,
oaks, and planes increased after the ﬁrst year of establishment by 85, 95 and 57%
respectively. Mean leaf size in Rochester Hills was 26.8 cm2 (4.15 inz), 42.1 cm2 (6.52
inz), and 25.1 cm2 (3.89 inz) in 2006, 2007, and 2008. In 2008, mean leaf size of maples
in Rochester Hills was less than in 2006, perhaps as a result of increased water stress in
2007. The 40% reduction in leaf size in 2008 at Rochester Hills corresponded to the
location with the least conducive soil conditions.

Mean individual leaf area increased for all three species from 24.8 (3.8), 32.9
(5.1), and 37.5 cm2 (5.8 inz) in 2006 to 45.8 (7.1), 64.1 (9.9), and 58.7 cm2 (9.1 inz) in
2007 for maples, oaks, and planes. We postulate that the increase in leaf size is the result
of root expansion during the ﬁrst year and the ability for the new root system to provide
more water and nutrients to the crown developing in 2007. The reduction observed in
2008 in consistent with the ﬁndings of Struve and Joly (1992) which observed a
reduction in leaf size as a response to transplant shock in red oak (Quercus rubra)
seedlings.

In 2008, the mean leaf size of 6.4 cm (2.5 in) and 7.6 cm (3 in) maples were

signiﬁcantly smaller than the 4.4 cm (1 .75 in) balled-and-burlapped and bare-root sizes

57

(Figure 1-9). In 2006, the mean individual leaf area of the bare-root London plane trees
was 70.9 cm2 more than twice the size of any other size class. In 2007, the leaf size of
the bare-root London plane trees remained signiﬁcantly larger than the rest of the sizes,
and the 4.4 cm ( 1.75 in) and 5.1 cm (2 in) sizes had larger leaves than the 6.4 (2.5 in) and
7.6 cm (3 in) sizes, perhaps as a response to the heavier pruning they received before
planting. However, in 2008 the mean leaf size only for the 4.4 cm (1.75) bare-root and
balled-and-burlapped trees were 78.6 (12.2) and 63.8 cm2 (9.9 inz) remained signiﬁcantly
larger than the 7.6 cm (3 in) size which had a mean of 45.2 cm2 (7.0 m2).

The bare-root oaks had a mean leaf size of 22.3 cm2 (3.5 in2)in 2006 which was
signiﬁcantly less than all other size classes. In 2007 size was not a signiﬁcant factor in
determining leaf size (p-value .2399). In 2008, the 4.4 cm (1 .75 in) bare-root trees and
5.1 cm (2 in) sizes had respective leaf sizes of 70.4 (10.9) and 57.8 cm2 (9.0 in2)which
were both greater than the 36.1 cm2 (5.6 inz) leaf size of the 7.6 cm (3 in) size. The
dramatic change in leaf size of the 4.4 cm (1 .75 in) bare-root trees was the result of the
death of the three trees within the size classiﬁcation after the ﬁrst year.

Tree size inﬂuenced the individual leaf area of maples collected in 2008 (p-value
0.0006). The second year after transplanting, the smaller 4.4 cm (1 .75) bare-root and
balled-and- burlapped tree sizes had a mean leaf size of 40.8 (6.3) and 38.3 cm2 (5.9 inz)
respectively. Leaf size of the larger sized maples of 6.4 (2.5 in) was 31.5 cm2 (4.9 inz)
and 7.6 cm (3 in) caliper was 28.2 cm2 (4.4 inz) both of which were signiﬁcantly smaller

than the smaller caliper trees.

58

Inﬂuence of Location

Differences in growth and canopy development at each of the corresponding
communities were best exempliﬁed by variation of their soil composition (Table 1-3) and
rainfall deﬁcits (Figure 1-10), which affected soil volumetric water content (Figure 1-11).
Results from our correlation analysis (Table 1-5) indicate that soil bulk density, pH, and
calcium concentration were all highly correlated with differences in canopy growth and
development during establishment. Bulk densities as high as 1.86 g cm'3 30.46 g in'3
were reported at Rochester Hills, which is much greater than the 1.6 gem"3 26.21 g in'

3 threshold at which root growth is limited (Zisa, 1980). Reductions in the rate of root
development adversely affect the ability of a tree to uptake water even when there is
adequate soil moisture present (Watson and Himelick, 1982). Furthermore high calcium
concentrations (2626) ppm and a mean soil pH of 7.92 contributed to the lower growth in
comparison to the other locations.

In 2006 relative growth rate was negatively correlated with pH and calcium
concentration and in 2007 was also correlated with bulk density and cation exchange
capacity (Table 1-3). Canopy development was unaffected by soil conditions in 2006,
while in 2007 canopy development bulk was highly correlated with density, pH, cation
exchange capacity, and calcium concentration. The reduced rate of canopy development
observed at Rochester Hills was the highly correlated with of greater bulk density and
elevated pH. Without supplemental irrigation in 2007 the correlations between soil

conditions and canopy and trunk growth were exacerbated (Table 5).

59

Conclusion

Differences in soil composition at each location primarily bulk density, pH, and
calcium concentration, were found to have signiﬁcant negative correlations with tree
growth in 2007. The lack of, and inability for root systems of larger trees to supply the
canopy with water was characterized by decrease light interception of the trees in July of
2007 at all locations and further exempliﬁed the differences in establishment rate of
larger vs smaller trees.

Results ﬁom the study indicate that there is a deﬁnitive relationship between tree
size and canopy growth in development in the urban environment. Over the course of the
study overall canopy volume of larger trees generally remained greater than the smaller
trees, however, differences in rate of canopy development, branch growth, and relative
growth rate suggest that smaller trees appear to have a minimized duration of transplant
shock in comparison larger trees. In addition, the canopy composition of total canopy of
each species indicates that smaller maples and oaks provide are a more substantial
component two years after planting. Subsequent data will provide more evidence to
evaluate the postulation of Watson (1985) that smaller trees outgrow larger trees over
time. Our study emphasizes the need for municipal arborist to take initial size into

consideration in future canopy restoration programs.

60

Tables and Figures

   

I Level |

Level"

Level III

Research Plot

 

Figure 1-1. Location of research plots within the Emerald Ash Borer
Quarantine revised February, 2008 by the Michigan Department of
Agriculture.

61

Table 1-1. Population and 30-year temperature and precipitation within research

 

 

communities
Highest Lowest
Monthly Mean N12123:), Annual
Municipality Population Temperature Precipitation
(July) Temperature
(January)
°C °F °C °F mm In
Ann Arbor 114,498 22.7 72.9 -4.6 23.8 872.0 35.3
Detroit 911,402 22.8 73.1 -4.8 24.3 833.4 32.8
Lansing 118,379 21.6 70.9 -5.6 21.9 800.6 31.5
Rochester 68,754 22.6 72.6 -4.9 23.2 765.8 30.2

Hills
All population data collected from United States Census Bureau 2003 Estimates
Weather data collected based on 30-yr means from 1971-2001
Ann Arbor, Detroit, and Lansing weather information collected from weather stations within each
city
Weather data for Rochester Hills was the average of data collected in Pontiac and Shelby Township

62

Table 1-2. Baseline measurements of 4.4 cm (1.75 in) bare-root (BR) and balled-
and-burlapped, 5.1 cm (2 in), 6.4 cm (2.5 in), and 7.6 cm (3 in) caliper and canopy
volume planted in four Michigan communities

 

 

 

 

Species Size Caliper (cm) Caliper (in) _C_anopv Volume
Acer xfreemanii (pi)
'Autumn Blaze'
BR x5.10 i 0.07 d 2.01 i 0.03 d 1.44 :t 0.17 c
1.75 4.99 i 0.10 d 1.97 i 0.04 d 1.91 i 0.32 c
2 5.89 i 0.08 c 2.32 :t 0.03 c 2.14 i 0.12 c
2.5 6.34 d: 0.08 b 2.49 i 0.03 b 3.71 :1: 0.21 b
3 7.43 i 0.08 a 2.93 d: 0.03 a 5.66 :1: 0.31 a
Quercus bicolor
BR 4.76 d: 0.14 d 1.87 i 0.06 d 0.54 :1: 0.07 c
1.75 6.07 i 0.13 c 2.39 :1: 0.05 c 1.19 :t 0.11 c
2 6.34 i 0.16 c 2.50 i 0.06 c 1.33 :t 0.07 b
c
2.5 7.05 d: 0.12 b 2.77 :t 0.05 b 2.04 i 0.10 b
3 9.15 i 0.18 a 3.60 d: 0.07 a 6.64 i 0.72 a
Platanus x
acerfolia
'Bloodgood'
BR 6.28 d: 0.15 c 2.47 i 0.06 c 2.34 i 0.18 d
1.75 5.07 i 0.13 d 1.99 i 0.05 d 2.28 :1: 0.24 d
2 6.53 i 0.09 c 2.57 :t 0.03 c 3.61 d: 0.25 c
2.5 8.07 d: 0.12 b 3.18 :1: 0.05 b 6.36 :t 0.32 b
3 8.65 i 0.10 a 3.41 i 0.04 a 8.93 d: 0.45 a

 

Xmeans separated within columns of each species using Tukey's adjustment (a=0.05)

63

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64

 

 

AL

AK

 

AL

 

 

 

 

STANDARDIZED )—»

 

Figure 1-2. Canopy volume measurements of total height (h), height of the upper
canopy (ho, middle canopy (hm), lower canopy (hb), height of the origin of the ﬁrst
branch(h;), and the radii of upper canopy (rt), middle canopy (rm), and lower canopy

(rb)

All measurements standardized 6 inches above the root-soil surface interface
Measurements were taken from east to west and from north to south and averaged

65

Table 1-4. F-values of the inﬂuence of size (S), location (L), and
time (T) on mean canopy volume during the ﬁrst two years
following transplanting

 

Maples gags Planes
S 119.92 *** 86.33 *** 151.07 ***
L 10.82 *** 4.80 ** 18.76 ***
T 156.84 *** 18.76 *** 41.31 ***
SxL 2.40 ** 3.83 *** 2.87 **
SxT 0.74 NS 15.13 *** 0.56 NS
LxT 16.84 *** 0.89 NS 25.71 ***
SxLxT 1.94 ** 1.07 NS 1.36 NS

 

*,**,*** represent signiﬁcance with p-values of 0.05, 0.01, and <0.0001
respectively

66

 

Acerx freemanii 'Autumn Blaze'

......

 

. iii:
Quercus bicolor

Canopy Volume (m3)

as“?
'5 P: _ l

 

‘
u‘
\31

12 . Platanus x acerfolia 'Bloodgood'

 

 

o .
— Baseline
22:3 2006
— 2007 Initial Size

Figure 1-3. Canopy volumes of Acer xfreemanii
‘Autumn Blaze’, Quercus bicolor, and Platanus x
acerfolia ‘Bloodgood’ by size during the ﬁrst two years of
establishment

BR 1.75 2 2.5 3

67

 

 

0.9 l Acerx freemanii 'Autumn Blaze'
0.8 -
0.7 «
0.6 4
0.5 .
0.4 -
0.3

 

0.6 .
0.5 -
0.4 -

Light Interception (%)

0.3 -

 

0.7 -
0.6 -
0.5 ~
0.4 -

0-3 ‘ i: 13.3.
0.2 ~ I

+3
0.1

 

 

 

 

June July August

Figure 1-4. Inﬂuence of month and size on light interception of Acer xﬁeemanii
‘Autumn Blaze’, Quercus bicolor, and Platanus x acerfolia ‘Bloodgood’ pooled
across all locations for June, July, and August of 2007

BR represents the 4.4 cm (1.75 in) bare-root initial size

68

 

Acer x freemanii 'Autumn Blaze'

30‘

20‘

10

 

 

 

 

 

O . i.—
40 Quercus bicolor
60 -

Composition (%)

 

 

 

-40
PI rf ' ' '
_ Initial atanus x ace olIa Bloodgood
4O . [3:] 2007
- change

 

 

 

 

 

 

 

 

 

l I

1.75 BR 1.75 2 2.5 3

Figure 1-5. Composition of total canopy volume and % change of
each species over a two year period based on initial size classiﬁcation

BR represents the 4.4 cm (1.75 in) bare-root initial size

69

250

 

Acer x freemanii 'Autumn Blaze

200-
150-
100‘

01
O

  
   
   

 

O

Quercus bicolor

_\
030
00

.b
0

Shoot Elongation (mm)
M O)
O O

O

 

Platanus x acerfolia 'Bloodgood

 

 

200 -
150 -
100 -
5O -
BR 175 2 2'5 3— 2006
Initial Size 2007

Figure 1-6. Mean shoot elongation (mm) of ﬁve branches
within the middle canopy of three species for growth in
2006 and 2007

70

 

Acer x freemanii 'Autumn Blaze'

 

Quercus bicolor

P
_\
0

.°
c
a:

 
  

Relative Growth Rate

Platanus x acerfolia 'Bloodgood'

 

 

o
.°.°.°.°b
Anon-ho

  

 

 

   

P
c

BR 1.75 2 2.5 3
—2006

Size Classiﬁcation 2007
Figure 1-7. Inﬂuence of initial tree size on relative growth rates of Acer x

freemanii ‘Autumn Blaze’, Quercus bicolor, Platanus x acerfolia ‘Bloodgood’
during the ﬁrst two years of establishment in four Michigan Communities

Relative growth rate is the increase of trunk cross sectional area divided by initial trunk cross
sectional area

71

Relative Growth Rate

 

 

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72

 

60

Acer x freemanii 'Autumn Blaze'

 

80 - Quercus bicolor

Individual Leat Area (cm‘)

 

Platanus x acerfolia 'Bloodgood‘

_ Baseline
30 J -.- 2006
_ 2007

 

 

 

BR 1 .75 2 2.5 3
Slze Classiﬁciation

Figure 1-9. Individual leaf size (cm2) of three species
during the ﬁrst two years of establishment in four Michigan
communities based on tree size classiﬁcation

73

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74

Table 1-5. Correlation coefﬁcients of the relationship between soil
conditions; bulk density (Bd), pH, cation exchange capacity (CBC), and
concentration of calcium (Ca) with tree growth and canopy development;
relative growth rate (RGR), visual assessment rating (VR), light
interception (LI), leaf area (LA), branch growth (BG), and canopy
volume (VOL) across four Michigan communities

Bd pH CEC Ca
RGRl -0.089 NS -O.l48 * -0.121 NS 0135 *
RGR2 -0.144 * -O.358 *** -0342 *** -0370 ***
VR -0154 ** -0.071 NS 0019 NS -0054 NS
ALI] 0.122 * 0.052 NS 0.026 NS 0.034 NS
AL12 0.177 ** 0.080 NS -0012 NS 0001 NS
ALA 0.043 NS 0.093 NS 0.1 16 NS 0.123 *
ABG 0.137 * 0.096 NS 0.091 NS 0.106 NS
AVOLl -0.071 NS -0059 NS -0.066 NS -0.058 NS
AVOLZ -0242 *** -0.276 *** -0244 *** -0253 ***

 

*, **, and *** represent signiﬁcance with respective p-values of $0.05, 50.01,
50.0001

75

Volumetric Soil Content (%)

 

 
 

 

 
 

 

 

 

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Literature Cited

American Standards for Nursery Stock. 2004. American Nursery and Landscape
Association. Washington, DC.

Bassuk, N., and T. Whitlow. 1986. Urban stress in not limited to people. American
Nurseryman. 163:57-61

Close, R.E., Nguyen, P.V., and J .J . Kielbaso. 1996. Urban vs. natural sugar maple
growth: I. Stress symptoms and phenology in relation to size characteristics. Journal of
Arboriculture. 22(3): 144-150

Craul, P.J. 1985. A description of urban soils and their desired characteristics. Journal of
Arboriculture. 11(11):330-339.

Cregg, B.M. and ME. Dix. 2001. Tree moisture stress and insect damage in urban areas
in relation to heat island effects. Journal of Arboriculture. 27(1):8-17

Dobbertin, M. 2005. Tree growth as indicator of tree vitality and of tree reaction to
environmental stress: a review. European Journal of Forest Research. 124: 319-333

“Emerald Ash Borer” United States Forest Service and Michigan Department of Natural
Resources. 2007. 5 July 2007. http://www.emeraldashborer.info

Galvin, M.F. 1999. A methodology for assessing and managing biodiversity in street tree
populations: a case study. Journal of Arboriculture. 25(3):]24-128

Gilman, E.F., Black, R.J., and B. Dehgan. 1998. Irrigation volume and frequency and tree
size affect establishment rate. Journal of Arboriculture. 24(1): 1-9

Ip, D.W. 1996. Community tree planting: Early survival and carbon sequestering
potential. Journal of Arboriculture. 22(5): 222-228

Jim, CY. 1998. Urban soil characteristics and limitations for landscape planting in Hong
Kong. Landscape and Urban Planning. 40(4):235-249

Kramer, P.J. 1987. The role of water stress in tree growth. Journal of
Arboriculture.13(2): 33-38

Kulman, HM. 1971. Effects of insect defoliation on growth and mortality of trees.
Annual Review of Entomology. 16: 289-324

Lauderdale, D.M., Gillman, C.H., Eakes, D.J., Keever, G.J., and Chappelka, AH. 1995.
Tree transplant size inﬂuences post-transplant growth, gas exchange, and leaf water
potential of ‘October Glory’ red maple. Journal of Environmental Horticulture.
13(4):178-181

77

Litzow, M., and Pellett, H. 1982. Establishment rates for different bareroot grades of
trees. Journal of Arboriculture. 8(10):264-266

Moser, EB, and A.M. Saxon. 1990. Repeated measures analysis of variance:
Application to tree research. Canadian Journal of Forestry Research 20:524-535.

Nowak, D.J., Crane, D.E., Walton, J.T., Twardus, DB, and J .F. Dwyer. 2002.
Understanding and quantifying urban forest structure, functions, and values. 5th
Canadian Urban Forest Conference. Region of York, Ontario. 7-9 October, 2002.

Nowak, D.J., Kuroda, M., and DE. Crane. 2004. Tree mortality rates and tree population
projections in Baltimore, Maryland, USA. Urban Forestry and Urban Greening. 2: 139-
147

Nowak, D.J., McBride, J .R., and R.A.S. Beatty. 1990. Newly planted street tree growth
and mortality. Journal of Arboriculture. 16(5): 124-129

Patterson, J .C., Murray, J .J ., and J .R. Short. 1980. The impact of urban soils on
vegetation. P. 33—56 In METRIA 3: Proceedings ﬁ'om the Metropolitan Tree
Improvement Alliance, 3rd Rutgers, New Jersey. 18-20 June 1980.

Poland, T.M., and D.G. McCullough. 2006. Emerald ash borer: Invasion of the urban
forest and the threat to North America’s ash resource. Journal of Forestry. 104(3): 1 1 8-
127

Roberts, BR. 1977. The response of urban trees to abiotic stress. Journal of
Arboriculture. 3 :75-78

Rose, AH. 1958. The effect of defoliation on foliage productionand radial growth of
quaking aspen. Forest Science. 4 (4): 335-348

Sklar, F. and R.G. Ames. 1985. Staying alive: street tree survival in the inner-city.
Journal of Urban Affairs. 7(1): 55-66

Struve, D.K., Burchﬁeld, L., and C. Maupin. 2000. Survival and growth of transplanted
large- and small-caliper red oaks. Journal of Arboriculture 26(3): 162-169

Struve, D.K., and R.J., Joly. 1992. Transplanted red oak seedlings mediate transplant
shock by reducing leaf surface area and altering carbon allocation. Canadian J ournal of

Forestry. 22 (10): 1441-1448

Watson, G.W. 1985. Tree size affects root regeneration and top growth after
transplanting. Journal of Arboriculturel l(2):37-40.

78

Watson, G.W. and EB. Himelick. 1982. Root distribution of nursery trees and its
relationship to transplanting success. Journal of Arboriculture. 8(9): 225-229

Watson, G.W., Himelick, EB, and ET. Smiley. 1986. Twig growth of eight species of
shade trees following transplanting. Journal of Arboriculture. 12(10):241-245

Watson, G.W., and G. Kupkowski. 1991. Effects of a deep layer of mulch on the soil
environment and tree root growth. Journal of Arboriculture. 17(9): 242-245

Watson, T.W. 2005. Inﬂuence of tree size on transplant establishment and growth.
HortTechnology. 15(1): 118-122

Wright, H., Nicols, D., and C. Embree. 2006. Evaluating the accountability of trunk size
and canOpy volume models for determining apple tree production potential across diverse
management regimes. Acta Horticulturae 707:

Zisa, R. P., Halverson, H. G. and BB. Stout. 1980. Establishment and Early Growth of
Conifers on Compact Soils in Urban Areas. US. Department of Agriculture Forest
Service, Northeastern Experimental Station Research Paper NE-451, Bromall, PA.

79

CHAPTER TWO

INFLUENCE OF INITIAL STOCK SIZE AND EXISTING SOIL
CONDITIONS ON GAS EXCHANGE AND PRE-DAWN MOISTURE
POTENTIAL OF TREES IN THE URBAN ENVIRONMENT

Prepared for Submission to Arboriculture and Urban Forestry

80

INFLUENCE OF INITIAL STOCK SIZE AND EXISTING SOIL
CONDITIONS ON GAS EXCHANGE AND PRE-DAWN MOISTURE
POTENTIAL OF TREES IN THE URBAN ENVIRONMENT

Additional key words: Acer xfreemanii ‘Autumn Blaze’, Platanus x acerfolia
‘Bloodgood’, Quercus bicolor, rainfall deﬁcit, stomatal conductance, transpiration, and
urban soils.

Abstract

In a companion study the inﬂuence of initial stock size on the growth and canopy
development of three tree species was evaluated in four Michigan communities. Results
from the ﬁrst year after planting suggest that smaller trees established at a quicker rate
than larger trees. This study was conducted to evaluate the potential inﬂuence of initial
stock size on gas exchange and pro-dawn moisture potential of recently planted oaks,
London plane trees, and maples. Initial stock size had no effect on the net photosynthesis
and only inﬂuenced stomatal conductance and transpiration of oaks on one of three dates
of collection. However, difference in site conditions affected gas exhancge and pre-dawn
moisture potential for all species throughout 2007 (p-values <0.0001). In addition, a
seasonal trend of increasing water deﬁcit was observed at the Lansing locations, with
mean pre-dawn moisture potentials as low as -1.92 MPa (-l9.21 bars) for 6.1 cm (2.5 in)
oaks. Results indicate that differences between trees sizes and tree growth and canopy

development during the ﬁrst two-years did not signiﬁcantly inﬂuence gas exchange.

81

Introduction

Sub-optimal growth conditions (Berrang, 1985; Oke et al., 1989; and Iles, 2003),
high mortality, and limited life spans of urban trees (Foster and Blaine, 1978) all pose a
threat to the continued health of the urban forest. Trees in the urban environment are
subjected to additional stresses when compared to trees grown in natural forest
ecosystems, which limit their grth and development potential (Roberts, 1977;
Kozlowski, 1985; Lauderdale et al., 1995; and Close et al., 1996). In addition to similar
abiotic and biotic pressures present in their native environment, stress in the urban
landscape increases precipitously with human development (Bassuk and Whitlow, 1986).

A multitude of soil (Craul, 1985; Jim, 1998; and DeKimpe et al., 2000)
atmospheric (Whitlow and Bassuk, 1988; Cregg and Dix, 2001), and environmental
(Kozlowski, 1987 and Oke et al., 1989) causes have been correlated with limited plant
growth in the urban environment (Roberts, 1977; Clark and Kjelgren, 1990; Whitlow et
al., 1992; and Close, 1996). High soil bulk density and degraded soil structure, as a result
of compaction, limit soil water availability for urban trees (Jim, 1998 and DeKimpe et al.,
2000). In addition to reduced inﬁltration from soil compaction, atmospheric drought can
result in decreased plant water potential (Kozlowski, 1987 and Whitlow et al., 1992) and
subsequently suppressed growth. Atmospheric deﬁcits also increase transpiration water
loss, reduce the rate of water absorption by the root system, and decreasing net
photosynthesis.

Previous research evaluating the water relations of urban trees has focused on

comparing trees uniform in age (Whitlow et al., 1992) and equivalent in size (Kjelgren

82

and Clark, 1993 and Cregg and Dix, 2001). These studies suggest that water stress in the
urban environment is highly variable and that trees grown in these conditions are
subjected to additional stress, when compared to trees grown in a park or forested
environment. In addition, Lauderdale et al. (1995) reported an inverse relationship
between initial stock size and tree physiology. Smaller Acer rubrum ‘October Glory’, 3.8
cm (1.5 in), trees had higher net photosynthesis, transpiration, leaf conductance, and
water use efﬁciency than larger caliper 7.6 cm (3 in) trees during the ﬁrst two years
following planting.

Water composes the majority of the fresh weight of trees, is essential for proper
physiological ﬁmction, and acts as a solvent for gas and mineral exchange for the
maintenance of turgor. Kramer (1987) attributed the role of water stress in tree growth to
a water imbalance between deposits from irrigation and rainfall and withdrawals caused
by soil evaporation and transpiration ﬁ'om the canopy. The balance between water
deposits and withdrawals is responsible for the delayed growth. Furthermore, the
alterations in transpiration during periods of low water potentials are species dependent
(Kozlowski and Davies, 1975). Therefore, it is necessary to evaluate several species to
validate the effect of water stress for a given ecosystem. Trees experiencing water stress
increases their susceptible to pest infestation (Cregg and Dix, 2001), decreased shoot
growth (Close et al., 1996), and reduces photosynthetic production (Lauderdale et al.,
1995)

Indicators of water stress include an overall reduction of tree size, trunk growth,
and individual leaf area. Over 30 years ago, Kozlowski and Davies (1975) postulated

that stomatal closure is the primary factor reducing transpiration while experiencing

83

water stress and suggest that rapid stomatal closure following exposure to increased light
intensity minimizes water loss. Prolonged water stress, referred to as drought stress, has
varying effects on plant growth and development. The primary effects are the inhibition
of photosynthesis, the loss of turgor pressure, and reduction of metabolism of
carbohydrates and nitrogen. While secondary effects include a reduction in cell size, and
increased stomatal closure.

Pre-dawn plant moisture potential has also been directly correlated to differences
in soil moisture content (Kozlowski, 1982 and Whitlow et al., 1992). A three year study
of street trees in New York City suggested that seasonal changes in pre-dawn plant
moisture content was directly attributed to similar changes in soil moisture content, while
trends of midday plant moisture potential were a function of atmospheric demand. The
results of the study further indicated that cumulative water deﬁcits are prevalent in the
Northeastern United States.

This study aims to quantify the inﬂuence of initial stock size on tree physiology in
the urban environment. Soil structural, chemical, and textural composition was
correlated with net photosynthesis, stomatal condUCtance, and transpiration will provide
insight into previously reported conclusions (Ross, 2008). The objectives of this study
are to 1) test the hypothesis that smaller trees establish at a quicker rate than larger trees,
2) determine if there is a relationship between initial stock size and net photosynthesis,
stomatal conductance, and transpiration, 3) quantify the inﬂuence of stock size on pre-
dawn moisture stress during the establishment of urban trees, and 4) evaluate potential

correlations of physiological responses to differences in soil and environmental

84

conditions. Results ﬁom this study will be used to determine if growth response of trees
in the urban environment are a function of gas exchange and pre-dawn moisture potential.
Materials and Methods
Experimental Design

Research plots in four communities within the emerald ash borer quarantine,
Detroit, Ann Arbor, Lansing, and Rochester Hills, were established in April of 2006.
Trees were monitored during the 2006 growing season to quantify the inﬂuence of initial
stock size on canopy growth and development. The three species, Acer xfreemanii
‘Autumn Blaze’, Quercus bicolor, and Platanus x acerﬂoia ‘Bloodgood’, planted at the
research plots represent potential replacements for ash (F raxinus 8p). 93 oak trees, 100
maples, and 99 plane trees broke bud in 2007 and were utilized in this study. The size
classiﬁcation of stock sizes selected for evaluation (Ross, 2008) : 3” caliper B&B (balled
and burlapped), 2 V2” caliper B&B, 2” caliper B&B, 1 3%” caliper B&B; and l 3/4” caliper
bare-root. Soil conditions for each of the four locations were analyzed in October of
2006 and differences were discussed by Ross (2008).

A Michigan State University team coordinated and installed 300 trees using
standard professional practice. Prior to installation, all trees were lightly pruned to
remove all dead and potentially conﬂicting branches. The bare-root trees were pruned
heavier than the balled-and-burlapped trees. In Ann Arbor, a PrenticeTM crane was used
to excavate the soil from each planting pit, a BobcatTM skid-steer dug the holes for all of
the planting pits in Lansing, and an auger was used in Rochester Hills. All planting pits
were ﬁnished by hand digging after initial excavation by the MSU team at all locations.

All planting pits in Detroit were manually excavated and inert material such as bricks and

85

concrete were removed ﬁ'om the planting pit. Following installation, all trees were
mulched with a 7.6 cm (3 in) layer of municipal woodchips, top-dressed with a 1/2 cup of
10-20-20 granular fertilizer (LESCO), and well watered.

Subsequent maintenance was conducted by the MSU research team. Bi-weekly
weeding and irrigation of 56.8L (15 US gal) was applied during the 2006 growing season
at all locations. All dead and broken branches were removed throughout the season and
trees were inspected for damage from insects and vandalism. At the end of the ﬁrst
growing season all mulch rings were top-dressed with an additional 2.5 to 5 cm (1 to 2 in)
to compensate for decomposition. In 2007, the trees were not irrigated in accordance
with the cultural practices of each of the four communities.

Photosynthesis, T ranspiration, and Stomatal Conductance.

During the 2007 growing season photosynthesis (Pn), transpiration (E), and
stomatal conductance (6,) were analyzed using a portable CIRAS-Z photosynthesis
system with a PLC6 circular leaf cuvette measuring 2.5cm2 of leaf area (PP Systems,
Amsbury, Massachusetts). Gas exchange was measured at the same time as soil
volumetric water content at all locations. Measurements were taken from a single leaf
within the mid-canopy for each of the trees in June, July, and August of the 2007 growing
season at each of the research plots. Gas exchange was measured at each of the sites
independently during mid-day (1000-1400 h).

Volumetric Soil Moisture Content

Monthly measurements of volumetric soil moisture content at 15 cm (6 in) were

monitored using a Trase Systems 1 model 6050Xl (Soil Moisture Equipment

Corporation, Santa Barbara, California) time domain reﬂectometer, with a sampling error

86

of :I:Z%. Due to compacted soil conditions at all locations, an alignment block and
slamrner were required for the proper insertion of two 15 cm stainless-steel waveguides.
Volumetric moisture content of the root-ball was collected 15 cm from the trunk, backﬁll
measurements were taken at the midpoint of the edge of the planting pit and the rootball,
and undisturbed soil was monitored 30 cm from the edge of the planting pit.
Pre-Dawn Moisture Potential

Pre-dawn moisture potentials (w) were collected from the Lansing sites during the
2007 growing season, on July 5, July 24, August 15 — 17. Sub-samples of two fully
expanded leaves from the middle-canopy wgrf: analyzed from each of the 75 trees on July
5‘h and 24th. In order to complete all measurements between 0200 and 0500b, a sample
size of two leaves were collected. After initial analysis of the July data, the sample size
was expanded to ﬁve leaves samples in an attempt to separate the means of each size
classes by decreasing sampling variability. The increase in samples size prevented
collection in one session and pre-dawn moisture content was monitored species
independently over a three day period from August 15-17. Samples were analyzed in the
ﬁeld between 0200 and 0500 h using a portable pressure chamber model B (Soil Moisture
Equipment Corporation, Santa Barbara, California) immediately after leaves were
removed from the tree as suggested by Blum et al. (1973).
Analysis

Seasonal trends of gas exchange rates, pre-dawn moisture potentials, and
volumetric soil content was analyzed using the PROC MDIED function in a repeated
measure design using SAS version 9.1.3 (SAS Institute Inc., Cary, N.C.). The inﬂuence

of initial size, species, location, time of year, and all interactions were reported with a .05

87

signiﬁcance level (0:0.05). Signiﬁcant differences of means were separated using
Tukey’s adjustment (SAS). Differences in soil characteristics between site locations and
rainfall deﬁcit were acquired using PROC MIXED without a repeated measure design.

The relationship of soil chemical, structural, and textural characteristics and tree
physiology was analyzed using the PROC CORR function (SAS). Correlations between
bulk density, cation exchange capacity, % sand, volumetric water content, and pH with
monthly transpiration, photosynthesis, stomatal conductance were reported in a Pearson’s
correlation matrix.
Results and Discussion

Data analyzed from 300 trees planted in four urban Michigan communities (Ross,
2008) quantiﬁed the inﬂuence of initial trees size on tree growth and canopy
development. Results from this companion study suggested that one cause for the
difference in tree growth and canopy development could be the result of alterations in
physiological function. This study was conducted to better examine if initial tree size had
an inﬂuence on gas exchange and pre-dawn moisture potential.
Photosynthesis, Stomatal Conductance, and T ranspiration

In our study, month, location, and interactions of month and location affected the
gas exchange of all three species. Species independent analysis, indicates that size is not
a signiﬁcant factor in determining the net photosynthesis of maples (p-value 0.6218),
oaks (p-value 0.1813), and planes (p-value .1757). Furthermore, when data is analyzed
for each species for each month only the transpiration and stomatal conductance of the
oak trees are signiﬁcantly inﬂuenced by initial tree size.(p-value 0.0008). In July the

only signiﬁcant difference of transpiration was between the 4.4 cm (1.75 in) bare-root

88

and 6.5 cm (2.5 in) oaks with means of 2.8 and 1.73, respectively. Stomatal conductance
of oaks in July also was signiﬁcantly inﬂuenced by tree size (p-value .0312).

In general, the relative magnitude of the inﬂuence of location diminished over
time (Table 2-1). Stomatal conductance and transpiration of London plane trees and
stomatal conductance of Autumn Blaze maples were no longer affected by location in
August. Oak trees planted in Rochester Hills had the lowest rate of photosynthesis when
compared to all other locations perhaps as a result of the high bulk density, pH, and
concentration of calcium (Ross, 2008). In addition photosynthesis, stomatal conductance,
and transpiration of all three species was lowest in Detroit in June. A greater increase in
photosynthesis in subsequent months in Detroit coupled with a reduction in Lansing from
June to July affected the differences in site locations. The photosynthetic rate of plane
trees was no longer inﬂuenced by site location in August.

An inverse relationship between initial tree size of Acer rubrum ‘October Glory’
and gas exchange was suggested by Lauderdale et a1. (1995). Net photosynthesis,
transpiration, and stomatal conductance were greater in smaller caliper trees throughout
the ﬁrst two years of establishment. In their study, mean photosynthesis in August of the
smaller caliper trees was 9.0 and 12.8 pmolm’zs'l while the larger caliper trees had net
photosynthesis of 5.1 and 8.7 umolm'zs'l during the ﬁrst two years of establishment. It
was suggested that the difference in gas exchange between 3.8 cm (1.5 in) and 7.6 cm (3
in) sized red maples was the result of smaller trees having a faster rate of establishment

than the larger caliper trees (Lauderdale et al. 1995).

89

Inﬂuence of Urban Soils on Tree Physiology

Correlations between soil conditions and the growth and canopy development of
the trees in this study suggest that soil conditions were inﬂuential in determining growth
and canopy development during the 2007 growing season (Ross, 2008). There were
signiﬁcant correlations of gas exchange with differences in soil conditions (Table 2-2).
Results ﬁ‘om the correlation analysis indicate that soil conditions were more inﬂuential in
determining the physiological functions of the trees in June and August. In addition,
there was not a signiﬁcant correlation between average volumetric soil moisture content
or soil texture and gas exchange in July. Furthermore there was a strong correlation
between stomatal conductance and soil conditions. This is a unique phenomenon that
may the result of different vapor pressures at each of the locations which were
responsible for the differences in stomatal conductance. Cregg and Dix (2001) and
Bassuk and Whitlow (1996) both suggested that the water stress is not solely dependent
upon soil moisture content.

The most abundant and strongest correlations were observed for the month of
June when transpiration and photosynthesis were correlated with chemical, textural, and
structural soil parameters except for bulk density (Table 2-2). The chemical component
of soils which had the least correlation was magnesium which is probably the result of
average concentrations at all locations. Soil moisture had the strongest correlation with
stomatal conductance and transpiration in July when the Lansing and Detroit locations
had the lowest volumetric water content (data not shown).

Two of the more interesting signiﬁcant correlations presented are that of the

relationships between pH and calcium with tree physiology. Negative correlation

9O

coefﬁcients suggest that as soil pH and calcium concentration increase, the physiological
function decreases. The strongest correlation of -.46, described the inverse relationship
between soil pH (p-value <0.0001) and the stomatal conductance (p-value >0.0001) in
June. Transpiration in June had the strongest negative correlation with calcium
concentrate with a coefﬁcient of -.52 (Table 2-2). Therefore transpiration decreased in
soils with a higher concentration of calcium.
Pre-dawn Moisture Content

Pre-dawn moisture potential has a negative effect on net photosynthesis and
stomatal conductance (Ritchie and Hinckley, 1975), however pre-dawn moisture
potential and gas exchange measurements were not taken on the same day. We were un
able to monitor pre-dawn moisture stress at all locations. However site location had a
signiﬁcant effect on volumetric water content in June, July, and August of 2007 (p-values
of <0.0001 for all months) and rainfall deﬁcits were wide-spread during 2007. In
addition to monitoring pre-dawn moisture stress, quantifying the vapor pressure deﬁcit
(Bassuk and Whitlow, 1986 and Cregg and Dix, 2001) and the soil/ root water potential
(Reich and Hinckley, 1989) should be considered. Reich and Hinckley (1989) concluded
pre—dawn moisture potential collected from leaves was not a signiﬁcant factor in
determining differences in the gas exchange of blackjack oak (Quercus marilandica
Muenchh.) and northern red oak (Quercus rubra Lam.).

Pre-dawn moisture potentials measured in June and July indicated species
differences (p-value <0.0001); however size was only an inﬂuential factor for maples in
July (p-value 0.0449). Although not statistically signiﬁcant, data from June and July

suggested that tree size may inﬂuence the pre-dawn moisture potential of maples and

91

planes. Analysis of data separated by species and time ﬁirther support this relationship.
We postulated that the nmnerical differences exhibited in June and July could be ﬁrrther
investigated by increasing the sample size from two to ﬁve leaves and the f-values of the
effect of tree size on pre-dawn moisture potential increased as the season progressed
(Table 2-3). Increasing the sample size prevented the collections of data ﬁom all 75 trees
in the Lansing location during one session between 0200 and 0500b. Our treatment of
interest was size and preliminary analysis of data had already determined that each of the
three species had different levels of pre-dawn moisture potential.

The increased inﬂuence of size on pre-dawn moisture stress suggests that as the
stress of trees increased from a seasonal deﬁcit. Unlike the 3-year study of street trees in
New York which only had a difference of -l .0 mPa (Whitlow et al., 1992), pre-dawn
moisture potentials became more negative in July and August. This increasing pressure
potential indicates a seasonal deﬁcit in water availability. Means of each size, were
separated by species, and are presented in Table 2-4. In June, there was no signiﬁcant
inﬂuence of initial size on pre-dawn moisture potential and in July, size was only an
inﬂuential factor in determining pre-dawn moisture potential of maples. Despite the
signiﬁcance of tree size in determining pre-dawn moisture potential of maples in July (p-
value 0.0449), means were not able to be separated by size classiﬁcation.

In August, sample size was increased from the original measurement of two
leaves from each tree collected in a single night to ﬁve leaves per tree over the course of
three nights. Increasing the sample size pregsnted data collection and measurement of all
trees between 0200 and 0500 h, due to the distance between sites and equipment

availability. Maples were collected on August 15, planes on August 16, and oaks on

92

August 17, which prevented statistically analyze species differences, however the
inﬂuence of size of pre-dawn moisture potential for maples and oaks were signiﬁcant (p-
values of 0.0006 and 50.0001).

The 7.6 cm (3 in) maples had the greatest, most negative, mean pressure potential
of -8.83 which was signiﬁcantly greater than that of the 5.1 cm (2 in) and 6.4 cm (2.5 in)
size which had pressure potentials of -7.05 and -6.86 respectively (Figure 2-1). The 6.4
cm (2.5 in) oaks had the greatest, most negative, pre-dawn moisture potential -1 9.21 bars.
Pressure potentials of the 4.4 cm (1.75 in) bare-root, 4.4 cm (1.75 in) balled-and-balled,
and 5.1 cm (2 in) were -10.34, -11.48, -15.88 bars. Except for the 7.6 cm (3 in) size (-
11.1 bars), as the initial tree size of oaks increased from 4.4 cm (1.75 in) to 6.4 cm (2.5
. in), the pressure potential increase suggesting that larger trees had a greater demand for
water than smaller trees (Figure 2-1). During 2006, two of the three 7.6 cm ( 3 in) had
died and been removed ﬁom the study. The loss of these trees may have been the reason
why the 7.6 cm (3 in) oaks did not have a greater mean pressure potential than the other
sizes.

Adequate sample size may not be the only contributing factor in the separation of
means in August. A higher rainfall deﬁcit in Lansing in August could have increased the
degree of stress of trees during the establishment process further exacerbating the
differences in pressure potentials. Between data collection on July 24 and August 15
there was a cumulative rainfall deﬁcit of 62 mm.

Conclusions
The results from this study suggest that the inﬂuence of stock size on canopy

growth and development are not inﬂuenced by the physiological parameters we

93

monitored. The inﬂuence of initial stock size on tree growth and development were more
signiﬁcant than the inﬂuence of initial stock size on gas exchange (Ross, 2008). In
general, shoot elongation, trunk growth, leaf area, and canopy development were found to
be greater for smaller caliper trees (Ross, 2008). Our original postulation that the
increased growth was caused by increased photosynthetic production was not supported
by data collected during the second year of establishment.

There is a strong relationship between urban tree gas exchange and site
conditions. During the ﬁrst two years of establishment, differences in photosynthesis,
stomatal conductance, and transpiration were all signiﬁcantly inﬂuenced by urban soil
conditions. The relationships between soil chemical, structural, and textural
characteristics and tree physiology were most evident in June and August. Further
research is needed to quantify the relationship between urban soils and tree physiology,
although the homogeneity of these soils and their exogenous sources remain a challenge.

The results from the analysis of pre-dawn potentials indicate that the lack of
irrigation and below average precipitation in June and July in 2007 for all sites resulted in
a seasonal water deﬁcit. The seasonal water deﬁcit was measured by increasing pressure
potentials during July and August. Furthermore, when evaluating the inﬂuence of tree
size on pre-dawn moisture potential an increase in sample size from two to ﬁve leaves
proved to be an effective. The urban environment presents a unique challenge to forestry
research and the complexity of in situ studies requires further investigation in order to

determine if the relationships concluded from controlled research are to be applied.

94

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Pro-dawn Pressure Potenital (-bars)

-10

-15

-20

-25

 

 

 

 

l l I I I

BR 1.75 2 2.5 3

Initial Tree Size

Figure 2-1. Inﬂuence of initial tree size on pre-dawn moisture potential (-bars)
of ﬁve sizes of Quercus bicolor on 17 August 2007 in Lansing, MI

BR reprwsnts the 4.4 cm (1.75 in) size class

98

Literature Cited

Bassuk, N.L, and T. Whitlow. 1986. Urban stress is not limited to people. American
Nurseryman. 163257-61 '

Berrang, P., Karnosky, D.F., and B.J. Stanton. 1985. Environmental factors affecting tree
health in New York City. Journal of Arboriculture. 11:185-189

Blum, A., Sullivan, C.Y., and J .D. Eastin. 1973. On the pressure chamber technique for
estimating leaf water potential in sorghum. Agronomy Journal. 65: 337-338

Clark, J .R., and R. Kjelgren. 1990. Water as a limiting factor in the development of urban
trees. Journal of Arboriculture. 16(8):203-208

Close, R.E., Nguyen, P.V., and J .J . Kielbaso. 1996. Urban vs. natural sugar maple
growth: 1. Stress symptoms and phenology in relation to site characteristics. Journal of
Arboriculture. 22(3): 144-150

Craul, P.J. 1985. A description of urban soils and their desired characteristics. Journal of
Arboriculture. 11(11):330-339.

Cregg, B.M. and ME. Dix. 2001. Tree moisture stress and insect damage in urban areas
in relation to heat island effects. Journal of Arboriculture. 27(1):8-17

DeKimpe, C.R., Christian, R., and M. Jean-Louis. 2000. Soil Science. 165(1):31-4O

Foster, RS. and J. Blaine. 1978. Urban tree survival: trees in the sidewalk. Journal of
Arboriculture. 4(1): 14-17

Iles, J .K. 2003. The science and practice of stress reduction in managed landscapes. Acta
Horticulturae. (618):1 17-124

Jim, CY. 1998. Urban soil characteristics and limitations for landscape planting in Hong
Kong. Landscape and Urban Planning. 40(4):235-249

Kjelgren, R.K., and J .R. Clark. 1993. Water relations of sweetgum in an urban canyon
and park. Journal of Arboriculture. 19(5): 266-270

Kozlowski, T.T. 1985. Tree growth in response to environmental stresses. Journal of
Arboriculture. 1 1(4): 97-1 11

Kozlowski, T.T. 1987. Soil moisture and absorption of water by tree roots. Journal of
Arboriculture 13(2): 39-46

Lauderdale, D.M., Gillman, C.H., Bakes, D.J., Keever, G.J., and Chappelka, AH. 1995.
Tree transplant size inﬂuences post-transplant growth, gas exchange, and leaf water

99

potential of ‘October Glory’ red maple. Journal of Environmental Horticulture.
13(4):]78-181

Oke, T.R., Crowther, J .M., McNaughton, K.G., Monteith, J .L., and B. Gardiner. 1989.
The micrometeorology of the urban forest. Biological Sciences. 324 (1223): 335-349

Reich, RB, and TM. Hinckley. 1989. Inﬂuence of pre-dawn water potential and soil-to-
leaf hydraulic conductance on maximum daily leaf diffusive conductance in two oak
species. Functional Ecology. 3 (6): 719-726

Ritchie, GA, and TM. Hinckley. 1975. The pressure chamber as an instrument of
ecological research. Advances in Ecological Research. 9: 165-254

Roberts, BR. 1977. The response of urban trees to abiotic stress. Journal of
Arboriculture. 3:75-78

Ross, M.R.2008. Inﬂuence of stock size on canopy grth and development Master’s
Thesis. Michigan State Univeristy. 123 p.

Vrecenak, A.J., Vodak, M.C., and LE. Fleming. 1989. The inﬂuences of site factors on
growth of urban trees. Journal of Arboriculture. 15(9): 206-209

Whitlow, T., Bassuk, N.L. and D. Reichert. 1992. A 3-year study of water relations of
urban street trees. Journal of Applied Ecology 29:436—450

lOO

APPENDIX

101

Table A-1. F-values of cumulative survival percentages of Acer xfreemanii
'Autumn Blaze', Quercus bicolor, and Platanus x acerfolia 'Bloodgood'
during ﬁrst two years of establishment in four Michigan Communities

 

 

 

Acer xfreemanii Quercus bicolor Platanus x acerfolia
'Autumn Blaze' 'Bloodgood'

DE E: .11: 2E E; E IE E &
.Eﬁeﬂ value value value value KM ME
S 4 0.30 NS 4 0.39 NS 4 2.24 NS
L 4 1.16 NS 4 0.93 NS 3 2.98 *
Y 2 0.53 NS 2 5.52 * 2 1.92 NS
S x L 16 0.51 NS 16 0.80 NS 12 1.45 NS
S x Y 8 0.40 NS 8 0.94 NS 8 0.93 NS
L x Y 8 0.93 NS 8 0.54 NS 6 1.63 NS
S x L x 32 0.70 NS 32 0.71 NS 24 0.82 NS
Y

 

Size (S) refers to intial stock size, location (L) represents location of research
plot, and year (Y) refers to data collected in October 2006, October 2007, and
June 2008

Table A-2. F-values of the visual assessment rating of Acer xﬁeemanii
'Autumn Blaze', Quercus bicolor, and Platanus x acerfolia 'Bloodgood'
during ﬁrst two years of establishment in four Michigan Communities

 

 

 

 

 

M Acer xfreemanii Quercus Platanus x acerfolia
‘Autumn Blaze’ bicolor ‘Bloodgood’

S 0.70 NS 15.09 *** 12.58 ***

L 13.41 *** 8.32 *** 42.11 ***

Y 0.31 NS 4.60 * 0.24 NS

S x L 1.32 NS 1.86 * 3.23 **

S x Y 0.31 NS 0.26 NS 1.09 NS

L x Y 1.10 NS 4.99 ** 1.97 NS

S x L xY 0.51 NS 1.43 NS 0.81 NS

 

Size (S) refers to initial stock size, location (L) refers to the location of
research plot, and year (Y) refers to data collected in June of 2007 and 2008
*,**,*** p S 0.05, 0.01.0.0001 respectively

102

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Table A-8. Pearson correlation coefﬁcients of visual assessment
ratings in relation to relative growth rate (RGR), light
interception (LI), leaf area (LA), branch growth (BG), and
cumulative survival percentage (SURV) from April 2006 to
June 2008

Visual Assessment Rating

2007 2008

RGRl 0.15 * 0.1 1 NS
RGR2 0.41 *** 0.37 ***
LUUN 0.52 *** 0.41 ***
LUUL 0.41 *** 0.41 ***
LIAUG 0.32 *** 0.31 ***
LA06 -0.01 NS 0.03 NS
LA07 -0. 12 * 0.02 NS
LA08 0.14 * 0.1 1 NS
BG06 0.13 * 0.08 NS
BG07 0.32 *** 0.26 ***
SURV06 0.37 ***

SURV07 0.36 *** .

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