PRE-PLANT STORAGE AND HANDLING OF DIFFICULT TO TRANSPLANT ASH
ALTERNATIVES
By
Dana Suzanne Ellison

A THESIS
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of
MASTER OF SCIENCE
Horticulture
2012

ABSTRACT
PRE-PLANT STORAGE AND HANDLING OF DIFFICULT TO TRANSPLANT ASH
ALTERNATIVES
By
Dana Suzanne Ellison
The loss of ash (Fraxinus spp.) trees in the midwestern United States due to emerald
ash borer has emphasized the need for more diversity in urban and community forests.
However, nursery growers report that many Fraxinus spp. alternatives are difficult to
transplant. Understanding the physiological reasons why one tree species has superior
transplantability over another is an important factor in increasing production of Fraxinus
spp. replacements. In this study, we examined five difficult to transplant ash
alternatives; Celtis occidentalis, Quercus bicolor, Quercus ellipsoidalis, Quercus rubra,
Taxodium distichum, and Fraxinus americana. To mimic nursery grower practices,
trees were assigned at random to one of four treatments: 1) control, 2) heeled-in, 3)
cold storage, or 4) sweating. After treatment, trees were assigned at random to one of
three evaluations: root growth potential (RGP) test, container planting or field planting.
Root growth potential was very low for Quercus spp. trees and varied by treatment for
C. occidentalis. Taxodium distichum trees had a relatively high root growth potential in
all treatments. Stem water potential measured immediately before and after pre-plant
treatments suggest that Quercus spp. trees and T. distichum trees were able to
rehydrate during sweating while water stress levels in C. occidentalis trees remained
high. The results suggest that poor transplanting success reported for Quercus spp.
trees may be related to low root growth potential, whereas poor success of C.
occidentalis trees may be due to shoot desiccation during storage and handling.

ACKNOWLEDGEMENT

I wish to show my gratitude to Dr. Bert Cregg for giving me the opportunity to be a part
of the project and for the support and guidance he has given me along the way. I would
also like to thank Dr. Bob Schutzki and Dr. Pascal Nzokou for sitting on my committee.
I wish to thank my dad for his tremendous contributions and support both morally and
financially towards the completion of my master’s degree. I am also grateful to my
siblings for the encouragement and optimism during this great journey. I also show my
appreciation to my friends and all who contributed in one way or the other in the course
of the project.

iii

TABLE OF CONTENTS

LIST OF TABLES ............................................................................................................ v
LIST OF FIGURES .......................................................................................................... vi
INTRODUCTION ............................................................................................................. 1
CHAPTER ONE
LITERATURE REVIEW
Importance of the problem .................................................................................... 4
Renewed interest in diversity ................................................................................ 4
Bareroot production cycle ..................................................................................... 5
Potential causes of the problem ........................................................................... 7
Approach to dealing with transplant stress ......................................................... 10
Appendix 1.......................................................................................................... 14
Literature Cited ................................................................................................... 16

CHAPTER TWO
PRE-PLANT STORAGE AND HANDLING OF DIFFICULT TO TRANSPLANT ASH
ALTERNATIVES
Abstract .............................................................................................................. 21
Introduction ......................................................................................................... 22
Materials and Methods ....................................................................................... 26
Results ............................................................................................................... 32
Discussion .......................................................................................................... 37
Conclusion .......................................................................................................... 44
Appendix 2.......................................................................................................... 45
Literature Cited ................................................................................................... 71

iv

LIST OF TABLES

APPENDIX 2
Table A2.1. Overview of plant material, pre-plant treatments and evaluations of 20102011 pre-plant storage and handling tests .................................................................... 46
Table A2.2. Growth and physiology measurement dates 2010 ..................................... 47
Table A2.3. Growth and physiology measurement dates 2011 ..................................... 48
Table A2.4. Schedule of treatments and evaluations for pre-plant handling trial 2010 .. 49
Table A2.5. Schedule of treatments and evaluation tests for pre-plant handling trial
2011 .............................................................................................................................. 50
Table A2.6. Mean predawn and midday water potential (Ψw) of container-grown
bareroot tree liners subjected to four pre-plant treatments. July 23, 2010.................... 51
Table A2.7. Mean predawn and midday water potential (Ψw) of field-grown bareroot tree
liners subjected to four pre-plant treatments. July 23, 2010 ......................................... 52
Table A2.8. Mean chlorophyll fluorescence of container-grown bareroot tree liners
subjected to four pre-plant treatments for two dates; June 29, 2010 and September 1,
2010 .............................................................................................................................. 53
Table A2.9. Mean chlorophyll fluorescence of field-grown bareroot tree liners subjected
to four pre-plant treatments for two dates; June 29, 2010 and September 1, 2010 ....... 54
Table A2.10. Mean predawn and midday water potential (Ψw) of container-grown
bareroot tree liners subjected to four pre-plant treatments. July 21, 2011.................... 55
Table A2.11. Mean predawn and midday water potential (Ψw) of field-grown bareroot
tree liners subjected to four pre-plant treatments. July 21, 2011 .................................. 56
Table A2.12. Mean chlorophyll fluorescence of container-grown bareroot tree liners
subjected to four pre-plant treatments. June 16, 2011. ................................................. 57
Table A2.13. Mean chlorophyll fluorescence of field-grown bareroot tree liners subjected
to four pre-plant treatments for two dates; June 16, 2011 and August 24, 2011 ........... 58

v

LIST OF FIGURES

APPENDIX 1
Figure A1.1 Simulation of the emerald ash borer spread in counties from March 2010 to
March 2020 (base case). The maps represent the rounded average of 200 stochastic
simulations (Kovacs et al., 2011) .................................................................................. 15

APPENDIX 2
Figure A2.1. Mean initial water potential of bareroot tree liners subjected to four preplant treatments prior to planting ................................................................................... 59
Figure A2.2. Mean root number of root growth potential-grown bareroot tree liners
subjected to four pre-plant treatments ........................................................................... 60
Figure A2.3. Mean growth/dieback of container-grown bareroot tree liners subjected to
four pre-plant treatments ............................................................................................... 61
Figure A2.4. Mean growth/dieback of field-grown bareroot tree liners subjected to four
pre-plant treatments ...................................................................................................... 62
Figure A2.5. Mean growth/dieback of root growth potential-grown bareroot tree liners
subjected to four pre-plant treatments ........................................................................... 63
Figure A2.6. Mean total non-structural carbohydrate content of roots of bareroot tree
liners collected pre- and post-harvest............................................................................ 64
Figure A2.7. Mean total non-structural carbohydrate content of shoots of bareroot tree
liners collected pre- and post-harvest............................................................................ 65
Figure A2.8. Mean water potential of bareroot tree liners prior to harvest (pre-harvest),
after harvest (post-harvest), and four pre-plant treatments prior to planting.................. 66
Figure A2.9. Mean root number of root growth potential-grown bareroot tree liners
subjected to four pre-plant treatments ........................................................................... 67
Figure A2.10. Mean growth/dieback of container-grown bareroot tree liners subjected to
four pre-plant treatments ............................................................................................... 68
Figure A2.11. Mean growth/dieback of field-grown bareroot tree liners subjected to four
pre-plant treatments ...................................................................................................... 69

vi

Figure A2.12. Mean growth/dieback of root growth potential-grown bareroot tree liners
subjected to four pre-plant treatments ........................................................................... 70

vii

INTRODUCTION
Improving our understanding of factors that contribute to poor transplanting success
of important ash alternatives will have direct impacts on landscape nurseries in
Michigan and surrounding states and on landscapers and urban foresters.
Improving the diversity of species available for urban tree planting is critical in many
areas of Michigan. In order to meet the demand to replace trees lost to emerald ash
borer, urban and community foresters must rely on currently available species, many
of which are already over-represented in these communities. Continued overreliance on a few species increases the potential for catastrophic tree losses due to
future exotic pest introductions.
The goal of this project was to improve the overall availability and success of
important ash alternative species in production nurseries to facilitate a more diverse
urban landscape.
The objectives of this study was to determine the effect of pre-plant handling on
initial survival and growth of ash alternatives and to determine the rehydration, root
growth potential and carbohydrate response of ash alternatives following pre-plant
handling. Pre-plant treatments act to overcome dormancy, promoting rapid bud
break and subsequent leaf area development. They also promote rapid resumption
of root growth resulting in greater root-soil contact and minimizing overall tree
moisture stress following transplanting. A secondary objective of this project is to
determine the utility of gravel culture as a system to evaluate tree root growth
potential.

1

The results of this study will aid urban and community foresters in their goal of
working toward a widely diverse landscape. Tree diversity in community and urban
forests can help mitigate crises that are caused by exotic pests and diseases, like
the emerald ash borer.

2

CHAPTER ONE
LITERATURE REVIEW

3

Importance of the problem
The scope and value of shade tree nurseries and hardwood forest nurseries in
the United States is preeminent. Tree production and care services were valued at
$14.55 billion in 2002, with a total output impact of $21.02 billion, and creating over
250,000 jobs (Hall et al., 2005). Also stated in the study, well landscaped homes with
suitable tree canopy have a 7 to 11 percent premium in value compared to similar
properties without such additions. In 2006, deciduous shade trees were the third
ranking category of nursery production crops with total sales of $584 million, up 14
percent from 2003 (United States Department of Agriculture, 2007). Landscape trees in
the urban community are not only important for economic advantages but for
environmental improvements. Other studies have shown the importance of other nonmonetary economic and environmental impacts, including energy savings for building
heating and cooling, reduction of atmospheric CO2, enhanced air quality, reduced runoff
from stormwater, and other aesthetic benefits (Hall et al., 2005).
Renewed interest in diversity
Tree diversity in community and urban forests can help mitigate crises that are
caused by exotic pests and diseases, like the emerald ash borer and Dutch elm
disease. These devastating losses seen in communities may have been avoided by
creating a diverse landscape to spread the risk of an exotic pest or disease from
destroying an entire community. Monoculture had been the main reason why Dutch elm
disease overwhelmed towns and cities killing a significant portion of urban forests. After
the devastation caused by the Dutch elm disease over a 40-year period, attention was
given to the dangers of planting a single species or only a few species in the landscape

4

(Bassuk, 1990). However, history seemed to repeat itself with the over abundance of
ash (Fraxinus spp.) trees planted in urban communities and the invasion of the emerald
ash borer in the early 1990s, detected in 2002. Many community forests were infected
in mid-western states, most prevalently in Michigan. There are efforts to slow the
progression of the EAB spread throughout the Midwest and beyond, by using a program
called SLAM (SLow Ash Mortality) (Collins & Mccullough, 2012). This program, a
collaborative effort between universities and government agencies, is to impede and
decrease the expansion of ash mortality by diminishing populations of the beetle in
newly-infested sites, outside of known EAB infestations (Collins & Mccullough, 2012).
Even with the efforts to slow down the spread of the EAB, Kovacs et al. (2011) project
the spread of EAB based on the current rate of spread to infest roughly 30 states by
2020 (Figure A1.1).
The reduction in the beetle population and rate of spread is important, however,
creating a diverse landscape is also important. Biological diversity is regarded as the
basis for ecological stability (Cleland, 2011), consequently creating a diverse urban
landscape is essential. Also, street trees are generally the main focus for many
community forestry programs and the resources for establishment, maintenance, and
removal of these trees consist of the majority of many urban forestry budgets (Kielbaso
et al. 1988). Diversity in community and urban forests is important so depredation of
entire communities can be prevented.
Bareroot production cycle
The journey of a bareroot landscape tree from liner production to the landscape
is a long and arduous one. The venture begins at the liner/propagation nursery where

5

the bareroot liners are lifted from the field in early to mid-winter and placed in storage.
The root system is, more often than not, compromised during harvest, handling, storage
and shipping, and root pruning before transplanting (Struve, 1996). The storage area
may be inside a barn with low light, in a refrigerated barn with low light, or outdoors in
substrate, like sawdust or woodchips (Englert et al.,1993). They remain in this storage
facility until processed for delivery. The delivery process begins by loading an order
onto a refrigerated truck. Depending on where the trees are being delivered and how
many different orders are being filled, the trees could remain in the truck for up to three
weeks. Once the trees are delivered, the nurseries will typically employ storage
techniques or treatments; heeling-in, cold storage, sweating, and misting. The
techniques or treatments include burying the roots in a mulch trench outdoors (heelingin), storing them in a shed or barn where there are low light and cool temperature
conditions (cold storage), storing them in a warm and humid greenhouse under moist
burlap (sweating), or submerging the roots in a pond or spraying the tree with water
(misting). The storage techniques or treatments will commonly last for a few weeks until
the ambient temperatures are adequate for transplanting. The wholesale nursery will
typically grow the trees on for 1 to 3 years and then sell them to retail nurseries or
landscape companies.
During the period of time that the bareroot trees are handled and stored, they can
become desiccated. The nurseries will typically employ those storage techniques or
treatments; heeling-in, cold storage, sweating, and misting, to aid in rehydration of the
roots and shoots, overcome dormancy, and initiate bud break. Different species,
however, react differently to these treatments. For example, Norway maple (Acer

6

platanoides L.) is a desiccation-tolerant species that can operate under low water status
conditions and survive, while Washington hawthorn (Crataegus phaenopyrum Med.) is a
desiccation-intolerant species that does not succeed under low water status conditions
(Murakami et al., 1990). These treatments, regardless of species, are meant to improve
the survivability of the trees after transplanting.
Potential causes of the problem
Regardless of the high probable mortality rate due to transplant shock, bareroot
whips or lightly branched bareroot liners are the most commonly used because the ease
of handling and shipping (Struve, 1996). The high mortality is generally due to the lifting
and the amount of root pruning done to the liners when harvested (Struve, 1996). The
reestablishment of the root system after transplanting is an important factor for tree
survival. A consequence of a disproportion in the shoot surface to the root surface can
result in water stress for bareroot seedlings (Baldwin & Barney, 1976). Factors affecting
root regeneration and bud break are carbohydrate status and water status in the plant.
The initiation of new roots by bareroot trees depend on the amount of carbohydrates
stored in the stem and root tissues (Webb & Lakes, 1980). There is a seasonal
carbohydrate flux in trees that affects the amount stored for reserves. Trees undergo
an autumn buildup of carbohydrates to store for overwintering and to be used for spring
establishment (Kobe, 1997). These stored carbohydrates are essential for the regrowth of roots and initiation of bud break at planting. Tree species that have episodic
shoot growth during the season will retain less reserves in the fall than tree species that
have an initial burst of shoot growth in the early growing season (Canham et al., 1999).

7

Carbohydrates are important for the trees ability to overcome stresses imposed
during the production cycle. In the most collective terms, carbohydrate reserves
seemingly play a crucial role in the reestablishment and revival of seedlings from a wide
range of agents of stress and physical damage, encompassing from herbivory to frost
heaving (Canham et al., 1999). Carbohydrate status is affected by respiration,
temperature, and duration of cold storage (Ritchie, 1982). If an insufficient amount of
carbohydrates is available the tree will be stressed upon transplanting. Davis & Jacobs
(2005) explain that root carbohydrate content may possibly forecast seedling survival
and growth when transplanted, most notably when seedlings are not photosynthesizing.
They also state that the root carbohydrate content could be an indication of the internal
reserves and could prove useful in ameliorating the survival of species that are likely to
have dieback (i.e., Quercus spp.) (Davis & Jacobs, 2005). In storage situations,
moderate temperatures and light deprivation over a continual period will accelerate the
rate at which stored carbohydrates are used and it may contribute to the reduced root
initiation and growth needed from the stored carbohydrates (McKay, 1996). A recent
study by Cabral & O’Reilly (2008) showed that warm storage before planting did not
benefit bareroot trees. Some nurseries may store the bareroot trees in an environment
which may be warmer than the storage conditions the trees previously experienced.
The study explains that trees placed in warm storage experienced delayed bud break
and shoot growth, reduced height and diameter growth, stem quality, total biomass, and
root growth. The longer the trees were stored in the warm environment the more
negative affects were observed (Cabral & O’Reilly, 2008).

8

Root growth potential (RGP) is the ability of a tree to initiate and lengthen roots
when placed into an environment favorable for root growth (Ritchie, 1985).
Characteristics to quantify root growth include number of new roots, roots greater than a
specific length, total root lengths, and regenerated roots (Struve, 1990). These
characteristics are used to predict field performance and survival. The degree of RGP
is often associated with survival and growth. Struve (1990) explains that root
morphology and the rate of root regeneration are factors in the ease of transplanting.
Coarse-rooted species (Hallgren & Tauer, 1989)regenerate new roots from adventitious
roots, while fibrous-root species regenerate roots primarily through elongation of
existing roots and subsequently from adventitious roots (Struve, 1990). Important
factors that can implement control of RGP are date of lifting and duration of cold storage
(Ritchie, 1985). Root growth potential or actual root growth are affected by
temperature, water content, carbohydrate status, storage, and handling. Root growth
potential varies seasonally, with the highest potential occurring mid-winter (Ritchie,
1985). The handling or mishandling of bareroot trees also affects the RGP when trees
are lifted and/or stored (Simpson & Ritchie, 1996).
Water status of bareroot trees is another important factor in a successful
transplant. Desiccation stress imposed at harvesting, storage, shipping, and
transplanting is thought to be one of the major causes of re-growth failure (Murakami et
al., 1990). There is a period during the dormant season when trees have the highest
desiccation tolerance. The peak time and range of desiccation tolerance differs
between species. Many of the trees have their peak desiccation tolerance in January or
February (Englert et al., 1993). Trees should be harvested during their desiccation

9

tolerance peak to aid in reducing water and carbohydrate stresses. With a lower
tolerance to desiccation the trees may become dried out and have issues with
establishing their root system and shoot and root dieback after transplant (Englert et al.,
1993).
The coarseness of a root system may explain why some species are more
tolerant to desiccation than others. In a study by Englert et al. (1993) red oak trees
were the most desiccation-tolerant and also had the coarsest root system of the three
species in the study. They describe that the larger roots would have a “lower surface
area to volume ratio,” which may have contributed to reduced water loss and able to
withstand longer desiccation periods. Exposure of the roots system to the atmosphere
after harvest can greatly reduce tree water status. Trees, if not protected, may lose
water resulting in desiccation in roots and shoots (Bates et al., 1994), which greatly
limits the reestablishment of roots and may cause significant dieback in shoots.
Different species may react differently to conditions during the pre-plant processes.
However, Murakami et al., (1990) found that in spite of the dramatic difference in
desiccation tolerance between species and cultivars, the rate of water loss from either
whole plants or root and stem tissues was similar.
Approach to dealing with transplant stress
The pre-plant storage and handling of bareroot trees are known to impair the rate of
root growth, carbohydrate status, or water status and will decrease the transplanted
trees survival (Watson & Himelick, 1982a). The treatments that nurseries employ help
to lessen or eliminate the stress on transplanted trees. These methods assist the

10

transplanted tree to break dormancy, increase root growth potential, and effectively
utilize carbohydrate reserves.
Heeling-in is a storage treatment used to aid in improved water status and root
regeneration. Heeling-in consists of placing the roots of the trees in a trenched section
of substrate or mulch, covering, and watering them in. Heeling-in has also been
described as “high-density planting in a furrow” (Strange et al., 2002). The treatment
reduces transplant shock and supports root regeneration (Starbuck et al., 2005).
Allowing the trees to sit in moist mulch for roughly one to four weeks can help the
survival rate of the trees after they are transplanted. In a study done by Struve (2009),
heeling the trees in pea gravel resulted in better root growth than in wood chips.
However, the trees in this study were left in the media for roughly six months. Strange
et al. (2002) states that leaving heeled-in trees for more than one season will increase
the difficulty of transplanting and decreases survivability. Concurring with Strange et al.,
(2002), Scianna et al., (2005) states that long-term storage of heeled-in plants will
increase stresses on the plants.
Storing bareroot trees in a cooler is another common nursery practice. If the
trees arrive from the wholesale nursery too early in the season to be planted, placing
them in cold-storage is beneficial. Some of the benefits include increased RGP after
transplanting, the tree’s ability to withstand colder temperatures, thus improving cold
hardiness, and increased growth rates after transplanting (Lundberg et al., 1990).
However, cold-storage has some drawbacks. These include drying out of the roots and
shoots, sub-optimal temperatures, loss of dormancy due to inappropriate temperatures,
and disease if not handled properly (Dozic, 2009). As cited by Murakami et al. (1990),

11

Webb and von Althen (1980) showed that moisture loss by broadleaf trees during cold
storage negatively affected their RGP and, subsequently, their survival and vigor.
Venator (1985) conducted a study on the effect storage had on shortleaf pine seedlings.
His results showed that the longer seedlings were in the storage treatments the lower
the survival rates were after planting. Lifting time of bareroot trees is also believed to
have an impact on cold-stored trees. Kozlowski & Davies (1975) found that lifting
seedlings in early fall and placing them in cold storage reduced RGP but increased it
when the seedlings were lifted in early winter. Similarly, Murakami et al. (1990) stated
that plants harvested during the dormant season, in general, were better able to
withstand postharvest handling and cold storage conditions. Also favorable for cold
storage, several studies also illustrate the need to cover the roots and/or the shoots
(Bates et al., 1994; Bates & Niemiera, 1996, 1997; Webb & Lakes, 1980) during cold
storage, which helps to reduce desiccation. Along with research that documents
reduced desiccation by covering roots and/or shoots, Bates & Niemiera, (1996) found
that coating shoots with wax prior to cold-storage significantly decreased desiccation.
This practice is commonly used for bareroot rose cranes. All of these beneficial
treatments proposed for cold-stored bareroot trees can increase their chances of
survival.
Sweating is another beneficial practice that forces bud break and active growth.
The main objectives are to rehydrate the root system by increasing the humidity and
temperature surrounding the plants (Halcomb & Fulcher, 2004). Common knowledge
regarding sweating seems to be that implementing it on many bareroot tree species is
beneficial but some trees are so deep in dormancy that they need to be sweated before

12

they can be transplanted (Bismarck Plant Materials Center, 2007). Desiccationintolerant species, including hackberry and Washington hawthorn, may benefit from the
breaking of dormancy and root rehydration (Murakami et al., 1990) that sweating
promotes increasing its survivability.
Misting is another technique used to rehydrate roots and shoots before and after
transplanting. The common nursery practice is to continuously spray with a water
source. Misting the trees is thought to increase the water potential of the tree. Bates &
Niemiera (1994) found that the water potential of desiccation-tolerant, Norway maple
(Acer platanoides L.) and desiccation-intolerant, Yoshino cherry (Prunus x yedoensis
Matsum.), increased when they were misted. The non-misted cherry trees were
deemed unmarketable. The misting treatment could be another beneficial technique to
improve the survivability of transplanted trees.
The pre-plant storage and handling of bareroot trees is important to the overall
success and survivability after transplanting. There is a connection between root
growth potential, water status, and carbohydrate status in the trees. Techniques used
to decrease root and shoot desiccation, increase root regeneration, and reduce stress
of transplant shock are widely used in the nursery industry. There is little published
scientific research on the physiological reasons why these treatments work to increase
survivability of bareroot landscape trees after they are transplanted.

13

APPENDIX 1

14

2010

B

2015

C

2020

detected before 2010

All satellite populations

A

Figure A1.1. Simulation of the emerald ash borer spread in counties from March 2010 to
March 2020 (base case). The maps represent the rounded average of 200 stochastic
simulations (Kovacs et al., 2011).

15

LITERATURE CITED

16

LITERATURE CITED

Baldwin, V. C., & Barney, C. W. (1976). Leaf Water Potential in Planted Ponderosa and
Lodgepole Pines. Forest Science, 22(3), 344–50.
Bates, R. M., & Niemiera, A. X. (1994). Mist Irrigation Reduces Post-transplant
Desiccation of Bare-root Trees. Journal of Environmental Horticulture, 12(1), 1–3.
Bates, R. M., & Niemiera, A. X. (1996). Effect of Transplanting on Shoot Water Potential
of Bare-root Washington Hawthorn and Norway Maple Trees. Journal of
Environmental Horticulture, 14(1), 1–4.
Bates, R. M., & Niemiera, A. X. (1997). Effect of Cold Storage and Pre-transplant
Desiccation on Root Growth Potential and Bud Break of Bare-root. Journal of
Environmental Horticulture, 15(2), 69–72.
Bates, R. M., Niemiera, A. X., & Seiler, J. R. (1994). Cold Storage Method Affects Root
and Shoot Water Potential of Bare-root Hawthorn and Maple Trees 1. Journal of
Environmental Horticulture, 12(4), 219–222.
Bismarck Plant Materials Center. (2007). Plant Chat, Spring 2007. Retrieved from
http://plant-materials.nrcs.usda.gov/ndpmc
Cabral, R., & O’Reilly, C. (2008). Physiological and field growth responses of oak
seedlings to warm storage. New Forests, 36(2), 159–170.
Canham, C. D., Kobe, R. K., Latty, E. F., & Chazdon, R. L. (1999). Interspecific and
intraspecific variation in tree seedling survival : effects of allocation to roots versus
carbohydrate reserves. Oecolgia, 121, 1–11.
Cleland, E. E. (2011). Biodiversity and Ecosystem Stability. Nature Education
Knowledge, 2(9).
Collins, A., & Mccullough, D. (2012). SLow Ash Mortality. Retrieved October 23, 2012,
from www.slameab.info
Davis, A. S., & Jacobs, D. F. (2005). Quantifying root system quality of nursery
seedlings and relationship to outplanting performance. New Forests, 30(2-3), 295–
311.
Dozic, M. (2009). Evaluating the Effects of Sweating on Bud Break and Survival and
Growth of Four Deciduous Tree Species.

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Englert, J. M., Warren, K., Fuchigami, L. H., & Chen, T. H. H. (1993). Antidesiccant
Compounds Improve the Survival of Bare-root Deciduous Nursery Trees. Journal of
the American Society for Horticultural Science, 118(2), 228–235.
Halcomb, M., & Fulcher, A. (2004). Sweating Nursery Stock To Break Dormancy.
Retrieved from http://www.ca.uky.edu/HLA/Dunwell/LnrSweat.html
Hall, C. R., Hodges, A. W., & Haydu, J. J. (2005). Economic Impacts of the Green
Industry in the United States (pp. 1–81). Retrieved from
www.utextension.utk.edu/hbin/greenimpact.html
Hallgren, S. W., & Tauer, C. G. (1989). Root growth potential, first-year survival, and
growth of shortleaf pine seedlings show effects of lift date, storage, and family.
Southern Journal of Applied Forestry, 13, 163–169.
Kobe, R. K. (1997). Carbohydrate allocation to storage as a basis of interspecific
variation in sapling survivorship and growth. Oikos, 80, 226–233.
Kovacs, K. F., Mercader, R. J., Haight, R. G., Siegert, N. W., McCullough, D. G., &
Liebhold, A. M. (2011). The influence of satellite populations of emerald ash borer
on projected economic costs in U.S. communities, 2010-2020. Journal of
Environmental Management, 92(9), 2170–81.
Kozlowski, T. T., & Davies, W. J. (1975). Control of water balance in transplanted trees.
Journal of Arboriculture, 1(1), 1–10.
Lundberg, J. D. D., Tabbush, P. M., Cannell, M. G. R., Sheppard, L. J., & Murray, M. B.
(1990). The Influence of Desiccation , Rough Handling and Cold Storage on the
Quality and Establishment of Sitka Spruce Planting Stock. Forestry, 63(2), 129–
141.
McKay, H. M. (1996). A review of the effect of stresses between lifting and planting on
nursery stock quality and performance. New Forests, 13, 363–393.
Murakami, P., Chen, T., & Fuchigami, L. H. (1990). Desiccation tolerance of deciduous
plants during postharvest handling. Journal of Environmental Horticulture, 8(1), 22–
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Ritchie, G. A. (1982). Carbohydrate reserves and root growth potential in Douglas-fir
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Ritchie, G. A. (1985). Root growth potential: principles, procedures and predictive
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predictive abilities of major tests, 93–105.

18

Scianna, J. D., Logar, R., & Ogle, D. (2005). Temporary storage and handling of
container, bareroot, and cutting stock. Plant Materials Technical Note, MT51(2005), 1–6.
Simpson, D. G., & Ritchie, G. A. (1996). Does RGP predict field performance? A
debate. New Forests, 13(1-3), 249–273.
Starbuck, C., Struve, D. K., & Mathers, H. (2005). Bareroot and balled and-burlapped
Red Oak and Green Ash can be summer transplanted using the Missouri Gravel
Bed System. Hort Technology, 15(1), 122–127.
Strange, C., Ogle, D., & St John, L. (2002). Tree Planting, Care and Management.
October (pp. 1–22). Boise.
Struve, D. K. (1990). Root Regeneration in Transplanted Deciduous Nursery Stock. Hort
Science, 25(3), 266–270.
Struve, D. K. (1996). Bare Root Shade Tree Whip Production in Containers. Journal of
Environmental Horticulture, 14(1), 13–17.
Struve, D. K. (2009). Tree Establishment: A Review of Some of the Factors Affecting
Transplant Survival and Establishment. Arboriculture and Urban Forestry, 35(1),
10–13.
United States Department of Agriculture. (2007). Nursery Crops 2006 Summary.
National Agricultural Statistics Service, 3(September).
Venator, C. R. (1985). Survival of Shortleaf Pine (Pinus echinata Mill.) Seedlings as
Influenced by Nursery Handling and Storage. USDA Forest Service, 17–19.
Watson, G. W., & Himelick, E. B. (1982). Seasonal variation in root regeneration of
transplanted trees. Journal of Arboriculture, 8(12), 305–310.
Webb, D. P., & Lakes, G. (1980). Storage of hardwood planting stock: effects of various
storage regimes and packaging methods on root growth and physiological quality.
New Zealand Journal of Forestry Science, 96(1), 83–96.

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CHAPTER TWO
PRE-PLANT STORAGE AND HANDLING OF DIFFICULT TO TRANSPLANT ASH
ALTERNATIVES

20

Abstract
The loss of ash (Fraxinus spp.) trees in the midwestern United States due to emerald
ash borer has emphasized the need for more diversity in urban and community forests.
However, nursery growers report that many Fraxinus spp. alternatives are difficult to
transplant. Understanding the physiological reasons why one tree species has superior
transplantability over another is an important factor in increasing production of Fraxinus
spp. replacements. In this study, we examined five difficult to transplant ash
alternatives; Celtis occidentalis, Quercus bicolor, Quercus ellipsoidalis, Quercus rubra,
Taxodium distichum, and Fraxinus americana. To mimic nursery grower practices,
trees were assigned at random to one of four treatments: 1) control, 2) heeled-in, 3)
cold storage, or 4) sweating. After treatment, trees were assigned at random to one of
three evaluations: root growth potential (RGP) test, container planting or field planting.
Root growth potential was very low for Quercus spp. trees and varied by treatment for
C. occidentalis. Taxodium distichum trees had a relatively high root growth potential in
all treatments. Stem water potential measured immediately before and after pre-plant
treatments suggest that Quercus spp. trees and T. distichum trees were able to
rehydrate during sweating while water stress levels in C. occidentalis trees remained
high. The results suggest that poor transplanting success reported for Quercus spp.
trees may be related to low root growth potential, whereas poor success of C.
occidentalis trees may be due to shoot desiccation during storage and handling.

21

Introduction
Outbreak of exotic invasive pests such as emerald ash borer (EAB; Agrilus
planipennis Fairmaire) and Dutch elm disease (Ophiostoma ulmi (Buisman) Nannf.)
highlight the need for improved diversity in urban and community forests. EAB has had
a major impact on landscapes of the midwestern United States. It is an invasive insect
that affects all species of the genus Fraxinus including popular landscape trees such as
green ash (F. pennsylvanica Marsh.) and white ash (F. americana). It was identified in
Detroit, Michigan in 2002 and thought to have arrived ten years earlier in cargo shipping
materials from Asia (Poland & Mccullough, 2006). EAB has devastated Fraxinus tree
populations killing tens of millions of trees in Michigan alone, with similar numbers in the
surrounding states (“www.emeraldashborer.info,” n.d.) An estimated cost for the
removal of these infested trees in the United States is between $20-$60 billion (Poland
& Mccullough, 2006). Ash trees were popular as landscape trees because of ease of
transplant and site adaptability. Ironically, ash trees were widely planted to replace elm
trees lost due to Dutch elm disease.
As Midwestern communities develop tree planting programs to replace tree cover
lost to EAB, university extension services and others have proposed viable ash
alternatives for nursery growers to reference (Cregg & Schutzki, 2004; Iles, 2012; Jull,
n.d.). Increasing diversity in urban and community landscape is important to prevent a
catastrophic loss like with the ash trees. Many urban and community forestry programs
cite the “10% rule” or “10-20-30 rule”; the rule states that no more than ten percent of a
given landscape should be planted with any one species (Santamour, 1990). Moreover,
the rule states that no more than 20% of any genus or 30% of any family be planted to

22

create a diverse community (Hanson, 1990). Many diseases and pests tend to choose
trees by family, where somewhat resistant species may harbor pests that could be
damaging to other species in the same family (Hanson, 1990). To accurately apply the
ten percent rule, full-stocking or planting all available tree planting sites of urban
landscapes must be applied not just 10% of what is currently planted (Ball et al., 2007).
Although the benefits of promoting species diversity in urban and community
forests is widely recognized, landscape nursery managers frequently note that many
ash alternatives are difficult to transplant or suffer some dieback in nursery production.
Widely recommended ash alternatives include oaks (Quercus spp.), hackberry (Celtis
occidentalis L.), baldcypress (Taxodium distichum (L.) Rich. var. distichum), maples
(Acer spp.), and lindens (Tilia spp.).
Dieback due to desiccation and poor root regeneration are major concerns for
nursery growers when trying to generate a marketable product. It is known that the
physiology of trees is affected when trees are transplanted. These physiological effects
are commonly referred to as ‘transplant shock’ or ‘transplant stress’ and are usually
evident in delayed bud-break, crown die-back, poor growth, or mortality. Transplant
stress may be caused by a variety of factors but is often linked to several interrelated
morpho-physiological characteristics including root growth potential, starch and
carbohydrate reserves, overall root-shoot allocation, dormancy status, and fine
root:coarse root ratios (Burdett, 1990; Davis & Jacobs, 2005; Haase & Rose, 1993;
McKay, 1996). Root growth potential is the ability of plants to initiate and elongate their
roots in a given environment (Ritchie, 1985). A low root growth potential is detrimental
to a transplanted tree because the rate at which the root regenerate may not be fast

23

enough to offset the transplant stress it will encounter (Watson & Himelick, 1982b).
Carbohydrate reserves are also important to counterbalance transplant stress. Ritchie
(1982) explains that a change stored plants undergo is a gradual respiratory depletion
of reserve sugars and starches. The loss of such reserves has been implicated in poor
tree survival and poor root growth potential (Ritchie, 1982).
Nursery growers have had limited success addressing transplanting problems
associated with many ash alternatives. In the midwestern United States, nurseries
commonly receive bareroot shade tree liners (small trees, five feet in height to two
inches in caliper) from propagation nurseries in Oregon in mid-March to mid-April.
Trees are often heeled-in mulch or held in cold storage prior to planting. Another
common practice is sweating which is thought to promote bud break and active growth.
The main objectives of sweating are to rehydrate the roots and to induce the tree to
break dormancy (Halcomb & Fulcher, 2004). Sweating the trees is believed to initiate
growth and is widely recommended. Dozic (2009), on the other hand, found that the
sweating method had no significant effects on either desiccation-tolerant or -intolerant
tree species. Little is known, however, about the physiology underlying this process.
The physiological basis for poor initial growth of common ash alternatives may be
related to lack of rehydration, inadequate carbohydrate reserves, or poor initial root
growth following transport and handling.
In this project we examined the effects of pre-plant handling on transplant stress
of five ash alternative species in a typical nursery production system. The goal of this
project was to improve the overall availability and success of important ash alternative
species in production nurseries to facilitate a more diverse urban landscape. The

24

objectives of this study were to: 1) determine the effect of pre-plant handling on initial
survival and growth of common ash alternatives and 2) determine the physiological
responses to pre-plant handling.

25

Materials and Methods
The project was conducted as two related studies; one conducted in 2010 and one
conducted in 2011. Experimental procedures are described for the 2010 study and
highlight changes for 2011.
2010 Season
Plant material and treatments
In April 2010, we received 256 bareroot liners (5-6’ whips/lightly branched liners) via
refrigerated truck from J. Frank Schmidt & Son Co. nursery (Boring, OR). The shipment
included 64 trees from each of four species: hackberry (C. occidentalis), swamp white
oak (Quercus bicolor Willd.; Q. bicolor), red oak (Quercus rubra L.; Q. rubra), and
baldcypress (T. distichum). Each tree was immediately tagged and assigned at
random to one of four treatments: 1) control, 2) heeling-in, 3) cold storage, or 4)
sweating (Table A2.1). All treatments, except control, were maintained for three weeks.
The control trees were assigned, directly off the truck, to three evaluations; field
planting, container planting, and root growth potential (RGP) test. The heeled-in
treatment was designed to simulate a common nursery practice of storing trees
outdoors prior to planting. We stood the trees up and covered the roots with container
substrate mix of pine bark-peat moss (80:20; v:v). Trees were watered with an
overhead sprinkler once a day. Trees in cold storage were placed in a 4oC (40oF) walkin cooler at the MSU Horticulture Teaching and Research Center (HTRC: Holt, MI).
Trees were situated upright in large wooden crates with their roots covered with straw
and watered as needed to prevent desiccation, approximately 4 times/wk. The
sweating treatment was designed to replicate a common nursery practice used to

26

stimulate growth on recalcitrant trees (Halcomb & Fulcher, 2004). Trees were placed
on the floor of a hoop greenhouse with double-walled poly (4 mil) at the MSU Forestry
Tree Research Center (TRC). Trees were alternated with layers of burlap and then
covered with a large sheet of white plastic. Burlap was checked daily and watered as
needed to prevent desiccation, approximately 4 times/wk. After treatments were
applied for 3 wks, trees were assigned at random to one of three evaluations: field
planting, container planting, and root growth potential test. We measured shoot water
potential using a pressure chamber (PMS Instrument Company, Albany, OR)
immediately before and after pre-plant treatments (Table A2.2).

Root Growth Potential (RGP) test
Root growth potential was evaluated by planting trees in a gravel culture system for
three weeks and determining new root growth. Control trees were placed in the gravel
culture system immediately upon receipt; trees in the three pre-plant treatments were
placed in the gravel culture system after 3 wks of treatment (Table A2.4). Trees were
planted in 25-gallon (95-liter) containers filled with clean pea-gravel in a hoop
greenhouse with double-walled poly (4 mil) at the TRC. Four trees, one from each
treatment x species combination, were planted in each container with eight replications.
Root systems were kept moist using a micro-sprinkler system controlled by an
automatic timer. Irrigation was set to run for 8 s every 16 min. Initial tree height and
stem diameter were measured at planting. Stem diameter was measured with a caliper
3” above the graft union on the C. occidentalis, Q. bicolor, and Q. rubra and 6” above
the root collar on the T. distichum. New shoot growth or stem dieback was determined

27

at the end of the RGP test. Stem dieback was estimated as the distance from the tip of
the terminal shoot to the highest living bud. After 3 wks the trees were removed from
the gravel and new root growth was assessed by counting the number of new white
roots and measuring root lengths of a random sample of ten new roots. Total new root
length was estimated as number of new roots x average new root length. All new roots
were harvested and dried in an oven at ~75ºC for approximately 1 wk. The dried roots
were then weighed.

Field and container planting
We planted four trees from each species x treatment combination, including control
trees, in a field block at the Sandhill farm section of the HTRC. Trees were planted in
two rows, 3’ (0.91 m) on center (Table A2.4). Soil type at the site was sandy loam. We
planted an additional four trees per species x treatment combination, including control
trees, in 15-gallon (57-liter) container filled with a mixture of pine bark and peat moss
(80:20, v:v). Trees were watered by hand approximately 2 times/wk.

Growth and physiology
Height and stem diameter were measured at initial planting and at the end of the
growing season of field-grown, and container-grown trees. Stem diameter was
measured with a caliper 3” above the graft union on the C. occidentalis, Q. bicolor, and
Q. rubra and 6” above the root collar on the T. distichum. Stem dieback was estimated
as the distance from the top-most portion of the terminal leader to the point where
current season growth initiated.

28

We measured pre-dawn and mid-day stem water potential using a pressure chamber on
field and container-grown trees. We measured chlorophyll fluorescence (ratio of
variable fluorescence to maximal fluorescence; Fv/Fm) on the leaves using an OS-30p
Chlorophyll Fluorometer (Opti-Science, Hudson, NH). Leaves were dark acclimated for
10 min prior to measurement. All growth and physiological measurement dates are
listed in Table A2.2.
2011 Season
Plant material and treatments
In April 2011, we received 316 bareroot liners (5-6’ whips/lightly branched liners) via
refrigerated truck from J. Frank Schmidt & Son Co. The shipment included 64 trees
from each of four species: C. occidentalis, Q. rubra, and T. distichum, white ash
(Fraxinus Americana L.), and 60 trees of northern pin oak (Quercus ellipsoidalis E.J.
Hill). Quercus ellipsoidalis (Q. ellipsoidalis) was substituted for Q. bicolor because of
supply issues at the liner production nursery and white ash (F. americana), which is
widely considered as easy to transplant, was included as a positive control.
We collected samples and took pressure chamber readings on trees before and after
lifting, at the liner production nursery in Oregon. Pre-harvest samples were taken on
February 3, 2011. Post-harvest samples were taken on March 31, 2011. Shoot and root
samples that were collected on both dates for carbohydrate analysis and were
packaged in a cooler with dry ice and shipped to Michigan State University.
The same pre-planting treatments were executed on the trees as in the 2010 season
(Table A2.1).

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RGP test
The root growth potential test of the control trees was put through the same methods as
the 2010 season (Table A2.5).

Field and container planting
Field and container planting was the same as the 2010 season (Table A2.5). The field
trees had an irrigation line setup to run approx. once per day for 10 min.

Growth and physiology
Height, stem diameter, dieback, water potential, gas exchange, and chlorophyll
fluorescence were measured the same as the 2010 season (Table A2.3).

Carbohydrate analysis
Shoot and root samples of the trees were collected at J. Frank Schmidt & Son Co. for
pre-harvest analysis on February 3 and post-harvest analysis on March 31. Total nonstructural carbohydrate content was analyzed using the DuBois phenol-sulfuric acid
method (DuBois et al., 1956). Dubois describes that when “phenol [is] in the presence
of sulfuric acid [it] can be used for the quantitative colorimetric microdetermination of
sugars and their methyl derivatives, oligosaccharides, and polysaccharides.” D-glucose
was used for the standard curve.

Statistical analyses

30

For both years, effects of treatment, species, and interaction of species and treatment
on each response variable were evaluated by Analysis of Variance. Data were
analyzed as a completely randomized design using the model γijk=m+αi+βi+αβij=εijk;
where γijk=response variable; αi=species effect; βi=treatment effect; and ε=experimental
error. Where significant (p<0.05) species or treatment effects were indicated, means
were separated by Tukey’s studentized range test.

31

Results
2010 Season
Pre-plant water status
The initial water potential (Ψw) of shoots of all the tree species was relatively low upon
arrival from the Oregon nursery, ranging from -1.5 for the T. distichum trees to -3.7 for
the C. occidentalis trees (Figure A2.1). The pre-plant treatments did not consistently
improve water status. Trees that were cold-stored had the overall lowest Ψw. Heelingin improved water status of C. occidentalis trees compared to the untreated controls.
The two Quercus species showed water status recovery with the sweating treatments
compared to the control treatment. Taxodium distichum trees had the highest Ψw and
were unresponsive to treatments except for reduced water status during cold-storage
(Figure A2.1).

Root growth potential
New root growth potential (RGP) varied by species but was not affected by pre-plant
treatments. Taxodium distichum trees produced the highest number of new roots while
both Quercus species showed consistently low RGP, generating less than 30 new roots
per tree during the 3-week RGP test (Figure A2.2). Celtis occidentalis trees that were
heeled-in prior to the RGP test produced an average of 180 new roots.

Shoot growth/stem dieback

32

Our experimental protocol provided three opportunities to evaluate shoot growth (or
stem dieback) in response to pre-plant treatments: shoot growth during the RGP test,
growth during and after container-planting and growth after field-planting. In general,
pre-plant treatments had little effect on stem growth or dieback after planting although
there were a few exceptions to this trend. In the container-planted trial, sweating
increased stem dieback for Q. bicolor, Q. rubra, and especially C. occidentalis trees
(Figure A2.3). In the field-planted trial, C. occidentalis and Q. bicolor trees experienced
significant dieback at the end of the season (Figure A2.4). All of the T. distichum trees
died in this trial due an intermediate undetected irrigation system failure. Quercus rubra
trees showed the highest growth of any species. In the root growth potential trial,
species affected shoot growth in trees of both Quercus species showing net growth.
The interaction of species and pre-plant treatments was significant (<0.05) due to
increased stem dieback for C. occidentalis trees that had been sweated and T.
distichum trees that had not been subjected to any pre-plant treatments (Figure A2.5).

Post-planting physiology
Predawn and midday water potential (Ψw) of container-grown trees varied among
species (Table A2.6). Taxodium distichum trees had the highest Ψw for both predawn
and midday readings and C. occidentalis trees had the lowest. Pre-plant treatments
had relatively little effect on Ψw of container-grown trees and treatments did not improve
water status for any trees of any species. No differences between species or
treatments were found for the predawn and midday Ψw evaluation of the field-planted

33

trees. The missing values for T. distichum trees are due to the Ψw exceeding the limits
of the pressure chamber we used (Table A2.7).
Neither species nor pre-plant treatment affected (p<0.05) chlorophyll fluorescence
(Fv/Fm) of trees planted in containers on the early season (June 29) measurements
(Table A2.8). On the late-season measurement date (Sept. 1), however, cold-storage
or sweating before planting reduced Fv/Fm for trees of most species. Quercus bicolor
and T. distichum trees had higher values than the other species and the cold-stored and
sweated trees showed no benefit (Table A2.8). Pre-plant treatments and species did
not affect Fv/Fm of field-planted on either measurement date (Table A2.9).
2011 Season
Carbohydrate analysis
Total nonstructural carbohydrates (TNC) of root and shoot tissue varied with species
and time of sample collection. Nonstructural carbohydrate concentration of root tissue
of most trees increased from the initial sample and the post-harvest sample. Celtis
occidentalis and F. americana trees were the exception with a decrease and no change
respectively (Figure A2.6). The total nonstructural carbohydrates in the shoots showed
that was no change between the pre- and post-harvested trees. Fraxinus americana
trees were the exception with a decrease in carbohydrates between the two dates
(Figure A2.7). Quercus species had lower root TNC than trees of the other species,
especially before lifting, and Q. ellipsoidalis trees had the lowest TNC of all trees
sampled.

Pre-plant water status

34

Stem Ψw of all trees decreased (p<0.05) from the time they were lifted at the liner
nursery in Oregon (post-harvest) until they arrived on the truck in East Lansing (Control)
(Figure A2.8). This indicates significant water loss occurred from when the trees were
harvested and during storage and shipping. Species varied in their ability to re-hydrate
during the pre-plant treatments. Quercus rubra trees showed significant Ψw recovery
after heeling-in and sweating. In contrast, sweating reduced Ψw of C. occidentalis
trees.

Root growth potential
Root growth potential (RGP) varied among species but not treatments within species.
Fraxinus americana and T. distichum trees showed significantly higher root numbers
throughout all the treatments than trees of the other species. Trees of both of the
Quercus species had consistently low root regeneration across all pre-plant treatments
(Figure A2.9).

Shoot growth/stem dieback
Tree growth responses to pre-plant treatments varied by species and differed among
the evaluation plantings. In the container-planted trial, pre-plant treatments did not
improve stem growth relative to the control for any species (Figure A2.10). Celtis
occidentalis trees showed dieback in all treatments. Sweating trees before planting
reduced growth of F. americana trees. The field-planted trees experienced dieback
across all species excluding F. americana trees. Fraxinus americana trees showed

35

growth in all treatments but no pre-plant treatment showed benefits. The cold storage
pre-plant treatment reduced dieback of field-planted T. distichum trees (Figure A2.11).
In the RGP trial most trees had some net shoot growth. The two significant exceptions
were the dieback of trees in the control treatment of C. occidentalis trees, establishing
the pre-plant treatments were beneficial and the dieback of the cold storage treatment
on F. americana trees showed evidence that it was not beneficial (Figure A2.12).

Post-planting physiology
Pre-plant treatments did not affect (p>0.05) predawn or midday Ψw of trees in either
the container-planted trial or in the field-planted trials (Tables A2.10 & A2.11). Water
potentials varied among species in both trials. Quercus ellipsoidalis trees had more
negative predawn Ψw than the other species in the field-planted trial. By midday,
however, Q. rubra and F. americana trees had similar Ψw levels. In the containerplanted trial, T. distichum trees has the least negative pre-dawn Ψw and had relatively
less negative midday Ψw, along with F. americana trees.
Pre-plant treatments did not affect chlorophyll fluorescence (Fv/Fm) of containerplanted or field-planted trees (Tables A2.12 & A2.13). For container-planted trees,
Fv/Fm did not vary among species. Species affected (p<0.05) Fv/Fm on both
measurements dates in 2011 in field-planting. Fraxinus americana and T. distichum
trees had relatively high Fv/Fm compared to C. occidentalis and Q. ellipsoidalis trees in
June. By the end of the summer, however, Fv/Fm was lower for F. americana trees
than for T. distichum trees.

36

Discussion
This research was conducted to evaluate methods to increase the survivability of
bareroot tree liners after lifting and prior to transplanting of ash alternatives.
Implementation of effective pre-plant treatments could aid in enhancing species
diversity through increased survivorship and faster growth of a diverse group of
landscape trees. Poor survival or extensive dieback of trees following transplanting has
been linked to a variety of factors including desiccation, poor carbohydrate status, or
ability to regenerate new roots (Lundberg et al.,1990; McKay, 1996; Scianna et al.,
2005).
2010 Season
Results of the first-year trials showed no defined trends within species in
response of the trees in response to the pre-plant treatments. There were no definite
trends within the treatments. In general, the initial Ψw of the sweating treatment was
less negative between species and the cold storage was more negative compared to
the other treatments. These differences may be due to the moist environment that the
sweated trees were subjected to, compared to the cold-stored trees, which were not
inflicted to such an irriguous environment. There were significant differences seen
between C. occidentalis trees and T. distichum trees. Celtis occidentalis trees had
more negative Ψw values than T. distichum trees. The data reveals that T. distichum
trees was better at maintaining a less negative Ψw than the other species and,
therefore, was initially under less stress.

37

There was a high amount of dieback of the sweating treatments in both the
container- and field-grown trees. The trees that were implemented with the sweating
treatments showed little difficulty regenerating new roots in any of the species. Celtis
occidentalis trees had the poorest response to the sweating treatment, which resulted in
more negative Ψw, shoot dieback in the field and in containers, and shoot dieback in the
root growth potential test. Young C. occidentalis trees have a fibrous root system and
Struve (1990) states that “species with fibrous root systems are easier to transplant than
species with coarse root systems.” Yet, we saw that C. occidentalis trees’ ability to
transplant was one of the most difficult. This may be from the stress implemented on
them during the treatments and after transplant.
Quercus rubra trees had low RGP compared to the other species, but they grew
relatively well in the container, field, and RGP plantings. This may be from the larger
roots and available carbohydrates stored in the roots. The initial Ψw of Q. rubra trees
for all treatments was relatively high. The trees were better able to retain water in their
shoots. The high Ψw in the shoots at the time of transplanting could also explain the
growth seen in the plantings.
Quercus bicolor trees had similar Ψw, RGP heights, and root numbers as Q.
rubra trees but the species did not grow as well in the container- and field-grown trees
as the Q. rubra trees. The differences seen between these two species may be due to
their specific soil type. Quercus bicolor grow best in moist to wet soils (wetlands) while
Q. rubra perform best in well-drained soils (Rogers, 1990; Sander, 1990). The soil type
at our field-planted location was a well-drained sandy soil and the substrate for the

38

container-planted was a pine bark-peat moss blend, also well-drained (as stated in the
materials and methods). This soil/substrate type is not conducive to Q. bicolor trees’
natural soil habitat possibly causing the lack in growth.
Taxodium distichum trees had the highest Ψw and greatest root number but
showed very little growth in the container-grown test and all the trees died in the fieldgrown test. The complete mortality of the T. distichum trees in the field may be due to
irrigation failure during the growing season. The irrigation failure seemed to cause all
the T. distichum trees mortality but C. occidentalis trees showed significantly high shoot
dieback, Q. bicolor trees showed a small amount of shoot dieback but no growth across
all treatments, and Q. rubra trees showed growth across all treatments. This shows that
T. distichum trees could not overcome drought stress, even though they had a high
amount of root regeneration, while the other species did overcome the drought stress
and survived.
Chlorophyll fluorescence was used as an overall stress indicator of our trees. It
is considered a rapid and non-destructive method of measuring stress (Rose & Haase,
2002). The optimum value for a fluorescence reading is 0.83 Fv/Fm (Hunt, 2003) and
highly stressed readings are less than 0.60 (Ritchie, 2006). The chlorophyll
fluorescence of all the tree species had sub-optimal values, this means that the trees
were under environmental stresses. In the container-planted trees there were no
differences seen between the species and the treatments in June 2010 but in
September 2010 there were variations among species and treatments. Quercus bicolor
trees and T. distichum trees showed higher Fv/Fm values than the other two species,
coincidentally, those two species showed the most growth. In the field-planted trees,

39

there were no differences seen between the treatments and the species fluorescence
values for the two dates indicating all the species were exposed to the same amount of
stress. As stated above, T. distichum trees did not survive the field planting.
Bareroot trees may have the ability to generate new roots, as all the trees did,
they may not be able to rehydrate their shoots when transplanted, causing stress and
dieback.
2011 Season
Total nonstructural carbohydrate (TNC) data illustrated that the pre- and postharvest values did not change in the shoots. There were, however, species differences.
Celtis occidentalis trees had the lowest amount of TNC, followed by T. distichum trees,
the Quercus spp., and F. americana trees, which had the highest. Storage conditions
are one of the main reasons for carbohydrate depletion (McKay, 1996). The unchanged
pre- and post-harvest values of TNC in the shoots are evidence that the storage method
at the wholesale level is adequate. The TNC of the roots, however, tell a different story.
There was an increase of TNC from pre-harvest to post-harvest for the Quercus spp.
and T. distichum. Fraxinus americana trees had no differences between the harvest
dates and C. occidentalis trees had a decrease. In a study conducted by Girard et al.
(1997), Acer rubrum bareroot seedlings did not show significant depletion of TNC after
12 days of exposure to ambient conditions. The bareroot trees in this study were stored
outside in sawdust for ~50 days in late winter in Oregon. These differences may be
attributed to the reallocation of TNC to the roots for an increase and respiration of the
trees for a decrease.

40

The water potential (Ψw) values of the bareroot trees at post-harvest were less
negative than when the trees arrived at Michigan State University (control treatment).
This shows that a significant amount of water loss occurred while the trees were in predelivery storage and on the delivery truck. After the pre-plant treatments were imposed
the water status of the trees seemed to improve to pre- and post-harvest Ψw values, as
compared to the control group. This trend was detected in T. distichum trees and Q.
rubra trees, more specifically in the heeled-in and sweated trees of Q. rubra trees. An
observed exception was the sweated treatment which revealed the Ψw exceeded the
limit of the pressure chamber for C. occidentalis trees and Q. ellipsoidalis trees (-4.0
MPa). The high levels of water stress may be attributed to the trees drying out or not
being adequately watered during the sweated treatment period. The Quercus spp. and
C. occidentalis trees in the 2010 season did not see the high levels of water stress
during the sweating treatment nor did Quercus rubra trees in the 2011 season. These
data suggest that conditions immediately before and during transport are critical to
maintaining the trees water status.
All the tree species exhibited root regeneration in the root growth potential (RGP)
planting. Fraxinus americana trees and T. distichum trees had the highest amount of
new root growth. Despite having the highest amount of new root growth, the least
negative Ψw, and a higher root TNC post-harvest, T. distichum trees had the least
amount of growth in the RGP planting and the field planting. Furthermore, T. distichum
trees had the most growth in the container planting. This may be explained by the type
of environment they favor. Taxodium distichum does best in moist to wet soils and are

41

not conducive to dry or drought conditions (Elcan & Pezeshki, 2002) and they favor an
organic substrate over a sandy soil (Day et al., 2006), which was our field conditions.
Taxodium distichum trees may have not done well in the RGP planting because of the
highly porous pea gravel used.
The Quercus spp. trees had consistently low new roots but still had significant
growth in the RGP planting. Quercus ellipsoidalis trees in the sweated treatment that
exceeded the limits of the pressure chamber with highly negative Ψw had significant
shoot growth. This may be due to the Quercus spp. ability to rehydrate their shoots and
their tolerance to desiccation (Englert et al., 1993).
There was growth of the container-grown trees except for C. occidentalis trees.
Celtis occidentalis trees showed the ability to generate new root growth but then
exhibited dieback or mortality when planted in containers or in the field. This may be
due to the significant water stress the trees were under when transplanted after the preplant treatments especially the sweating. Also, the pre-dawn and midday Ψw for C.
occidentalis trees were the most negative of any species in the container-grown trees
but similar to the other species in the field planted. Taxodium distichum trees had
similar results in the field-grown planting; the trees were able to regenerate new roots
but then died in the field. However, T. distichum trees had the least negative Ψw after
the treatments were implemented and for the predawn/midday Ψw and the containergrown trees had significantly more growth than the other species. There was erratic
irrigation failure in the field but not to the extent of the 2010 season. Taxodium
distichum trees survived in the 2011 season, unlike the 2010 season, but had significant

42

shoot dieback. Taxodium distichum trees had significant growth in the containerplanting, demonstrating that drought stress had a major impact on the survivability of
the trees.
The chlorophyll fluorescence of the trees in the container-planting had somewhat
sub-optimal values but did not differ among species or treatments. However, the fieldplanting showed differences between species. Celtis occidentalis trees had the lowest
values indicating that they were under more stress than the other tree species. The
chlorophyll fluorescence data point out that the container-planted trees are less
stressed than the field-planted trees.
Fraxinus americana trees, the positive control, performed as we would have
expected. The trees had significant growth in all three plantings, exhibited high amount
root regeneration, and had high chlorophyll fluorescence values.

43

Conclusion
This research demonstrated the use of pre-plant treatments on bareroot tree
liners. The need for the trees to rehydrate after post-harvest is an important factor for
their survivability. Our study shows that the pre-plant treatments did help to rehydrate
the shoots and induce root regeneration.
Species behave differently, and different pre-plant treatments could benefit them
differently. The sweating treatment showed no benefit to the survivability of the species
but aided in the regeneration of new roots. Taxodium distichum trees exhibited a high
amount of root regeneration but when exposed to drought conditions showed severe
dieback and death. Fraxinus americana had similar amounts of root regeneration but
when exposed to the same drought condition still showed growth across all treatments.
Other pre-plant treatments, such as misting/soaking or applying a wax coating to the
bareroot trees, could also improve the growth and survival. Further research is needed
to document the effect of the pre-plant treatments on ash alternative species.

44

APPENDIX 2

45

Table A2.1. Overview of plant material, pre-plant treatments and evaluations of 20102011 pre-plant storage and handling tests.

Plant Material
2010
C. occidentalis
Q. rubra
Q. bicolor
T. distichum

2011
C. occidentalis
Q. rubra
Q. ellipsoidalis
T. distichum
F. americana

Pre-plant treatment
Control
Heeled-in
Cold storage
Sweat

Evaluation
Field-planted (4 trees/spp)
Container-planted (4 trees/spp)
Root growth potential (8 trees/spp)

46

Table A2.2. Growth and physiology measurement dates 2010.
Unassigned
Planting
Pre-treatment
water potential

Container
Planting

April 23

Post-treatment
water potential

Field
Planting

May 19

Height
measurement

May 20 &
August 13

May 20 &
August 13

Pre-dawn
water potential

July 23

July 23

Mid-day
water potential

July 23

July 23

July 14 &
August 13

July 14 &
August 13

June 29 &
September 1

June 29 &
September 1

Gas
exchange
Chlorophyll
Fluorescence

47

Table A2.3. Growth and physiology measurement dates 2011.
Unassigned
Planting

Field
Planting

Container
Planting

May 13 &
November 4

May 13 &
November 4

Pre-dawn
water potential

July 21

July 21

Mid-day
water potential

July 21

July 21

Gas
exchange

June 29 &
July 25

June 17 &
August 5

Chlorophyll
Fluorescence

June 16 &
August 24

June 16 &
August 24

Pre-treatment
water potential

April 18

Post-treatment
water potential

May 11

Height
measurement

48

Table A2.4. Schedule of treatments and evaluations for pre-plant handling trial 2010.
Treatment

Evaluation test

Date In

RGP Test

April 22

RGP Test

May 18
May 17

Container-planting

May 17

Placed in TRMT

April 22

RGP Test

May 18

Field-planting

May 17

Container-planting

May 17

Placed in TRMT
Sweating

April 23

Field-planting

Cold storage

April 23

Placed in TRMT
Heeled-in

Field-planting
Container-planting

Control

April 24

April 22

RGP Test

May 18

Field-planting

May 17

Container-planting

May 17

Date Out

49

May 14

June 11

June 11

June 11

Table A2.5. Schedule of treatments and evaluation tests for pre-plant handling trial
2011.
Treatment
Evaluation test
Date In
Date Out
RGP Test

April 14
April 15

Placed in TRMT
Heeled-in

Field-planting
Container-planting

Control

April 13

April 13

RGP Test

May 11

Field-planting

May 4

Placed in TRMT
Cold storage

April 12

RGP Test

May 11

Field-planting

June 7

May 6

Container-planting

May 4

Placed in TRMT
Sweating

June 7

May 6

Container-planting

May 9

April 12

RGP Test

May 11

Field-planting

May 5

Container-planting

May 6

50

June 7

Table A2.6. Mean predawn and midday water potential (Ψw) of container-grown
bareroot tree liners subjected to four pre-plant treatments. July 23, 2010.

Treatment
Control
Heel
Store
Sweat

Predawn shoot Ψw (MPa)
C. occidentalis
Q. bicolor
Q. rubra
-0.28a
-0.53a
-0.39a
-0.50b
-0.50a
-0.93a
-0.25a
-0.96a
-0.43a
na
-1.09a
-0.83a
AB
B
AB

T. distichum
-0.13a
-0.29a
-0.25a
-0.23a
A

Treatment
Control
Heel
Store
Sweat

Midday shoot Ψw (MPa)
C. occidentalis
Q. bicolor
Q. rubra
-1.90a
-1.20a
-0.79a
-1.89a
-1.45a
-1.94b
-1.94a
-1.40a
-1.15ab
na
-2.15a
-1.89b
C
B
B

T. distichum
-0.95a
-1.16a
-1.10a
-1.23a
A

Note: means within a column followed by the same lowercase letter are not different
(p<0.05). Species mean within a row followed by the same uppercase letter are not
different (p<0.05). Mean separation by Tukey’s studentized range test.

51

Table A2.7. Mean predawn and midday water potential (Ψw) of field-grown bareroot tree
liners subjected to four pre-plant treatments. July 23, 2010.

Treatment
Control
Heel
Store
Sweat

Predawn shoot Ψw (MPa)
C. occidentalis
Q. bicolor
Q. rubra
-0.83a
-1.25a
-1.43a
-0.65a
-0.73a
-2.75a
-0.80a
-1.78a
-2.71a
-0.80a
na
-1.40a
A
A
A

T. distichum
na
na
-0.90a
na
A

Treatment
Control
Heel
Store
Sweat

Midday shoot Ψw (MPa)
C. occidentalis
Q. bicolor
Q. rubra
-2.17a
-1.88a
-2.50a
-2.63a
-2.58a
-3.33a
-1.95a
-1.80a
-2.63a
-2.35a
-3.75a
-2.60a
A
A
A

T. distichum
na
na
-1.90a
na
A

Note: means within a column followed by the same lowercase letter are not different
(p<0.05). Species mean within a row followed by the same uppercase letter are not
different (p<0.05). Mean separation by Tukey’s studentized range test.

52

Table A2.8. Mean chlorophyll fluorescence of container-grown bareroot tree liners
subjected to four pre-plant treatments for two dates; June 29, 2010 and September 1,
2010.

Treatment
Control
Heel
Store
Sweat

Maximum quantum efficiency (Fv/Fm)
C. occidentalis
Q. bicolor
Q. rubra
T. distichum
0.735a
0.744a
0.709a
0.723a
0.731a
0.684b
0.739a
0.710a
0.730a
0.740a
0.736a
0.698a
0.762a
0.729a
na
0.726a
A
A
A
A

Treatment
Control
Heel
Store
Sweat

Maximum quantum efficiency (Fv/Fm)
C. occidentalis
Q. bicolor
Q. rubra
T. distichum
0.738a
0.788a
0.766a
0.808a
0.747a
0.767a
0.717ab
0.780ab
0.648b
0.732ab
0.678ab
0.741b
0.710ab
0.680b
0.652b
0.742b
B
A
B
A

Note: means within a column followed by the same lowercase letter are not different
(p<0.05). Species mean within a row followed by the same uppercase letter are not
different (p<0.05). Mean separation by Tukey’s studentized range test.

53

Table A2.9. Mean chlorophyll fluorescence of field-grown bareroot tree liners subjected
to four pre-plant treatments for two dates; June 29, 2010 and September 1, 2010.

Treatment
Control
Heel
Store
Sweat

Maximum quantum efficiency (Fv/Fm)
C. occidentalis
Q. bicolor
Q. rubra
T. distichum
0.714a
0.666a
0.690a
0.679a
0.746a
0.714a
0.719a
0.680a
0.722a
0.709a
0.712a
0.761a
na
0.662a
0.716a
na
A
A
A
A

Treatment
Control
Heel
Store
Sweat

Maximum quantum efficiency (Fv/Fm)
C. occidentalis
Q. bicolor
Q. rubra
T. distichum
0.769a
0.799a
0.755a
na
0.780a
0.781a
0.673a
na
0.763a
0.774a
0.708a
na
0.769a
0.769a
0.710a
na
A
A
A
na

Note: means within a column followed by the same lowercase letter are not different
(p<0.05). Species mean within a row followed by the same uppercase letter are not
different (p<0.05). Mean separation by Tukey’s studentized range test.
The missing values for T. distichum are due to the irrigation issues and zero survival of
the trees.

54

Table A2.10. Mean predawn and midday water potential (Ψw) of container-grown bareroot tree liners subjected to four
pre-plant treatments. July 21, 2011.

Treatment
Control
Heel
Store
Sweat

Treatment
Control
Heel
Store
Sweat

C. occidentalis
-1.18a
-1.51a
-0.98a
-1.03a
C

Predawn shoot Ψw (MPa)
F. americana
Q. ellipsoidalis
-1.24a
-1.19a
-1.31a
-1.12a
-1.31a
-0.93a
-1.23a
-1.08a
C
BC

Q. rubra
-1.01a
-0.79a
-0.91a
-1.12a
B

T. distichum
-0.63a
-0.75a
-0.66a
-0.72a
A

C. occidentalis
-2.35a
-2.18a
-2.07a
-2.23a
BC

Midday shoot Ψw (MPa)
F. americana
Q. ellipsoidalis
-1.66a
-2.49a
-2.09a
-2.64a
-1.88a
-2.15a
-1.95a
-2.75a
AB
C

Q. rubra
-2.09a
-2.28a
-2.06a
-2.41a
BC

T. distichum
-1.72a
-1.88a
-1.81a
-1.77a
A

Note: means within a column followed by the same lowercase letter are not different (p<0.05). Species mean within a row
followed by the same uppercase letter are not different (p<0.05). Mean separation by Tukey’s studentized range test.

55

Table A2.11. Mean predawn and midday water potential (Ψw) of field-grown bareroot tree liners subjected to four preplant treatments. July 21, 2011.

Treatment
Control
Heel
Store
Sweat

Treatment
Control
Heel
Store
Sweat

C. occidentalis
-1.25a
-1.48a
-1.40a
-1.34a
A

Predawn shoot Ψw (MPa)
F. americana Q. ellipsoidalis
Q. rubra
-1.18a
-2.05a
-2.00a
-1.30a
-2.10a
-1.13a
-1.37a
-4.00a
-1.50a
-1.29a
-2.60a
-1.50a
A
B
A

T. distichum
-0.83a
na
na
na
A

C. occidentalis
na
-1.38a
-2.13a
-1.68a
A

Midday shoot Ψw (MPa)
F. americana Q. ellipsoidalis
Q. rubra
-2.52a
-3.53a
-3.15a
-2.40a
-2.63a
-2.55a
-2.48a
-2.85a
-2.80a
-2.35a
-2.20a
-3.02a
AB
B
B

T. distichum
-2.58a
-3.90a
na
na
B

Note: means within a column followed by the same lowercase letter are not different (p<0.05). Species mean within a row
followed by the same uppercase letter are not different (p<0.05). Mean separation by Tukey’s studentized range test.

56

Table A2.12. Mean chlorophyll fluorescence of container-grown bareroot tree liners subjected to four pre-plant treatments.
June 16, 2011.

Treatment
Control
Heel
Store
Sweat

C. occidentalis
0.741a
0.738a
0.709a
0.745a
A

Maximum quantum efficiency (Fv/Fm)
F. americana Q. ellipsoidalis
Q. rubra
0.759a
0.753a
0.760a
0.761a
0.758a
0.731a
0.766a
0.767a
0.717a
0.735a
0.745a
0.737a
A
A
A

T. distichum
0.770a
0.712a
0.768a
0.774a
A

Note: means within a column followed by the same lowercase letter are not different (p<0.05). Species mean within a row
followed by the same uppercase letter are not different (p<0.05). Mean separation by Tukey’s studentized range test.

57

Table A2.13. Mean chlorophyll fluorescence of field-grown bareroot tree liners subjected to four pre-plant treatments for
two dates; June 16, 2011 and August 24, 2011.

Treatment
Control
Heel
Store
Sweat

C. occidentalis
0.717a
0.690a
0.687a
0.635a
C

Maximum quantum efficiency (Fv/Fm)
F. americana Q. ellipsoidalis
Q. rubra
0.764a
0.746a
0.719a
0.747a
0.727a
0.692a
0.731a
0.740a
0.726a
0.766a
0.730a
0.691a
A
AB
BC

T. distichum
0.765a
0.763a
0.766a
0.768a
A

Treatment
Control
Heel
Store
Sweat

C. occidentalis
0.772a
0.752a
0.749a
0.736a
AB

Maximum quantum efficiency (Fv/Fm)
F. americana Q. ellipsoidalis
Q. rubra
0.697a
0.780a
0.737a
0.718a
0.744a
0.748a
0.719a
na
0.724a
0.745a
0.727a
0.757a
B
AB
AB

T. distichum
na
na
0.786a
0.779a
A

Note: means within a column followed by the same lowercase letter are not different (p<0.05). Species mean within a row
followed by the same uppercase letter are not different (p<0.05). Mean separation by Tukey’s studentized range test.

58

Figure A2.1. Mean initial water potential of bareroot tree liners subjected to four preplant treatments prior to planting in 2010.
Note: spp: p<0.001, trmt: p<0.05, spp x trmt: p<0.05

59

Figure A2.2. Mean root number of root growth potential-grown bareroot tree liners
subjected to four pre-plant treatments in 2010.
Note: spp: p<0.001; trmt: ns; spp x trmt: ns

60

Figure A2.3. Mean growth/dieback of container-grown bareroot tree liners subjected to
four pre-plant treatments in 2010.
Note: spp: p<0.001, trmt: p<0.05, spp x trmt: p<0.05

61

Figure A2.4. Mean growth/dieback of field-grown bareroot tree liners subjected to four
pre-plant treatments in 2010.
Note: Baldcypress data not shown due to death of all trees. spp: p<0.001; trmt: p<0.05;
spp x trmt: p<0.05

62

Figure A2.5. Mean growth/dieback of root growth potential-grown bareroot tree liners
subjected to four pre-plant treatments in 2010.
Note: spp: p<0.001; trmt: ns; spp x trmt: p<0.05

63

Figure A2.6. Mean total non-structural carbohydrate content of roots of bareroot tree
liners collected pre- and post-lifted in 2011.
Note: spp: p<0.001; time: p<0.0001

64

Figure A2.7. Mean total non-structural carbohydrate content of shoots of bareroot tree
liners collected pre- and post-harvest in 2011.
Note: spp: p<0.001; time: p<0.05

65

Figure A2.8. Mean water potential of bareroot tree liners prior to lifting (pre-lift), after
lifting (post-lift), and four pre-plant treatments prior to planting in 2011.
Note: spp: p<0.001; trmt: p<0.05; spp x trmt: p<0.05

66

Figure A2.9. Mean root number of root growth potential-grown bareroot tree liners
subjected to four pre-plant treatments in 2011.
Note: spp: p<0.001; trmt: ns; trmt x spp: ns

67

Figure A2.10. Mean growth/dieback of container-grown bareroot tree liners subjected to
four pre-plant treatments in 2011.
Note: spp: p<0.001; trmt: p<0.05; spp x trmt: ns

68

Figure A2.11. Mean growth/dieback of field-grown bareroot tree liners subjected to four
pre-plant treatments in 2011.
Note: spp: p<0.05; trmt: ns; spp x trmt: ns

69

Figure A2.12. Mean growth/dieback of root growth potential-grown bareroot tree liners
subjected to four pre-plant treatments in 2011.
Note: spp: p<0.001; trmt: p<0.05; trmt x spp: p<0.05

70

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