Harvard Forest Long Term Ecological Research Program
Background, Rationale and Design
Temperate forests are dynamic ecosystems that have been shaped through geologic and historical time by natural changes in the biotic and abiotic environment. Over millennial time scales climate variation has produced large shifts in the distribution and abundance of organisms, the intensity and return intervals of disturbance processes, and the productivity of ecosystems (Foster and Zebryk 1993). At century scales ecosystems have been impacted by broad-scale disturbance and long-term meteorological trends (Boose et al. 1994). On very short time scales interannual, seasonal, and diurnal variation has occured in both physical forcing factors and biotic response (Wofsy et al. 1993; Goulden et al. 1997). Retrospective research and long-term studies document that temperate forests have been remarkably resilient to this wide range of natural environmental change and physical disturbance (Foster et al. 1990).
Despite this apparent resiliency, novel human-imposed disturbances and stresses have impacted temperate regions with increasing frequency over past centuries and may surpass the ability of forests to recover and to control important ecosystem processes (Aber et al. 1989). Massive land-use change has altered the extent and structure of forests as well as hydrological, meteorological and pedological processes. Changes in the global earth-atmosphere system have resulted in significant increases in the deposition of air pollution and may rapidly alter energy budgets in north temperate regions (Bazzaz 1996, Melillo et al. 1995). Introduced pathogens and exotic organisms continue to produce selective changes in the abundance of major forest species (Foster 1993). An important question facing ecologists, natural resource managers, and policy makers is: are temperate forests as resilient (and/or resistant) to these novel physical, chemical and climatic stresses as they are to natural disturbance and environmental change?
In 1988 the Harvard Forest Long Term Ecological Research program was initiated to address this and related questions through an analysis and comparison of important natural disturbances, environmental change and historical and projected human impacts in terms of their effect on ecosystem structure, composition and function. Among the suite of disturbance and stress processes investigated emphasis has been placed on (1)hurricane and other wind impacts, (2) climate change, (3) changing land-use and land cover, (4) altered atmospheric chemistry and increased nitrogen deposition, and (5) projected increases in global temperature.
Our research design has involved assembling an interdisciplinary group of scientists that uses three complementary approaches to long-term study: (1) retrospective research that employs paleoecological, archaeological, dendrochronological and other historical techniques to interpret past conditions and the development of modern ecosystem structure and function, (2) ongoing measurements that assess current structure and function and allow the detection of variation and future change, and (3) experimental manipulations that enable the integrated study of ecosystem response to specific disturbances and stresses under relatively controlled conditions (Table 1). Through studies across a broad range of spatial and temporal scales we seek to understand the modern forest landscape of central New England, to develop information and approaches with broad relevance to fundamental ecological issues, and to train researchers and develop databases that have strong application to societally-relevant environmental concerns (Table 2, Fig. 1).
Forest Dynamics in Central New England
The landscape of central New England has been highly dynamic over the past few thousand years as environmental factors that control forest structure, composition and ecosystem processes have changed continuously, though at variable rates (Foster and Zebryk 1993, Fuller et al. 1997). The broad-scale physiographic template has been relatively unaltered since the last glaciation shaped the gentle hill and valley topography and left a variable thickness of till and stratified deposits some 13,000 years ago. However, climate, on a century to millennial time-frame, has undergone continual change in temperature, precipitation and their seasonal distribution (Fig. 2). Even over the last century there exist annual variation, short-lived changes, and lengthy trends that are relevant to forested ecosystems, and the physical processes and biotic constituents that shape them (Aber et al. 1995).
Reconstructions of forest dynamics suggest that natural disturbance processes, ranging from frequent small events to infrequent large and catastrophic impacts have played an important role in structuring the pattern and processes of natural ecosystems across New England (Foster 1988). Nearly 5000 years ago a remarkably abrupt and major decline in hemlock occurred throughout its range in New England and across the Northeast, presumably as a consequence of infestation from a novel pathogen. Over the subsequent 1000-year period forest ecosystems underwent pronounced changes as hemlock gradually recovered, although with considerable regional to local variation in the response and recovery patterns (Fuller et al. 1997). The historical record of major hurricane impacts every 75-100 years leads to speculation that infrequent catastrophic disruption by tropical storms may play an important role in structuring the forest vegetation of New England over long time periods (Fig. 3 and Fig. 4; Boose et al. 1994). Given the propensity for such storms to weaken over land and to exhibit relatively constrained patterns of movement across New England, it is quite possible that pronounced regional gradients and specific landscape-scale patterns of historical impact may interact with broad-scale environmental and physiographic patterns in controlling vegetation structure and composition (Foster and Boose 1995). Long-term records and the ubiquitous presence of mound and pit topography in old forest stands suggest that finer-scale disturbances such as gap dynamics, downbursts and tornadoes have contributed more local patterning to forests over the ages. The relative role of these different types and scales of physical disturbance and their spatial distribution across the landscape and region are largely unknown.
Although infrequent, perhaps occurring as rarely as once every thousand years in some regions and forest types, or ten times as frequently in others, fire has played an uncertain and variable role in New England forests (Fuller et al. 1997). The topic of fire invariably introduces the role of humans, for it is in the purposeful use of fire that aboriginal people may have exerted a widespread, though subtle impact on natural vegetation. For the New England region the general patterns of aboriginal activity are well known: A highly variable geographic pattern with dense settlements on the coast, coastal islands, and along major river valleys and sharply lower population in upland areas; a dynamic history of changing cultural patterns, seasonal activities and density that varied with climate and major changes in forest composition that altered the availability of important food sources such as nut-bearing trees and wildlife; and the late introduction of maize agriculture within the past 1000 years (Mulholland 1984, 1988). Much speculation exists on how these geographic and temporal patterns of activity interacted with and altered the natural ecosystem patterns. In particular, the extent of forest clearance for agriculture and the role of fire in pre-European times remain a major issue.
Over the past 350 years since European settlement the rate of ecosystem change has accelerated and the landscape of New England has been transformed (Foster et al. 1997b). Despite a steadily increasing human population, major cultural and technological shifts have led to a region-wide historical pattern of extensive deforestation through the mid to late 19th C followed by broad-scale abandonment of agriculture and massive natural reforestation (Fig. 5 and Fig. 6). Vast areas of New England that once supported scattered, cut-over woodlots in a matrix of fields and pastures are now covered with aggrading second-growth forest that ranges across 65-85% of the uplands. Excluding northern Maine, the new forests of the New England states bear much evidence of the agricultural past of pasture, cropland, and woodlot: stonewalls separating contrasting forest stands, old cellar holes and collapsed dams, and wood trails and dirt road remnants of colonial transportation networks. As the forest area and size have recovered regionally so have the native fauna and regional ecosystem processes (Motzkin et al. 1996). In many ways the landscape of rural New England appears more natural than at any time since the 1700s. The major question that looms is: how has this massive land-use disturbance altered the natural forest pattern and process and what legacies has it left in the new forest landscape?
In recent decades the forests and environment of New England have been exposed to more novel types of anthropogenic stress. A series of introduced pathogens - chestnut blight, Dutch elm disease, gypsy moth, beech bark disease, and hemlock woolly adelgid - has selectively weakened, defoliated or decimated major tree species across the region (Fig. 7; Orwig and Foster 1997). Industrialization has led to pronounced changes in the earth's atmosphere that are leading to increased, though geographically variable, increases in the deposition of nitrogen (a major limiting nutrient in most terrestrial ecosystems) and sulphur in forms that acidify precipitation as well as the ecosystems that they impact (Fig. 8; Aber et al. 1993, 1997). While photochemcial reactions in the upper atmosphere deplete the tropospheric ozone layer that shields the earth from ultraviolet radiation, stagnant circulation patterns during the summer growing season bring damaging ozone episodes up the east coast to interior New England forests (Goulden et al. 1997; Munger et al. 1996). Increases in major greenhouse trace gases - CO2, CH4, and N2O may be leading to a regional annual increase of temperature of 3-4oC within the next century. Meanwhile, the increase in CO2 (as well as N and O3) may be having subtle, though important, consequences on plant performance and ecosystem processes (Bazzaz and Miao 1993; Bazzaz et al. 1996) . The interaction and comparative impact of these novel stresses with historically important disturbance processes is a major issue for ecologists and concern for natural resource managers.
As we seek to understand the current structure, composition, and process of forest ecosystems in central New England it is essential that we develop a perspective that incorporates the historically important as well as currently operative environmental factors that control these ecosystems (Foster et al. 1992, 1996). It is also important to frame questions and approaches that are regionally and societally relevant and that have general applicability to the understanding of terrestrial forest ecosystems.
Ecological Questions Concerning New England Forests
This brief overview of New England history highlights many changes in the physical, biotic and human environment that have led to a range of dynamics in terrestrial and aquatic ecosystems. Although the specific details may vary, the questions that are central to understanding current conditions and processes in this landscape and the application of that information in the anticipation and management of future change, are broadly relevant to all natural ecosystems.
What are the historically important environmental factors and disturbance processes that have shaped forest ecosystems and landscapes in the region? The preceding has raised many questions concerning the way in which environmental change, natural disturbance, and human activities have operated at a stand to regional scale and through time. Of specific interest are the details of the natural disturbance regimes, the intensity, frequency, impact and geographic variation in wind, pathogens and fire, and the way in which these have interacted with pre-historic and historical human activity.
What is the contrasting effect of natural, physical disturbance versus novel anthropogenic stress on forest ecosystem function? Increasingly, forest ecosystems are being subjected to chemical and climatic stresses that are qualitatively novel or exceed the previous range in dose or rate of natural change. Recognizing that forest species evolved within a context of natural disturbance, it is important to assess whether forest ecosystems retain the same degree of control over ecosystem processes (e.g., nutrient cycling, hydrology) under novel conditions as they do under historically-important disturbances.
What is the magnitude of forest ecosystem response to intensive, regional land-use activity and how persistent are the physical and biological legacies of this historical disturbance? Large areas of northwestern Europe, Latin America, and eastern North America have or are undergoing a landscape transformation analogous to the forest - deforestation - reforestation history of New England. Major issues emerge at a regional to site scale concerning the process of forest recovery from such intensive disturbance, the ability of forest structure, composition and process to return to pre-disturbance conditions, and the duration of the impacts of historical land-use on community and ecosystem characteristics.
What application do answers to these questions have for ecological theory and policy-relevant issues such as understanding (a) global earth systems (e.g., CO2 exchange, response to global change); (b) forest ecosystem response to multiple stresses and disturbances; (c) the ability of natural ecosystems to be resistant or resilient to natural versus human disturbance; and (d) the contribution of long-term and retrospective approaches of ecological research to the interpretation and management of natural ecosystems? As we develop an improved understanding of modern forest ecosystems, their history of change and the anticipated magnitude of future change we can bring this information to bear on fundamental ecological questions concerning the patterns and process of natural ecosystem organization and dynamics. We can also assist in the application of this information to education and the management of our natural environment and resources.
Design and Structure of the Harvard Forest LTER Program
In order to address the ecological questions raised above, the research effort at the Harvard Forest has been organized to integrate studies across disciplines, scientific approaches and a wide range of spatial scales (Foster et al. 1997a). By seeking to augment the existing long-term record of ecosystem change at the Harvard Forest we have selected historically-important and currently relevant processes for extended investigation. Finally, we have expanded existing programs at the Harvard Forest in order to make public outreach and the education of a broad range of students a major product of these investigations (Table 1).
We use a complementary suite of scientific approaches in order to identify important ecological processes, create a very long-term series of measurements, and assess ecosystem response and dynamics. Retrospective studies utilize a range of paleoecological, dendroecological, historical, and modeling approaches to assess environmental, human and biological dynamics over scales of decades to millennia. These studies provide key insights into ecological processes as well as assist in the establishment of baseline conditions and the selection of important phenomena for studies or experimental manipulations (Foster et al. 1992). Ecological history revealed through retrospective studies provides insights into the range of environmental conditions and natural and human disturbance processes that have been historically operative in a landscape. This information enables us to identify processes and ranges of responses that are critical to study in order to understand ecosystem structure and process. It also contributes to an understanding of the relative role of historical factors versus environmental factors in controlling modern conditions. Many critical ecological processes, such as broad-scale disturbance, succession, ecosystem development, and migration operate on decadal to millennia time-scales that are difficult or impossible to measure through conventional studies. Reconstructive techniques enable the evaluation of such processes, frequently providing multiple examples to contrast and compare and may allow these observations to be placed within the context of post-glacial and geological environmental change (Foster and Zebryk 1993).
Long-term measurements of ecosystem structure, composition, process and dynamics are a central part of HF LTER that are conducted in diverse ways. Permanent plots and repeat sampling enables us to continue long-term observations that were initiated in the early 20th C at the Harvard Forest. Remote sensing provides a means of scaling some measurements across two or more of our spatial scales of observation (e.g., plot to landscape to region) at intervals of a decade or more (Martin and Aber 1997a, b). Control areas, coupled with experimental studies, provide baseline measurements and may be linked with flux studies of atmosphere-biosphere exchange at the environmental measurement station, which provides integrated ecosystem measurement of physical and biological processes (Aber et al. 1996. Wofsy et al. 1993).
In order to evaluate infrequent though historically important processes, and to anticipate ecosystem response to predicted ranges of climatic and chemical stresses, we have undertaken a series of long-term measurements on experimental field manipulations and under controlled environmental conditions in growth chambers and glasshouses (Bazzaz 1997). These studies have focussed on a subset of extremely important, though contrasting disturbances and stresses. Field manipulations ( Fig. 9) have included simulation of windthrow from a major hurricane (Cooper-Ellis and Foster 1997, Bowden et al. 1993a), clearcutting, enhanced deposition of N (Magill et al. 1997), soil warming as a component of climate change (Peterjohn et al. 1993, 1995), and alteration of above-and below-ground inputs of organic matter to soils (Bowden et al. 1993b). In the case of historically important processes such as hurricanes and forest harvesting, results of these studies can be compared directly to long-term measurements on "natural experiments," such as the 1938 hurricane or land-use history, that have occurred through time in the Harvard Forest. Other manipulations can be compared to parallel studies in other ecosystems (e.g., N saturation at Bear Brook; soil warming at Abisko, Sweden; organic matter manipulation at University of Wisconsin). In all cases, the integrated measurements of ecosystem structure and pattern enable comparison among these important manipulations.
Controlled environment studies have taken advantage of an unusually complete experimental facility at Harvard University in order to evaluate plant response to particular changes in key environmental resources, including moisture, light, nutrients and CO2 (Bernston and Bazzaz 1997a, b). The coupling of response measurements under laboratory control with those obtained from field experiments and under natural conditions make it possible to understand the separate and interactive effects of specific resources on plant and ecosystem function (Crabtree and Bazzaz 1993a, b).
Long-term studies that include the development of suites of measurements of ecosystem pattern and process can link with and carry forward observations of current condition and results from reconstructive studies. In particular, extended ecosystem measurements provide assessments of seasonal and interannual variation, long-term trends and trajectories, and ecosystem function under varied and contrasting conditions. The baseline assessments of ecosystem pattern and process represent a framework for long-term experimental manipulations that seek to provide integrated measurement of ecosystem response to infrequent disturbances (e.g., windstorm or fire), to historically important events (e.g., gypsy moth defoliation), to anticipated stresses within the range of expected conditions (e.g., enhanced atmospheric deposition of nitrogen), or to novel stresses resulting from human activity (e.g., global change). The coupling of retrospective studies and long-term measurement of intact and experimentally manipulated ecosystems consequently enables an integrated assessment of ecosystem dynamics and function under a range of historical, modern and simulated conditions (Foster et al. 1997b).
Spatial Scales of Investigation
Research in the Harvard Forest LTER operates at four primary scales: site, landscape, sub-region and region (Fig. 1). Intensive, individual-investigator studies at the scale of individual organisms, a sample plot, and study site represent the heart of our long-term research. Most of these studies occur on the three main tracts of the Harvard Forest (approximately 1200 ha) where great diversity of vegetation, site conditions, and history, ninety-years of continuous long-term studies, and ease of access to sites and laboratories provide ideal conditions for long-term measurements and experimental manipulations (Fig. 9). Infrastructural improvements such as access to below-ground electrical and communications service into the center of one tract, development of canopy access and environmental measurement towers, extensive deer exclosures, and control of vehicular access enable a wide array of experiments to be conducted under secure conditions. GIS-based data management systems enable current field sampling to be integrated with such diverse sources of information as low elevation airborne sensing, satellite imagery, radiotelemetry traces, and historical surveys and vegetation maps.
Many important processes, including natural and human disturbance and hydrology occur at a landscape scale where physiography, slope position, or vegetation pattern may determine environmental conditions (Foster and Boose 1992). In central New England, the area of an individual township (approximately 10 x 10 km) captures substantial landscape variation within the general physiographic setting of small-scale relief and gentle hill and valley topography that has a general south to north orientation. The town of Petersham, Massachusetts serves as one of our central areas for landscape studies as it includes the major tracts of the Harvard Forest and represents a typical upland rural village in New England. Given the politically independent structure of New England government, much of the geographical, social and environmental data relevant to ecological studies is collected or aggregated by public agencies at a township level making this a particularly convenient scale of study (Foster 1992). LTER studies on the Petersham landscape have the added advantage of access to a unqiue historical data base that has developed through 90 years of study of the town by Harvard Forest scientists.
In order to place site and landscape-level studies in a broader context and to examine variation in environmental, social and biotic processes, considerable research is conducted on the sub-region of central Massachusetts (Foster et al. 1997b; Golodetz and Foster 1997) and the regional-scale of New England and adjacent New York (Ollinger et al. 1995). Selection of these study areas was based both on ecological and pragmatic motivations. The central Massachusetts region (approximately 3560 km2) extends 100 km east of the Connecticut River Valley through the central upland region into the eastern lowlands west of Boston, and south from the New Hampshire border approximately half-way (50 km) to the Connecticut border (Fig. 1). Petersham and the Harvard Forest lie approximately in the center of the area. The region encompasses a wide range of the physical and biological variation of inland Massachusetts as well as substantial variation in social history through aboriginal and European times (Fuller et al. 1997). The ability to place intensive studies within the context of major cultural and environmental gradients is extremely useful for interpreting results from the Harvard Forest and for understanding the broad-scale controls over major ecological processes. On the practical side, the study area comprises 50 townships in four counties, which present a major though manageable challenge for the collection and management of archaeological, historical and modern data. Data for this region are primarily of three kinds - continuous spatial coverage (e.g., elevation, cover maps), township level (e.g., population, agricultural and forestry statistics), or site-specific (e.g., sample plots, pollen sites).
Considerably greater variation in environmental conditions occurs across the New England region and the dynamics and impacts of many of the important disturbance processes and modern anthropogenic stresses such as air pollution deposition can only be understood at this scale. In order to evaluate processes that are relevant at the regional scale we are conducting a select number of studies utilizing diverse historical, modern and modeling approaches. These studies yield data that may be continuous, aggregated at the county scale, or site specific. At the heart of these efforts are questions relating regionalization or extrapolation of point data to larger spatial scales and the use of models to project current results into a changing future.
Education Integrated with Research
Interdisciplinary ecological research programs based at established field institutions provide much more than insights into important scientific questions; they also afford the opportunity to train the next generation of scientists and to convey information to an interested public audience. Education thus forms an essential part of the HF LTER program, providing both a means for developing science and an outlet for disseminating it. Students are directly integrated into our ecological studies. A summer research program brings 20-25 undergraduates and recent graduates to the Forest to work on all projects, to undertake independent studies, and to learn how science is conducted by large research groups representing diverse institutions and comprised of faculty, staff and technical scientists, post-doctoral associates, graduate students, and administrators (Fig. 10). Graduate students from the MS and PhD programs of many northeastern universities pursue thesis studies as part of this effort and the Bullard Fellowship Program for Forest Research at Harvard Forest annually enables 4-8 mid-career faculty and professionals from around the world to interact with LTER researchers. Finally, permanent exhibits, scientific poster displays, and audio-visual programs at the Fisher Museum expand on research results and inform more than 5000 visitors annually about the natural history and management of New England forests.
Thus, the Harvard Forest has a major commitment to long-term research on important ecological issues in the temperate forests of eastern North America and the application of these results of fundamental ecological questions and management concerns on a local to global scale. In approaching this research we take a very strong historical perspective and attempt to place site-specific studies within a broad regional context. As these studies unfold we seek to involve researchers from diverse fields and perspectives and students of all kinds in our activities.
Aber, J. D., S. V. Ollinger, C. A. Federer and C. Driscoll. 1997. Modeling nitrogen saturation in forest ecosystems in response to land use and atmospheric deposition. Ecological Modelling (In press).
Aber, J. D., P. B. Reich and M. L. Goulden. 1996. Extrapolating leaf CO2 exchange to the canopy: a generalized model of forest photosynthesis validated by eddy correlation. Oecologia 106: 257-265.
Aber, J. S., S. V. Ollinger, C. A. Federer, P. B. Reich, M. L. Goulden, D. W. Kicklighter, J. M. Melillo and R. G. Lathrop, Jr. 1995. Predicting the effects of climate change on water yield and forest production in the northeastern U.S. Climate Research 5: 207-222.
Aber, J. D., C. Driscoll, C. A. Federer, R. Lathrop, G. Lovett, J. M. Melillo, P. Steudler and J. Vogelmann. 1993. A strategy for the regional analysis of the effects of physical and chemical climate change on biogeographical cycles in northeastern (U.S.) forests. Ecological Modelling 67: 37-47.
Aber, J. D., K. J. Nadelhoffer, P. Steudler and J. M. Melillo. 1989. Nitrogen saturation in northern forest ecosystems - hypotheses and implications. BioScience 39: 378-386.
Bazzaz, F. A. 1997. Allocation of resources in plants: state-of-the-science and critical questions. In: F. A. Bazzaz and J. Grace (eds.), Resource Allocation in Plants and Animals. Physiological Ecology Series of Academic Press, San Diego (In Press).
Bazzaz. F.A. 1996. Plants in Changing Environments: Linking Physiological, Population, and Community Ecology. Cambridge University Press, Cambridge, England.
Bazzaz, F. A. and S. L. Miao. 1993. Successional status, seed size and responses of tree seedlings to CO2, light, and nutrients. Ecology 74: 104-112.
Bazzaz, F. A. S. L. Bassow, G. M. Berntson and S. C. Thomas. 1996. Elevated CO2 and terrestrial vegetation: implications for and beyond the global carbon budget. Pp. 43-76 In: B. Walker and W. Steffen (eds.), Global Change and Terrestrial Ecosystems. Cambridge University Press.
Berntson, G. M. and F. A. Bazzaz. 1997a. Nitrogen cycling in microcosms of yellow birch exposed to elevated CO2: simultaneous positive and negative feedbacks. Global Change Biology (In press).
Berntson, G. M. and F. A. Bazzaz. 1997b. Belowground positive and negative feedbacks on CO2 growth enhancement. Plant and Soil (In press).
Boose, E. R., D. R. Foster and M. Fluet. 1994. Hurricane impacts to tropical and temperate forest landscapes. Ecological Monographs 64: 369-400.
Bowden, R., M. C. Castro, J. M. Melillo, P. A. Steudler and J. D. Aber. 1993a. Fluxes of greenhouse gases between soils and the atmosphere in a temperate forest following a simulated hurricane blowdown. Biogeochemistry 21: 61-71.
Bowden, R. D., K. J. Nadelhoffer, R. D. Boone, J. M. Melillo and J. B. Garrison. 1993b. Contributions of aboveground litter, belowground litter, and root respiration to total soil respiration in a temperate mixed hardwood forest. Canadian Journal of Forest Research 123: 1402-1407.
Cooper-Ellis, S. and D. R. Foster. 1997. Response of forest ecosystems to catastrophic wind: evaluating vegetation recovery on an experimental hurricane. Ecology (In Review).
Crabtree, R. C. and F. A. Bazzaz. 1993a. Seedling response of four birch species to simulated nitrogen deposition: ammonium versus nitrate. Ecological Applications 3: 315-321.
Crabtree, R. C. and F. A. Bazzaz. 1993b. Black birch (Betula lenta L.) seedlings as foragers for nitrogen. New Phytologist 122: 617-625.
Foster, D. R. 1993. Land-use history and forest transformations in central New England. Pp. 91-110 In: S. Pickett and M. McDonald (eds.), Humans as Components of Ecosystems. Springer-Verlag, NY.
Foster, D. R. 1992. Land-use history (1730-1990) and vegetation dynamics in central New England, USA. Journal of Ecology 80: 753-772.
Foster, D. R. 1988. Disturbance history, community organization and vegetation dynamics of the old-growth Pisgah Forest, southwestern New Hampshire, U.S.A. Journal of Ecology 76: 105-134.
Foster, D. R. and E. R. Boose. 1995. Hurricane disturbance regimes in temperate and tropical forest ecosystems. Pp. 305-339 In: M. Coutts and J. Grace (eds.), Wind and Trees. Cambridge University Press, Cambridge.
Foster, D. R. and E. R. Boose 1992. Patterns of forest damage resulting from catastrophic wind in central New England, USA. Journal of Ecology 80: 79-99.
Foster, D. R. and T. M. Zebryk. 1993. Long-term vegetation dynamics and disturbance history of a Tsuga-dominated forest in New England. Ecology 74: 982-998.
Foster, D. R., D. A. Orwig and J. S. McLachlan. 1996. Ecological and conservation insights from reconstructive studies of temperate old-growth forests. Trends in Ecology and Evolution 11: 419-424.
Foster, D. R., J. D. Aber, J. M. Melillo, R. Bowden and F. Bazzaz. 1997a. Temperate forest responses to natural catastrophic disturbance and chronic anthropogenic stress. BioScience (In Press).
Foster, D. R., G. Motzkin, B. Slater. 1997b. Land-use history as long-term broad-scale disturbance: regional forest dynamics in central New England. Ecosystems (In review).
Foster, D. R. , T. Zebryk, P. Schoonmaker and A. Lezberg. 1992. Post-settlement history of human land-use and vegetation dynamics of a hemlock woodlot in central New England. Journal of Ecology 80: 773-786.
Foster, D. R., P. K. Schoonmaker and S. T. A. Pickett. 1990. Insights from paleoecology to community ecology. Trends in Ecology and Evolution 5: 119-122.
Fuller, J., D. R. Foster, J. McLachlana nd N. Drake. 1997. Impact of human activity and environmental change on regional forest composition and dynamics in central New England. Ecosystems (In review).
Golodetz, A. D. and D. R. Foster. 1997. History and importance of land use and protection in the North Quabbin region of Massachusetts (USA). Conservation Biology 11: 227-235.
Goulden, M. L., J. W. Munger, S.-M. Fan, B. C. Daube and S. C. Wofsy. 1997. Effects of interannual climate variability on the carbon dioxide exchange of a temperate deciduous forest. Science (submitted).
Magill, A. H., J. D. Aber, J. J. Hendricks, R. D. Bowden, J. M. Melillo and P. A. Steudler. 1997. Biogeochemical response of forest ecosystems to simulated chronic nitrogen deposition. Ecological Applications 7: 402-415.
Martin, M. E. and J. D. Aber. 1997a. Estimation of forest canopy lignin and nitrogen concentration and ecosystem processes by high spectral resolution remote sensing. Ecological Applications (In press).
Martin, M. E. and J. D. Aber. 1997b. Estimating forest canopy characteristics as inputs for models of forest carbon exchange by high spectral resolution remote sensing. In: H. Gholz (ed.), The Use of Remote Sensing in the Modeling of Forest Productivity at Scales from the Stand to the Globe. Kluwer Academic Publishers, The Netherlands (In press).
Melillo, J. M., D. W. Kicklighter, A. D. McGuire, W. T. Peterjohn and K. Newkirk. 1995. Global change and its effects on soil organic carbon stocks. Pp. 175-189 In: R. Zepp et al. (eds.), Report of the Dahlem Workshop on the Role of Nonliving Organic Matter in the Earth's Carbon Cycle. John Wiley and Sons.
Motzkin, G., D. R. Foster, A. Allen, J. Harrod and R. D,. Boone. 1996. Controlling site to evaluate history: vegetation patterns of a New England sand plain. Ecological Mongraphs 66: 345-365.
Mulholland, M. 1984. Patterns of change in prehistoric southern New England, a regional approach. PhD Thesis, University of Massachusetts, Amherst.
Mulholland, M. 1988. Territoriality and horticulture, a perspective for prehistoric southern New England. Pp. 137-166 In: G. P. Nichols (ed.), Holocene Human Ecology in Northeastern North America. Academic Press, NY.
Munger, J. W., S. C. Wofsy, P. S. Bakwin, S.-M. Fan, M. L. Goulden, B. C. Daube and A. H. Goldstein. 1996. Atmospheric deposition of reactive nitrogen oxides and ozone in a temperate deciduous forest and a sub-arctic woodland. I. Measurements and mechanisms. Journal of Geophysical Research 101: 12639-12657.
Ollinger, S. V., J. D. Aber, C. A. Federer, G. M. Lovett and J. M. Ellis. 1995. Modeling physical and chemical climatic variables across the northeastern U.S. for a geographic information system. U.S.D.A. U.S. Forest Service General Tech. Report NE-191. 30 pp.
Orwig, D. and D. R. Foster. 1997. Forest response to the introduced hemlock woolly adelgid in southern New England. Bulletin of the Torrey Botanical Club (In review).
Peterjohn, W. T., J. M. Melillo, P. A. Steudler, K. M. Newkirk, F. P. Bowles and J. D. Aber. 1995. Responses of trace gas fluxes and N availability to experimentally elevated soil temperatures. Ecological Applications 4: 617-625.
Peterjohn, W. T., J. M. Melillo, F. P. Bowles and P. A. Steudler. 1993. Soil warming and trace gas fluxes: experimental design and preliminary flux results. Oecologia 93: 18-24.
Wofsy, S. C., M. L. Goulden, J. W. Munger, S.-M. Fan, P.S. Bakwin, B. C. Daube, S. L. Bassow and F. A. Bazzaz. 1993. Net exchange of CO2 in a mid-latitude forest. Science 260: 1314-1317.