DENDROCHRONOLOGY, HISTORICAL ECOLOGY AND IMPACTS OF GLOBAL CHANGE ON FORESTS IN THE EASTERN UNITED STATES.

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: TERMINATED
• Funding Source: MCINTIRE-STENNIS
• Reporting Frequency: Annual
• Accession No.: 0213549
• Project No.: PEN04240
• Project Start Date: Jul 1, 2008
• Project End Date: Jun 30, 2013

Project Director
Abrams, MA.

Recipient Organization
PENNSYLVANIA STATE UNIVERSITY
208 MUELLER LABORATORY
UNIVERSITY PARK,PA 16802

Performing Department
Ecosystem Science & Management

Non Technical Summary
JUSTIFICATION: The magnitude of anthropogenic impacts on North American forests increased dramatically following European settlement (Whitney 1994). Global change phenomenon, such as increased atmospheric CO2, precipitation and nitrogen inputs to ecosystems, as well as changing land-use and disturbance regimes, are having very pronounced effects on forests worldwide (Bazzaz 1990). Studies have shown increased radial growth in response to global change factors such as nitrogen fertilization and increased CO2 levels (Aber et al. 1989). These potential enrichment factors may cause growth increases even in very old trees (Abrams and Orwig 1995). Large increases in radial growth have also been caused by stand-wide disturbances that produced environmental conditions suitable for both the release of trees left on sites, and the rapid establishment of regeneration (Abrams and Nowacki 1992, Abrams et al. 2001, Abrams 2003). These global climate and land-use changes have significantly impacted the growth and structure of forests in the eastern United States within the last 50 to 100 years. In addition to climate change, the magnitude of anthropogenic disturbances in North American forests changed dramatically following European settlement, including extensive clearcutting of forests followed by large-scale wildfire, land conversion to agriculture, fire suppression starting in the early 1920's, and the introduction of exotic insects and diseases (e.g., the chestnut blight). All of these have led to unprecedented and rapid changes in forest composition and age structure, particularly in the eastern United States (Keever 1953, Abrams and Nowacki 1992, Whitney 1996). Anthropogenic impacts during the late 19th and early 20th centuries were tantamount to a perfect storm for most forests in the eastern U.S. This period represented both the height and the tail end of the clearcutting era and the catastrophic wildfires that followed, the start of the Smoky the Bear era of fire suppression, and the beginning and peak of the chestnut blight (Whitney 1994). This era preceded the major invasion of later successional species in oak forest understories and the rise in deer populations that have decimated oak regeneration in many areas. Although a suite of factors, such as climate change, logging, animal and insect grazing, and disease, have affected the dominance of oak, the influence of fire in the eastern deciduous biome is probably most important. Fire, whether it has occurred to a low, moderate, or high degree, seems to be the common denominator for the development of oak forests on upland sites and their past and present ecological status. I propose using dendroecology, community ecology, and ecophysiology to further study historical development of forests in the eastern United States in relation to natural and anthropogenic factors, including global change processes.

Animal Health Component

0%

Research Effort Categories

Basic

(N/A)

Applied

(N/A)

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
123	0613	1070	100%

Knowledge Area
123 - Management and Sustainability of Forest Resources;

Subject Of Investigation
0613 - Mixed conifer-broadleaf forests;

Field Of Science
1070 - Ecology;

Keywords

tree rings

disturbance

fire

succession

dendrochronology

global change

Goals / Objectives
To examine the dendrochronology, community ecology, and historical development of mixed-oak and conifer dominated forests in the mid-Atlantic region. More specifically: 1. Compare the composition of forests in the mid-Atlantic region prior to European settlement in the 1700s with present-day forest composition. 2. Conduct a detailed analysis of the age structure and radial-growth dynamics (using tree rings) in a variety of mature and old-growth forests to access long-term stand dynamics and climatic variation in relation to ecological history and global change phenomenon. 3. Evaluate the fire history and impacts of fire on tree regeneration in hardwood and conifer forests in the northeast and mid-Atlantic regions. 4.Contrast gas exchange, leaf morphology, and seedling growth in a mixed-oak forest understory warmed by artificial heating. I believe that a future vision of ecosystem management in the mid-Atlantic region depends on an understanding of the ecological history of disturbance, land-use, and global change and their role in the evolution of regional forests. I hope that the results of this research will contribute to that vision and the long-term health and fitness of our forests.

Project Methods
1. By comparing the presettlement forest data summarized from the warrant maps one can assess some of the major compositional changes that has occurred in regional forests. 2. Mature and old-growth hardwood and conifer forests in the mid-Atlantic region will be used for dendroecological study. In each forest 60-70 trees across all species and diameter classes will be cored using increment bores. Age determinations for all cores will be made using a dissecting microscope. Cores from the oldest trees will be used to construct a growth chronology of the site spanning 200-400 years. These cores will be dried, mounted and sanded. Annual-growth increments will be measured to the nearest 0.01 mm with a tree-ring measuring device (Regents Instruments Inc., Quebec, Canada) and recorded using the MACDENDRO microcomputer program. After cross-dating using signature years, annual increments will be averaged to obtain a mean growth chronology for the one or two dominant tree species. A ring-width index will also be created for each tree chronology by dividing yearly mean measured growth values by the expected values obtained from linear regression (Fritts and Swetnam 1989). 3. All tree cookies and increment cores from selected study areas will be dried, mounted, and sanded with increasingly finer sand paper. The samples will be examined for signature years for crossdating purposes to help identify missing, partial, or false rings (Stokes and Smiley 1996). 4. Physiological measurements was conducted during the growing season in understory plots receiving warming from heat lamps. Between five and seven study plants per species (red oak, chestnut oak, hickory (Carya), and red maple) per subplot will be evaluated. Pre-dawn water potentials will be estimated in one leaf per tree using a pressure chamber (Model 1000, PMS Instruments Co., Corvallis OR) at 0600 hours solar time. At mid-day (1100-1300 hours solar time) gas exchange measurements will be conducted on two fully expanded leaves. A portable photosynthesis unit (LCA-3, ADC Ltd, Herts, UK) will be used to estimate net photosynthesis (A), leaf conductance to water vapor diffusion (gwv), leaf temperature (T leaf) and photosynthetic photon flux density (PPFD) for each leaf.

Progress 07/01/08 to 06/30/13

Outputs
Target Audience: Forest ecologist, forest managers, natural resources professionals, academic scientists. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? Mature and old-growth forests in the mid-Atlantic and central Appalachian regions were the focus for ecological and global change impact studies. The main drivers of global change are climate change and human land use. We addressed these issues by studying the impacts of climate, forest harvesting, forest conservation, invasive species, and fire on forest structure and dynamics. The timing and composition of forest regeneration was reconstructed across elevation gradients in the central Appalachians to tease out the influence of climate and biotic interactions on forest community development. Unique late-successional (120+) forests in Pennsylvania were identified and measured to assess their structural diversity compared to the pervasive 80-110 year-old-forests that dominate the state's woods. These unique late-successional forests provide valued wildlife habitat and baseline information for active forest management intended to simulate mature-forest attributes. Global change impacts on forest dynamics were further studied with a project to measure the impacts of a diverse community of non-native shrub communities on forest dynamics. We must recognize that past, current, and future land-use history has all play important roles in the structure and function of forest trees. Environmental scientists need to take a much longer view of climate change and land-use history impacts when they assess the current condition of forests How have the results been disseminated to communities of interest? Yes via scientific publications, talks at professional meetings and undergraduate and graduate student training What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Forest community composition and dynamics are the product of disturbance history (natural and human caused), climate influences on tree physiology and regeneration, and biotic interactions among species. These multi-scale, interacting factors challenge our ability to predict eastern forest response to global change. However, our long-term and multi-factor field research provides empirical information needed to improve predictive models. For example, when fire is suppressed in oak forests during the 20th century, they are rapidly replaced by later successional, fire sensitive species, such as maple, beech, birch, and black gum. Near urban areas, forest succession following human and natural disturbance is being further complicated by the invasion of forest understory by a diverse community of non-native shrubs. These shrubs reduce light availability in the forest understory, selecting for tree species that are highly shade tolerant. Forest regeneration responds to warmer temperature by advancing the growing season of tree species by 1 week per 1OC warming. However, biotic interactions among plants and microbial communities temper the influence of simulated warming, demonstrating their important role in ecosystem dynamics. Throughout the eastern U.S., interactions and feedback among climate, vegetation, soils and topography, large- and small-scale disturbances, anthropogenic factors, and wildlife impacts created an ecological dynamic that can best be understood through empirical field studies of observational long-term, experimental, and multifactor perspectives.

Publications

• Type: Journal Articles Status: Published Year Published: 2013 Citation: Abrams, M. D. and M. Scheibel. 2013. A five-year record mast production and climate in contrasting mixed-oak-hickory forests on the Mashomack Preserve, Long Island, New York. Natural Areas Journal 33: 99-104.
• Type: Journal Articles Status: Published Year Published: 2008 Citation: Abrams, M. D. and G. J. Nowacki. 2008b. Native Americans as active and passive promoters of mast and fruit trees in the eastern USA. The Holocene 18: 1123-1137.
• Type: Journal Articles Status: Published Year Published: 2013 Citation: McDaniel, M.D., J.P. Kaye, and M.W. Kaye, 2013. Increased temperature and precipitation had limited effects on soil extracellular enzyme activities in a post-harvest forest. Soil Biology and Biochemistry 56: 90-98.
• Type: Book Chapters Status: Published Year Published: 2013 Citation: McDaniel, M.D. R.J. Wagner, C.R. Rollinson, B.A. Kimball, M.W. Kaye, and J.P. Kaye, 2013. Microclimate and ecological threshold responses from a warming and wetting experiment following whole-tree harvest in central Pennsylvania. Theoretical and Applied Climatology 113: online first DOI 10.1007/s00704-013-0942-9.

Progress 10/01/11 to 09/30/12

Outputs
OUTPUTS: Mature and old-growth forests in the mid-Atlantic and central Appalachian regions were the focus for ecological and global change impact studies. The main drivers of global change are climate change and human land use. We addressed these issues by studying the impacts of climate, forest harvesting, forest conservation, invasive species, and fire on forest structure and dynamics. The timing and composition of forest regeneration was reconstructed across elevation gradients in the central Appalachians to tease out the influence of climate and biotic interactions on forest community development. Unique late-successional (120+) forests in Pennsylvania were identified and measured to assess their structural diversity compared to the pervasive 80-110 year-old-forests that dominate the state's woods. These unique late-successional forests provide valued wildlife habitat and baseline information for active forest management intended to simulate mature-forest attributes. Global change impacts on forest dynamics were further studied with a project to measure the impacts of a diverse community of non-native shrub communities on forest dynamics. We must recognize that past, current, and future land-use history has all play important roles in the structure and function of forest trees. Environmental scientists need to take a much longer view of climate change and land-use history impacts when they assess the current condition of forests. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Global change ecologists, forest managers, ecological modelers PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
Forest community composition and dynamics are the product of disturbance history (natural and human caused), climate influences on tree physiology and regeneration, and biotic interactions among species. These multi-scale, interacting factors challenge our ability to predict eastern forest response to global change. However, our long-term and multi-factor field research provides empirical information needed to improve predictive models. For example, when fire is suppressed in oak forests during the 20th century, they are rapidly replaced by later successional, fire sensitive species, such as maple, beech, birch, and black gum. Near urban areas, forest succession following human and natural disturbance is being further complicated by the invasion of forest understory by a diverse community of non-native shrubs. These shrubs reduce light availability in the forest understory, selecting for tree species that are highly shade tolerant. Forest regeneration responds to warmer temperature by advancing the growing season of tree species by 1 week per 1OC warming. However, biotic interactions among plants and microbial communities temper the influence of simulated warming, demonstrating their important role in ecosystem dynamics. Throughout the eastern U.S., interactions and feedback among climate, vegetation, soils and topography, large- and small-scale disturbances, anthropogenic factors, and wildlife impacts created an ecological dynamic that can best be understood through empirical field studies of observational long-term, experimental, and multifactor perspectives.

Publications

• Rollinson, C., M. Kaye, and L. Leites, 2012. Community assembly and plant cover responses to experimental warming and increased precipitation of an early successional forest. Ecosphere (Accepted for Publication).
• Wagner, R. J., M. W. Kaye, M. D. Abrams, P. J. Hanson, and M. Martion. 2012. Tree-ring growth and wood chemistry response to manipulated precipitation variation for two temperate Quercus Species. Tree-Ring Res. 68:17-29.
• Abrams, M. D. and S. E. Johnson. 2012. Long-term impacts of deer exclosures and land-use history on forest composition at the Valley Forge National Historical Park, Pennsylvania. J. of the Torr. Bot. Soc. 139:167-180.
• Fletcher, C., M. Abrams et al. 2012. Climate change impacts on the Pasoh tropical rainforest. Perlium Press. Kuala Lumpur, Malaysia. 73 pages.
• Rollinson, C. R. and M. W. Kaye. 2012. Experimental warming alters phenology of certain plant functional groups in an early-successional forest community. Global Change Bio. 18:1108-1116.

Progress 10/01/10 to 09/30/11

Outputs
OUTPUTS: Mature and old-growth hardwood and conifer forests in the mid-Atlantic region were used for ecological and climate change impact studies. In each forest, 60-70 trees across all species and diameter classes were recorded for size and age. The composition of forest regeneration is similarly affected by climate variability. Experimental and observational approaches were used to quantify how tree species in eastern deciduous forests have responded and will continue to respond to climate warming. Species interactions such as competition for light and space are altered by climate change and will have cascading effects on future forest composition. It is predicted that the continued increase in global greenhouse gases and climate warming will have far-reaching and often negative implications for the environment and conservation biology. Many forest tree responses (photosynthesis and growth) have actually been stimulated by climate change, particularly in temperate environments. Environmental scientists need to understand the natural range of variation in climate and its role in present and future changes, not only anthropogenic forcing. Natural climate forcing is more difficult to predict, can be abrupt, and therefore more difficult to model. Over the last century, the forest macro- and micro-environment has changed dramatically in most parts of the world, including the impacts of land-use history. Old-growth forests have been logged and converted to pasture, farmland or young, fast-growing, forests. The growing season has been extended by about 10-20 days in temperate regions. Precipitation chemistry has become more acidic but richer in nitrogen from the burning of fossil fuels. We must recognize that past land-use history has and will continue to play a very important role in the structure and function of forest trees. Environmental scientists need to take a much longer view of climate change and land-use history impacts when they assess the current condition of global forests. PARTICIPANTS: Sara Johnson, Rebekah Wagner, and Christy Rollinson TARGET AUDIENCES: Global ecologists, forest mangers, ecological modelers PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
When fire is suppressed in oak forests during the 20th century, they are rapidly invaded by later successional, fire sensitive species, such as maple (Acer), beech (Fagus), birch (Betula), and black gum (Nyssa). These species are now replacing oak and becoming dominant trees. We believe that the suppression of fire and the successional replacement of oak forests is a cause and effect relationship. My studies specifically address the fire and oak hypothesis, long-term burning studies in oak forests, and the direct dating of fire scars in old-growth oak forests to resolve some of the remaining issues about the ecological role of fire in the development of oak forests. Moreover, fire is not the only factor that has influenced the ecology of oak forests during the 20th century. The impacts of acid rain, elevated CO2, potential global warming, herbivory, and gypsy moth outbreaks were studied in relation to the decline in oak recruitment and increase in later successional tree species in eastern oak forest. Throughout the eastern U.S., interactions and feedback among climate, vegetation, soils and topography, large- and small-scale disturbances, anthropogenic factors, and wildlife impacts created an ecological dynamic for oak forests that can only be understood from a long-term, multifactor perspective. In relation to global change, most trees studied in the eastern U.S. are exhibiting increase growth (in terms of basal area increment) over the last 50 years.

Publications

• Abrams, M. D. 2011. Adaptations of Forest Ecosystems to Air Pollution and Climate Change. Tree Physiology 31:258-261.
• Kaye, W. W. 2011. Mesoscale synchrony of aspen establishment across the interior western US. Forest Ecology and Management 26:389-397.
• Sands, B. A. and M. D. Abrams. 2011. A 184-year history of fire and recent fire suppression impacts in pine and oak forests of Menominee County, Wisconsin USA. American Midland Naturalist 166:325-338.

Progress 10/01/09 to 09/30/10

Outputs
OUTPUTS: Physiological measurements were conducted during the 2010 growing season in understory plots receiving warming from heat lamps. Between five and seven study plants per species (red oak, chestnut oak, hickory (Carya), and red maple) per subplot were evaluated. Pre-dawn water potentials were estimated in one leaf per tree using a pressure chamber (Model 1000, PMS Instruments Co., Corvallis OR) at 0600 hours solar time. At mid-day (1100-1300 hours solar time) gas exchange measurements will be conducted on two fully expanded leaves. A portable photosynthesis unit (LCA-3, ADC Ltd, Herts, UK) was used to estimate net photosynthesis (A), leaf conductance to water vapor diffusion (gwv), leaf temperature (T leaf) and photosynthetic photon flux density (PPFD) for each leaf. Immediately following gas exchange measurements each leaf was harvested for water potential measurements, and processed for chemical and morph-ological analysis. Gravimetric soil moisture measurements were taken at 20 cm depth and soil nitrogen content measured at the Penn State Agricultural Analysis Center. Morphological measurements were made on leaves harvested for water potential measurements (two leaves per tree). Leaf area was measured using a leaf area meter (Li-Cor, Lincoln, NE) and the leaves were dried in a drying oven. Specific leaf mass will be calculated by dividing total leaf area (excluding petiole) by dry leaf weight. An early successional forest community was monitored under experimental warming and watering treatments to identify responses to predicted changes in climate. Phenology and percent cover were monitored bi-weekly through the growing season and biomass was measured at the end of the growing season. An experiment was initiated to measure the effects of non-native shrub communities on the leaf litter dynamics in a mature, mixed-hardwood forest in central Pennsylvania. Leaf litter was collected weekly in Fall 2010. Leaf quality was measured by analyzing percent carbon and nitrogen in leaf letter for native and invasive species. PARTICIPANTS: Sarah Johnson, Rebekah Wagner, Christy Rollinson TARGET AUDIENCES: Forest fire managers and experts evaluating the impact of global change on eastern forests. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
When fire is suppressed in oak forests during the 20th century, they are rapidly invaded by later successional, fire sensitive species, such as maple (Acer), beech (Fagus), birch (Betula), and black gum (Nyssa). These species are now replacing oak and becoming dominant trees. We believe that the suppression of fire and the successional replacement of oak forests is a cause and effect relationship. Nonetheless, additional studies specifically addressing the fire and oak hypothesis, long-term burning studies in oak forests, and the direct dating of fire scars in old-growth oak forests are needed to resolve some of the remaining issues about the ecological role of fire in the development of oak forests. Moreover, fire is not the only factor that has influenced the ecology of oak forests during the 20th century. The impacts of acid rain, elevated CO2, potential global warming, herbivory, and gypsy moth outbreaks need to be studied in relation to the decline in oak recruitment and increase in later successional tree species in eastern oak forest. Throughout the eastern U.S., interactions and feedback among climate, vegetation, soils and topography, large- and small-scale disturbances, anthropogenic factors, and wildlife impacts created an ecological dynamic for oak forests that can only be understood from a long-term, multifactor perspective. The simulated climate change experiment showed that tree seedling germination advances under warmer conditions, the composition of regenerating species is influenced by warming, and woody species are more sensitive to simulated climate change than herbaceous species. The experiment is still underway and additional seedling physiology, soil biogeochemistry, and plant carbon allocation will be measured. We found that leaf litter of invasive species has higher nitrogen concentrations than native species, implying a long-term impact on nitrogen cycling in invaded forests. Additionally, we found that native species drop their leaves later in the season than natives and they reduce the amount of light reaching the forest floor by half. These results imply that understory invasion by non-native shrubs can impact both forest community structure and ecosystem dynamics.

Publications

• Abrams, M. D. 2010. Native Americans, Smoky Bear and the rise and fall of eastern oak forests. Penn State Environmental Law Review 18(2):141-154.
• Kaye, M. W., S. T. Jackson, and C. A. Woodhouse. 2010. Persistence and expansion of ponderoda pine woodlands in the west-central Great Plains during the past two centuries. Journal of Biogeography 37:1668-1683.
• Abrams, M. D. 2010. Impacts of land-use history and climate change on vegetation biodiversity in North America and Asia. Asia Pacific Mountain Network Bulletin Volume 15(6):4 pgs.
• Abrams, M. D. and B. A. Sands. 2010. Oak forest composition on contrasting soil types at the Mohonk Preserve, eastern New York. Northern Journal of Applied Forestry 27:105-109.

Progress 10/01/08 to 09/30/09

Outputs
OUTPUTS: Physiological measurements were collected during the 2009 growing season in 16 research plots within a field experiment simulating predicted increases in temperature and precipitation. Between 1-2 study plants per species (northern red oak, chestnut oak, black oak, post oak, white oak, red maple, sweetgum, black birch, and black cherry) per plot were evaluated for seed germination and seedling growth. Pre-dawn water potentials were estimated in one leaf per tree using a pressure chamber (Model 1000, PMS Instruments Co., Corvallis OR) at 0600 hours solar time. At mid-day (1100-1300 hours solar time) gas exchange measurements were conducted on three fully expanded leaves. A portable photosynthesis unit (LCA-3, ADC Ltd, Herts, UK) was used to estimate net photosynthesis (A), leaf conductance to water vapor diffusion (gwv), leaf temperature (T leaf) and photosynthetic photon flux density (PPFD) for each leaf. Immediately following gas exchange measurements leaves were harvested for water potential measurements, and then dried and processed for foliar nutrient concentrations analysis. Near the end of the growing season tree seedling leaf area was measured using a leaf area meter (Li-Cor, Lincoln, NE) and the leaves were dried in a drying oven. Specific leaf mass will be calculated by dividing total leaf area (excluding petiole) by dry leaf weight. Soil temperature and moisture to 5 com depth are continually monitored with buried probes and soil nutrient availability measured with in situ ion-exchange resins. Preliminary research was presented at the 17th Penn State Plant Biology Symposium in State College, PA and at the 2009 annual meeting of the Ecological Society of America in Albuquerque, NM. PARTICIPANTS: Marc Abrams and Margot Kaye TARGET AUDIENCES: Scientists, Academics, State and Federal Agencies and land managers and private land owners involved with natural resource issues, including the PA DCNR and federal DOD, DOE, NPS, Forest Service and BIA. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
When fire is suppressed in oak forests during the 20th century, they are rapidly invaded by later successional, fire sensitive species, such as maple (Acer), beech (Fagus), birch (Betula), and black gum (Nyssa). These species are now replacing oak and becoming dominant trees. The suppression of fire and the successional replacement of oak forests is a cause and effect relationship. Nonetheless, additional studies specifically addressing the fire and oak hypothesis, long-term burning studies in oak forests, and the direct dating of fire scars in old-growth oak forests are needed to resolve some of the remaining issues about the ecological role of fire in the development of oak forests. Moreover, fire is not the only factor that has influenced the ecology of oak forests during the 20th century. The impacts of acid rain, elevated CO2, herbivory, gypsy moth outbreaks, and climate change need to be studied in relation to the decline in oak recruitment and increase in later successional tree species in eastern oak forest. Models correlating climate change with future forest composition predict major changes in forest species composition in the eastern United States over the next century. These predictions are based on correlative models linking predicted changes in climate with species distribution maps. Little empirical evidence exists to support or refute the model predictions. Our experiment approach to studying the response of eastern tree species to simulated climate change can test model predictions, and furthermore, provide mechanistic explanations as to why particular tree species will be winner or losers with predicted changes in climate. Throughout the eastern U.S., interactions and feedback among climate, vegetation, soils and topography, large- and small-scale disturbances, anthropogenic factors, and wildlife impacts created an ecological dynamic for oak forests that can only be understood by combining long-term, multifactor perspectives with mechanistic experimental studies.

Publications

• Black, B.A., M.D. Abrams, P. Gould, and J. Rentch. 2009. Properties of boundary-line release criteria in North American tree species. Annals of Forest Science 66. 19 pp. http://dx.doi.org/10.1051/forest/2008087.
• Johnson, S. and M.D. Abrams. 2009. Basal area increment trends across age classes for two long-lived species in the eastern U.S. Kaczka R, Malik I, Owczarek P, Gartner H, Helle G, Heinrich I (eds.). TRACE - Tree Rings in Archaeology, Climatology and Ecology, Vol. 7. GFZ Potsdam. Scientific Technical Report STR 09/03. pp. 126-134.
• Close, D.C., N.J. Davidson, D.W. Johnson, M.D. Abrams, S.C. Hart, I.D. Lunt, R.D. Archibald, B. Horton, and M.A. Adams. 2009. Premature decline of Eucalyptus and altered ecosystem processes in the absence of fire in some Australian forests. Botanical Review 75:191-202. http://dx.doi.org/10.1007/s12229-009-9027-y.
• Jennings, M.D., D. Faber-Langendoen, R.K. Peet, O.L. Loucks, D.C. Glenn-Lewin, A. Damman, M.G. Barbour, R. Pfister, D.H. Grossman, D. Roberts, D. Tart, M. Walker, S.S. Talbot, J. Walker, G.S. Hartshorn, G. Waggoner, M.D. Abrams, A. Hill, M. Rejmank. 2009. Description, documentation, and evaluation of associations and alliances within the U.S. national vegetation classification. Special publication, Ecological Society of American. Washington, D.C. 79 pp.
• Johnson, S. and M. D. Abrams. 2009. Age class, longevity and growth rate relationships: protracted growth increases in old trees in the eastern United States. Tree Physiology. 12 pp. http://dx.doi.org/10.1093/treephys/tpp068.
• Sands, B. and M. D. Abrams. 2009. The effects of stump diameter on sprout number and size for three oak species in a Pennsylvania clearcut. Northern Journal of Applied Forestry 26(3):122-125.

Progress 10/01/07 to 09/30/08

Outputs
OUTPUTS: Physiological measurements were conducted during the 2008 growing season in understory plots receiving warming from heat lamps. Between five and seven study plants per species (red oak, chestnut oak, hickory (Carya), and red maple) per subplot were evaluated. Pre-dawn water potentials were estimated in one leaf per tree using a pressure chamber (Model 1000, PMS Instruments Co., Corvallis OR) at 0600 hours solar time. At mid-day (1100-1300 hours solar time) gas exchange measurements will be conducted on two fully expanded leaves. A portable photosynthesis unit (LCA-3, ADC Ltd, Herts, UK) was used to estimate net photosynthesis (A), leaf conductance to water vapor diffusion (gwv), leaf temperature (T leaf) and photosynthetic photon flux density (PPFD) for each leaf. Immediately following gas exchange measurements each leaf was harvested for water potential measurements, and processed for chemical and morphological analysis. Gravimetric soil moisture measurements were taken at 20 cm depth and soil nitrogen content measured at the Penn State Agricultural Analysis Center. Morphological measurements were made on leaves harvested for water potential measurements (two leaves per tree). Leaf area was measured using a leaf area meter (Li-Cor, Lincoln, NE) and the leaves were dried in a drying oven. Specific leaf mass will be calculated by dividing total leaf area (excluding petiole) by dry leaf weight. PARTICIPANTS: Marc Abrams TARGET AUDIENCES: Scientists, academics, State and Federal Agencies and land managers and private land owners involved with natural resource issues, including the PA DCNR and Federal DOD, DOE, NPS, Forest Service and BIA. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
When fire is suppressed in oak forests during the 20th century, they are rapidly invaded by later successional, fire sensitive species, such as maple (Acer), beech (Fagus), birch (Betula), and black gum (Nyssa). These species are now replacing oak and becoming dominant trees. I believe that the suppression of fire and the successional replacement of oak forests is a cause and effect relationship. Nonetheless, additional studies specifically addressing the fire and oak hypothesis, long-term burning studies in oak forests, and the direct dating of fire scars in old-growth oak forests are needed to resolve some of the remaining issues about the ecological role of fire in the development of oak forests. Moreover, fire is not the only factor that has influenced the ecology of oak forests during the 20th century. The impacts of acid rain, elevated CO2, potential global warming, herbivory, and gypsy moth outbreaks need to be studied in relation to the decline in oak recruitment and increase in later successional tree species in eastern oak forest. Throughout the eastern U.S., interactions and feedback among climate, vegetation, soils and topography, large- and small-scale disturbances, anthropogenic factors, and wildlife impacts created an ecological dynamic for oak forests that can only be understood from a long-term, multifactor perspective.

Publications

• Nowacki, G. J. and M. D. Abrams. 2008. Demise of fire and mesophication of eastern U.S. forests. BioScience. 58: 123-138.
• Abrams, M. D. and V. L. W. Hayes. 2008. Impacts of contrasting land-use history and soils on the composition and dynamics in mixed-oak, coastal plain forests on Shelter Island, New York, USA. Journal of the Torrey Botanical Club. 135: 37-52.