American Chestnut Restoration
Acid rain and red spruce winter injury
of Red Spruce Winter Injury
Acid rain has
been broadly implicated in the deterioration of forest health,
especially the decline of red spruce forests in eastern North
America. We have documented that acid rain leaches calcium (Ca)
from foliage, depletes a physiologically important membrane Ca (mCa)
pool, destabilizes membranes, and significantly reduces the freezing
tolerance of red spruce foliage. These data support our hypothesis
that acid-induced reductions in cold tolerance are mediated through
mCa depletion. This is the only data-supported hypothesis of how
acid deposition increases freezing injury in red spruce. In
addition, because Ca serves as a chemical messenger of many
environmental stress signals across cell membranes, this hypothesis
may also provide a model for understanding how acid rain (and
possibly other contributors to environmental Ca depletion) could
broadly disrupt plant Ca nutrition and response to a variety of
secondary stresses (e.g., drought, salt, high or variable
temperatures, pathogens, etc.) in addition to freezing.
P.G., Schaberg, G.J. Hawley and G.R. Strimbeck. 1999. Acid rain
calcium nutrition and forest health. BioScience 49:789-800.
and D.H. DeHayes. 2000. Physiological and Environmental Causes of
Freezing Injury in Red Spruce. 2000. Chapter 6 in the Book:
Responses of Northern U.S. Forests to Environmental Change. Eds: R.
Mickler, R. Birdsey, and J. Hom. Springer-Verlag Ecological Studies
Series 139, pp 181-227.
D.H. DeHayes, G.J. Hawley, G.R. Strimbeck, J.R. Cumming, P.F.
Murakami, and C.H. Borer. 2000. Acid mist, soil Ca and Al alter the
mineral nutrition and physiology of red spruce. Tree
P.G. Schaberg and G.R. Strimbeck. 2001. Red spruce cold hardiness
and freezing injury susceptibility. Chapter 18. In: Conifer
Cold Hardiness. F. Bigras Ed. Kluwer Academic Publishers, Dordrecht,
the Netherlands, pp 495-529.
late winter in 2003 winter injury to the current-year foliage of red
spruce in Vermont was unusually abundant and widespread. To assess
the severity and extent of this damage, we measured foliar winter
injury at 28 locations in Vermont and surrounding states, and bud
mortality at a subset of these sites. Results of this extensive
survey revealed that 96% of all trees assessed showed some winter
injury, and trees lost an average of 46% of all current-year
foliage. An average of 32% of buds formed in 2002 were killed in
association with winter injury. Both foliar and bud mortality
increased with elevation and with crown dominance, and bud mortality
increased with greater foliar injury. Because heavy foliar
and bud losses can severely disrupt the carbon economies of trees,
the 2003 winter injury event could lead to further spruce decline
and mortality, particularly among dominant trees at higher
Schaberg, P.G., DeHayes, D.H., Hawley, G.J. 2004. Severe red spruce
winter injury in 2003 creates unusual ecological event in the
northeastern United States. Canadian Journal of Forest Research.
P.G. Schaberg, G.J. Hawley, and D.H. DeHayes. 2006.
Landscape-scale spatial patterns of winter injury to red spruce
foliage in a year of heavy region-wide injury. Can. J. For. Res.
P.G. Schaberg, D.H. DeHayes, J.B. Shane and G.J. Hawley. 1995.
Midwinter dehardening of montane red spruce during a natural thaw.
Can. J. For. Res. 25:2040-2044.
J.B. Shane, G.J. Hawley, G.R. Strimbeck, D.H. DeHayes, P.F. Cali and
J.R. Donnelly. 1996. Physiological changes in red spruce seedlings
during a simulated winter thaw. Tree Physiology. 16:567-574.
P.G. Schaberg, G.J. Hawley, C.H. Borer, J.R. Cumming and G.R.
Strimbeck. 1997. Physiological implications of seasonal variation in
membrane-associated calcium (mCa) in red spruce mesophyll cells.
Tree Physiology. 17:687-695.
Borer, C.H., D.H.
DeHayes, P.G. Schaberg and J.R. Cumming. 1997. Relative
quantification of membrane-associated calcium (mCa) in red spruce
mesophyll cells. Trees. 12:21-26.
G.R. Strimbeck, G.J. Hawley, D.H. DeHayes, J.B. Shane, P.F.
Murakami, T.D. Perkins and B.L. Wong. 2000. Cold tolerance and
photosystem function in a montane red spruce population:
physiological relationships with foliar carbohydrates. Journal of
Sustainable Forestry 10:173-180.
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New research on
the broader significance of Ca depletion indicates that the
same disruptions documented for red spruce can occur for other tree
species (e.g., eastern hemlock, balsam fir, and white pine), and
that soil-based Ca manipulation can also alter critical mCa pools.
Considering the unique role Ca plays in the physiological response
of cells to environmental stress, we propose that depletion of
biological Ca would impair basic stress recognition and response
systems, and predispose plants to exaggerated injury following
exposure to other environmental stresses. Diminished stress
response would be particularly problematic now because numerous
human activities (e.g., pollution production, ozone depletion,
climate change, the spread of exotic pests and pathogens, etc.) are
simultaneously subjecting forests to an increasing level and
diversity of stresses. Our ongoing work is examining the potential
risk of environmental Ca depletion on forest health through a
combination of controlled experiments and field surveys. The
potential contribution of Ca depletion to sugar maple decline is a
focus of our current work.
D.H. DeHayes, G.J. Hawley. 2001. Anthropogenic calcium depletion: a
unique threat to forest ecosystem health? Ecosystem Health,
Borer, C.H., P.G.
Schaberg, D.H. DeHayes, G.J. Hawley. 2001. Physiological implications of anthropogenic environmental calcium depletion. In:
The Tree 2000. Isabelle Quentin Ed. IQ Press, Montreal, pp 295-300.
Borer, C.H., Schaberg, P.G. DeHayes, D.H.
Hawley, G.J. 2004. Accretion, partitioning and sequestration of
calcium and aluminum in red spruce foliage: implications for tree
health. Tree Physiology. 24:929-939.
Borer, C.H., Schaberg P.G., D.H. DeHayes.
2005. Acidic mist reduces foliar membrane-associated calcium and
impairs stomatal responsiveness in red spruce. Tree Physiology.
J.W. Tilley, G.J. Hawley, D.H. DeHayes, and S.W. Bailey. 2006.
Associations of calcium and aluminum with the growth and health of
sugar maple trees in Vermont. Forest Ecology and Management
There is growing evidence that various
anthropogenic factors (e.g., high acid loading, nitrogen saturation,
forest harvesting, changing climatic conditions, soil aluminum (Al)
mobilization, and declines in atmospheric base cation deposition)
may be responsible for the depletion of Ca from forest ecosystems.
Because Ca is a biologically essential element, anthropogenic
alterations of this cation may have serious forest health
implications. In particular, because Ca plays an important role in
plant defense systems, Ca deficiency could result in inadequate
stress response and predispose trees to decline following exposure
to even normal stresses including drought, insects, pathogens, and
wounding. Our research examines if Ca deficiencies could limit the
ability of sugar maple (Acer saccharum Marsh.) trees to respond to
wounding. We wounded forest-grown sugar maple trees in a long-term,
replicated Ca manipulation study at the Hubbard Brook Experimental
Forest in New Hampshire, in which plots received applications of Ca
(to boost Ca availability above depleted ambient levels) or Al (to
compete with Ca uptake and further reduce Ca availability). We found
significantly (P<0.05) greater membrane-associated Ca and total
foliar Ca on plots fertilized with Ca in comparison with the Al
addition or control plots. By assessing the relative influence of Ca
manipulation treatments on specific Ca-dependent wound responses
(e.g., the accumulation of lignin, callose, and suberin) as well as
the rate of wound closure, the influence of Ca depletion on wound
response physiology is being tested. This study is a further
examination of the hypothesis that Ca-depletion suppresses stress
response systems and predisposes trees to decline.
additions of nitrogen (N) can lead to N-saturation (the accumulation
of N in excess of plant and microbial demands). Numerous published
reports have linked N-saturation with forest decline in regions
high N inputs, and suggest that decline is associated with N-induced
imbalances in other nutrients (especially Ca, Al, and Mg). However,
the physiological mechanisms through which nutrient imbalances may
cause decline have not been determined. Our survey of tree
physiology within montane plots receiving long-term N additions
showed that fertilization resulted in reductions of foliar Ca
concentrations to near-deficiency levels, and significantly
increased foliar respiration. N additions also increased foliar
winter injury. Our research assessed if N-induced disruptions in
physiology are mediated through reductions in mCa. This work showed
that the same mechanism of physiological disruption found for acid
rain impairment (significant reductions in mCa, membrane stability,
cold tolerance, and an increased rate of freezing injury) also
applies to chronic N additions. These findings suggest that N
additions can contribute to the same reduction of biological Ca
reserves that acid rain depletes.
T.D. Perkins and S.G. McNulty. 1997. Effects of chronic low-level N
additions on foliar elemental concentrations, morphology, and gas
exchange of mature montane red spruce. Can. J. For. Res.
S.T. Adams, G.T. Lawson, P.G. Schaberg and S.G. McNulty. 2000.
Long-term nitrogen fertilization increases winter injury in montane
red spruce foliage (Picea rubens) foliage. Journal of Sustainable
D.H. DeHayes, G.J. Hawley, P.F. Murakami, G.R. Strimbeck, S.G.
McNulty. 2002. Effects of chronic N fertilization on foliar
membranes, cold tolerance, and carbon storage in montane red
spruce. Canadian Journal of Forest Research. 32:1351-1359.
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is essential to the long-term health and survival of biological
populations because this diversity helps provide the adaptive
capacity needed to survive natural and manmade environmental
change. A loss of genetic diversity could be a serious threat to
the long-term health and productivity of forest ecosystems.
Silvicultural harvesting represents one anthropogenic force in which
sometimes large numbers of trees and the genes they contain are
removed from forest systems. However, the long-term impact of tree
removals on the genetic base and ecological resiliency of forests is
In one study we
examined the influence of long-term silvicultural treatment on the
genetic base of an eastern hemlock forest. This study showed that
protracted silvicultural selection altered the frequency of rare
alleles (unusual gene forms) in treated populations.
Silvicultural selection that preferentially removed larger and
better-formed trees reduced the presence of rare alleles compared to
the control, whereas silvicultural selection that preferentially
removed small and poorly formed trees increased the presence of rare
alleles relative to control.
DeHayes, D.H., G.L.,
Jacobson, P.G. Schaberg, B. Bongarten, L. Iverson, and A.C.
Diefenbacher-Krall. 2000. Forest responses to changing climate:
lessons from the past and uncertainty for the future. Chapter 14 in
the Book: Responses of Northern U.S. Forests to Environmental
Change. Eds: R. Mickler R. Birdsey, and J. Hom. Springer-Verlag
Ecological Studies Series 139, pp 495-540.
Hawley, G., D.H.
DeHayes, P.G. Schaberg, J. Brissette. 2006. Genetic effects of
diameter-limit cutting. In: Kenefic, Laura S., Nyland, Ralph D.
eds. Proceedings of the conference on diameter-limit cutting in
northeastern forests.; 2005 May 23-24; Amherst, MA. Gen. Tech. Rep.
NE-341. Newtown Square, PA: U.S. Forest Service: 41-42. Northeastern
Schaberg P.G., DeHayes, D.H., Brissette, J. 2005. Silviculture
alters the genetic structure of an eastern hemlock forest in Maine,
USA. Canadian Journal of Forest Research, 35:143-150.
established a unique second study: a genetically mapped white pine
forest that combines basic inventory data (e.g., the size, growth,
location of trees) with an assessment of tree genetics (isozyme
analysis) within a GIS database. This database was used to conduct
simulated harvests that “removed” individual trees based on
traditional management criteria (e.g., tree size, crown class, etc.)
and then calculated the consequence of tree removals on the genetics
of the residual stand. Because different simulation runs utilized
different removal criteria, we were able to compare the impact of
many varying management options on forest genetics without actually
cutting any trees. Results of initial simulated harvests indicated
that most management prescriptions had little impact on the genetics
of the residual stand. A noted exception was that some harvests
preferentially altered the frequency of rare alleles.
Schaberg, P.G., Hawley, G.J., DeHayes, D.H. 2005. Genetic
subpopulation structuring and its implications in a mature eastern
white pine stand. Canadian Journal of Forest Research, Can. J.
For. Res. 35:1041-1052.
Hawley, G.J., DeHayes, D.H., Nijensohn, S.E. 2004. Silvicultural
management and the manipulation of rare alleles. In
Silviculture and the Conservation of Genetic Resources for
Sustainable Forest Management. J. Beaulieu Ed. Natural Resources
Canada, Canadian Forest Service, Information Report LAU-X-128,
simulated harvests support findings from our field-based hemlock
study and suggest that rare alleles may be particularly prone to
manipulation through harvesting. In
addition to its unique research value, a genetically mapped forest
could be an important demonstration site at which forest managers
could literally visualize (on field-based computers) the impact of
management prescriptions (applied using simulated cuts) on a
parameter that they traditionally can’t evaluate: the forest’s
genetic base. Studies of the influence of silvicultural selection
on forest genetics will help assess if harvesting prescriptions have
the potential to enhance or diminish genetic diversity within
populations. This information could also help in the formulation of
silvicultural guidelines that protect or possibly increase
within-species genetic diversity.
Seasonal red coloration
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red, blue or purple pigments most often seen in flowers and fruits.
Although the biochemistry and physiology of chlorophylls, foliar
green pigments, are well understood, less is known about
anthocyanins and their role in leaves. Much of the research
conducted on this red
originates in the economical significance of controlling flower and
fruit color. And recently, its role in human health as an
antioxidant or scavenger of reactive oxygen species is currently
being studied as a possible cancer-defense mechanism. Is it
possible that anthocyanins could perform a similar function in
trees? Indeed, many factors are known to elicit anthocyanin
biosynthesis in foliage including UV-B radiation, osmotic stress,
drought, low temperature, nutrient deficiency, wounding, pathogen
infection and ozone exposure. Because formation of anthocyanins
requires energy, it is believed that they must be of some benefit to
tree health. In fact, recent work on woody species has emphasized
the potential value of anthocyanins as a “light screen” that
protects the photosynthetic apparatus of senescing leaves and
enables prolonged nutrient absorption before abscission. It is also
possible that anthocyanins may increase both cold hardiness and
specific function of anthocyanin and how it may relate to
overall tree and forest health is unclear. Our research team is
currently in the process of identifying the factors that stimulate
anthocyanin biosynthesis. We hope to gain a detailed understanding
of the linkage between stress exposure and anthocyanin production
which may provide insight into plant stress response
systems, and help assess the utility of leaf color analysis as an
indicator of stress.
Computer-based Leaf Color Analysis
As part of this
research, our research group developed a computer-based image
analysis technique for quantifying red leaf color without the use of
costly or complicated laboratory analyses.
M.R. Turner, A.K. van den Berg, and Paul Schaberg. 2006. An
instructional guide for leaf color analysis using digital imaging
software. Gen Tech. Rep. NE-327. Newtown Square, PA: U.S.
Department of Agriculture, Forest Service, Northeastern Research
Station. 33 p.
Coloration and Nitrogen/Carbohydrates
Initial work on
this topic examined the environmental and chemical factors range of parameters for mature sugar maple trees
throughout the growing season and autumn, only foliar nitrogen (N),
sugar and starch concentrations were significantly correlated with
red coloration. We hypothesize that
nutrient (particularly N) limitations in our trees provided the
biochemical triggers (low N and high sugar signals), energy, and
carbohydrate building blocks needed for the facultative production
of anthocyanins. Experimental manipulations are now being conducted
to test this hypothesis and other possible connections between
anthocyanin expression and stress response.
van den Berg, A.K.,
J.R. Donnelly, P.F. Murakami, P.G. Schaberg. 2001. Development of
fall foliage color in sugar maple. In: The Tree 2000.
Isabelle Quentin Ed. IQ Press, Montreal, pp 356-360.
A.K. van den Berg, P.F. Murakami, J.B. Shane, J.R. Donnelly. 2003.
Factors influencing red expression in the autumn foliage of sugar
maple trees. Tree Physiology. 23:325-333.
Fall Red Coloration
is focusing on spring coloration of leaves and the function of this
pigment may differ at this time of year compared to
Our preliminary findings suggest that, like our initial autumn
study, leaves with low N concentrations tend to exhibit more red.
In addition, it appears that spring red leaf coloration can occur in
many species (e.g., American beech and Eastern cottonwood) that
normally do not produce anthocyanins during autumn. Why would a
species manufacture anthocyanins in the spring but not the fall? Do
anthocyanins perform different functions during these times? Do
different environmental signals trigger red color development in the
spring versus the fall? Answers to these and other questions are
needed to decipher the ecological function and potential benefits of
To relate color
development and nutrient/carbohydrate concentration to abscission
layer formation we collected petioles of green, yellow and red
leaves and measured abscission layer length. We also determined the
strength of the abscission layer by adding weights to each leaf and
recording the weight necessary to detach individual leaves from
branches. Nutrient and carbohydrate analyses were also performed.
Abscission layers in petioles of yellow leaves were more completely
formed than those of green and red leaves. Yellow leaves were also
more easily detached from branches, followed by red and then green
leaves. Leaves are now being processed for N content. Preliminary
data indicate a negative relationship between N and red coloration:
less N, more red.
We have begun
exciting new research studying the role of anthocyanins and other
plant antioxidants in protecting leaves from dangerous forms of
oxygen called reactive oxygen species (ROS). ROS occur when a plant
is under stress and can quickly damage foliar tissue if not
eliminated. Anthocyanins may be one of several plant compounds that
eliminate this toxic oxygen and prevent significant foliar damage.
Our research team is developing laboratory methods to measure
antioxidant enzyme activity. With this new application we hope to
better define the role of anthocyanins in plant stress response
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Yellow-cedar in Alaska
an economically and ecologically important species that has
experienced a dramatic decline in southeastern Alaska during the
past 100 years. Extensive research has shown that this decline has
no likely biotic cause, but suggests that one or more abiotic
factors (particularly climatic warming) may have instigated
decline. To evaluate the possibility that inadequate cold hardiness
is a contributor to this decline, scientists from the Pacific
Northwest Station and our research team measured the foliar freezing
tolerance of yellow-cedar trees in declining and non-declining
stands. Foliar freezing tolerance of western hemlock, a sympatric
species not experiencing
mortality, was measured for comparison. Freezing tolerance was
assessed in the fall, winter and spring to determine if seasonal
differences in hardiness help explain species-specific injury. Two
results consistent with field reports of yellow-cedar decline were
found: 1) because yellow-cedar trees experienced greater vernal
dehardening, yellow-cedar trees were uniquely vulnerable to spring
freezing injury, and 2) stands below 130 m appeared more vulnerable
to freezing injury than stands above 130 m. These results support
the possibility that limited foliar cold hardiness during spring
contributes to the decline of yellow-cedar trees at low elevations. However, we are now evaluating whether root
freezing tolerance may be more directly pertinent to decline in the
P.E. Hennon, D.V. D'Amore, G.J. Hawley, and C.H. Borer. 2005.
Seasonal differences in freezing tolerance of yellow-cedar and
western hemlock trees at a site affected by yellow-cedar decline.
Can. J. For. Res. 35:2065-2070.
relations of evergreen conifers during winter have been studied
little despite their potential importance to understanding yearly
energy budgets and plant adaptations to the cold. Red spruce and
other evergreens retain their foliage throughout the winter, thus
they have the potential for year-round carbon assimilation. Field
measurements of photosynthesis have shown that winter carbon
assimilation can be significant in regions where winter climates are
mild. However, studies in colder areas have been limited and
inconsistent in their portrayal of photosynthetic ability during
winter. In fact, the most prevalent data documents disruptions of
the photosynthetic machinery within cells that would limit winter
carbon capture. Although questions concerning winter carbon exchange
exist for all northern conifers, information about the
photosynthetic activity of red spruce is of particular interest.
Since the 1960’s, growth rates of red spruce in New England and New
York have measurably declined. Freezing injury and the associated
loss of needles have been identified as a major contributor to this
decline. Understanding the physiological activity of red spruce
needles during winter would improve scientific understanding of this
species’ ecological niche, and help assess potential mechanisms of
red spruce decline.
evaluate the winter physiology of red spruce, I studied the winter
carbon relations of red spruce. My research documented that red
spruce have rates of net photosynthesis close to zero for much of
the winter, but that photosynthetic rates more than tripled during
protracted thaws, with rates for some trees approximated growing
season levels. Additional work verified that
increases in field photosynthesis can occur within four days of thaw
inception, whereas increases in photosynthetic
capacity (maximum photosynthetic rates measured under near-optimal,
controlled growing conditions) can occur within 48h (natural thaw)
or even 3h (simulated thaw). Winter photosynthesis
could benefit leaves by augmenting energy stores when more distal
carbon reserves are less available due to cold-induced reductions in
phloem transport. Increased sugar concentrations could also help
foliage maintain cold tolerance levels needed to avoid freezing
R.C. Wilkinson, J.B. Shane, J.R. Donnelly, and P.F. Cali. 1995.
Winter photosynthesis of red spruce from three Vermont seed
sources. Tree Physiology. 15:345-350.
J.B. Shane, J.R. Donnelly, P.F. Cali, and G.R. Strimbeck. 1998.
Photosynthetic capacity of red spruce during winter. Tree
M.C. Snyder, J.B. Shane, and J.R. Donnelly. 2000. Seasonal
patterns of carbohydrate reserves in red spruce seedlings. Tree
American Chestnut Restoration
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chestnut is a tree species of unique ecologic and economic value
that was virtually eliminated following a blight caused by the
fungal pathogen, Cryphonectria parasitica (Murr.) Barr, that
was accidentally introduced in New York City in 1904. In order
to restore this valuable
species, multiple approaches to decrease the virulence of the
pathogen or increase the resistance of the tree have been evaluated.
However, only one technique - producing highly resistant trees via
the hybridization of American and Chinese chestnuts with backcrosses
to American chestnut - shows promise for near-term restoration.
The American Chestnut Foundation (TACF) is leading this
hybridization/backcrossing effort. Our research team, in
collaboration with TACF scientists, has initiated new research to
support the restoration of American chestnut in Vermont and
elsewhere in the Northern Forest. We are currently evaluating
the role that inadequate cold hardiness may play in limiting the
success of the species at its northern limit. In addition, we
are providing hybrid/backcrossed chestnut with germplasm from
Vermont-adapted American chestnut, and testing techniques for
cultivating American chestnut under Vermont conditions.
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