Research at the Harvard Forest LTER covers a range of spatial scales from regional (~1000 km) to subregional (~100 km) to landscape (~10 km) to site (~1 km); (Figure 1). Many projects span more than one spatial scale (Table 1). Study areas are described in more detail below.

Figure 1.

Human land-use activities differ from natural disturbance processes and may elicit novel biotic responses and disrupt existing biotic:environmental relationships. The widespread prevalence of land-use requires that human activity be addressed as a fundamental ecological process and that lessons from investigations of land-use history be applied to the conservation and management of forested landscapes. Changes in the intensity of land-use and extent of forest cover in New England over the past 3 centuries provide the opportunity to evaluate the nature of forest response and reorganization to such broad-scale disturbance. Using a range of archival data and modern studies, we assessed historical changes in forest vegetation and land-use from the Colonial period (early 17th C) to the present across a 5000 km2 area in central Massachusetts (Figure 2) in order to evaluate the effects of this novel disturbance regime on the structure, composition and pattern of vegetation and its relationship to regional climatic gradients.

Figure 2.

Figure 3.
Cultural history in the region following European settlement in the 17th and 18th C has involved a gradual and continual increase in the human population with a pronounced change through time from a dispersed agrarian population to a progressively urbanized and suburbanized population as large-scale industry increased in the mid 19th C (Figure 3). Rapid deforestation for agriculture led to a landscape dominated by open fields and scattered woodlots in the mid 19th C when the land was very intensively used. Concomitant with the opening of agricultural lands in the mid-west and industrialization in the east, farmland was abandoned in New England and reverted naturally back to forest, a process that has continued to the present (Figure 4). The major objectives of this study and related paleoecological research across the same region (Fuller et al. 1997) are to determine the impact of this changing intensity of land-use on regional vegetation patterns and to compare the forest composition during the pre-settlement period and today.

Figure4.

Foster, D. Integration of long-term studies into the analysis and management of modern landscapes. Plenary Talk, International Association for Landscape Ecology, Duke University, March 16, 1997.

Foster, D. Ecosystem response to human disturbance - integrating approaches and results across scales. Synthesis in Ecology: Applications, Opportunities, and Challenges. National Center for Ecological Analysis and Synthesis. November 18-20, 1996.

Foster, D. 1995. Land-use history and four hundred years of vegetation change in New England. In B. L. Turner (ed.), Principles, Patterns and Processes of Land Use Change: Some Legacies of the Columbian Encounter. SCOPE Publication. John Wiley and Sons, New York. pp. 253-319.

Foster, D. 1993. Land-use history and transformations of the forest landscape of central New England. Pages 91-110 in S. T. A. Pickett and M. McDonnell (eds.), Humans as Components of Ecosystems: Subtle Human Effects and the Ecology of Populated Areas. Springer-Verlag, New York.

Foster, D., G. Motzkin, and B. Slater. 1998. Land-use history as long-term broad-scale disturbance: regional forest dynamics in Central New England. Ecosystems 1:96-119.

Fuller, J., D. Foster, J. McLachlan and N. Drake. 1998. Impact of human activity on regional forest composition and dynamics in Central New England. Ecosystems 1:76-95.

Motzkin, G., D. Foster, A. Allen, J. Harrod and R. Boone. 1996. Controlling site to evaluate history: vegetation patterns of a New England sand plain. Ecological Monographs 66:345-365.

Motzkin, G., W. Patterson and D. Foster. In review. A regional-historical perspective on uncommon plant communities: Pitch Pine-Scrub Oak in the Connecticut River Valley of Massachusetts. Journal of Ecology.

J. Aber, W. Currie, C. Driscoll, E. Farrell, C. Federer, C. Goodale, M. Goulden, J. Jenkins, D. Kicklighter, R. Lathrop, G. Lovett, M. Martin, S. McNulty, J. Melillo, S. Ollinger, K. Postek, P. Reich, R. Santore

We first discussed our approach for the Harvard Forest's contribution to regional studies at the LTER All-Scientists meeting in 1990. Working out from the heart of New England, and working with the Harvard Forest LTER theme of natural versus human disturbance, we chose the New York/New England region as the target area. This region encompasses a wide range of climatic zones and forest types, as well as significant gradients in pollutant deposition. We developed an approach (Aber et al. 1993) which combined a high resolution GIS with statistical models to summarize important climate drivers and a simple, lumped parameter model to predict water, carbon and nitrogen dynamics across the region. All of the components of this systems are now in place and have been used to derive site-level and region-wide estimates of forest NPP and water yield under current conditions and those predicted for the next century.

Figure 7.	Figure 8

Figure 9. Figure 10. Figure 11. Figure 12.

For the New England/New York regional GIS, a 30 arc-second (approximately 1 km.) digital elevation model (DEM, Figure 7) was obtained from the USGS, and a 1 km. land use/land cover (LULC) map (Figure 8) was derived from AVHRR satellite data that identifies current vegetation as hardwood, spruce-fir, pine and mixed forest types (Lathrop and Bognar, Rutgers University). In the absence of a successfully-validated soil WHC coverage (Lathrop et al. 1994), we have used a regional mean value of 12 cm. Mean monthly climate values are determined as functions of latitude, longitude and elevation, using a statistical climate model developed for the region in combination with the DEM (e.g. temperature Figure 9, precipitation Figure 10; Ollinger et al. 1995). Existing data on wet deposition and atmospheric concentrations of dry deposition components were used to derive regional patterns in deposition of all major ions (e.g. nitrogen Figure 11, sulfur Figure 12; Ollinger et al. 1993, 199 ). In concert with the development of the regional GIS we began to work on a new forest ecosystem model which would summarize accepted physiological controls on water, C and N dynamics in as simple a structure as possible, requiring only those inputs which could be defined within a regional GIS. The result of this effort to date is PnET, a nested series of lumped-parameter models of carbon, nitrogen and water fluxes in temperate and boreal forest ecosystems (Figure 13). The different versions of PnET are modular and build out from simplest to most complex. Algorithms such as photosynthesis which are common to all versions are identical between versions. Increasing complexity occurs by layering additional algorithms, representing additional processes, over the core processes in simpler or included versions.

Figure 13.

PnET-Day uses foliar mass, specific leaf weight, foliar N concentration, temperature and radiation flux to predict daily gross and net photosynthesis of whole forest canopies, and has been validated against daily summaries of eddy correlation carbon balance measurements from the Harvard Forest (Aber et al. 1996). PnET-II adds carbon allocation and respiration terms, as well as a full water balance to predict NPP, transpiration and runoff. An empirical soil respiration terms allows prediction of total ecosystem carbon balance under ambient conditions. This version has been validated against annual NPP and monthly water yield data from the Harvard Forest and Hubbard Brook ecosystems and is used to predict the combined effects of climate change and increased atmospheric CO2 on these processes (Aber et al. 1995). An earlier version (Aber and Federer 1992) was also validated against data from 10 additional forest types across North America, and a recent modification has extended the model to predict effects of tropospheric ozone concentrations (Ollinger et al. 1997).

PnET-CN adds compartments for woody biomass and soil organic matter, as well as algorithms for biomass turnover and litter and soil decomposition to allow calculation of complete carbon and nitrogen cycles. This version maintains the predictions for NPP and water balance used for validation in PnET-II, and also compares well with field data in predicting total annual, mean seasonal, and actual time series rates of nitrate loss in streams (Aber et al. 1997a, 1997b). An additional version of the model (PnET-BGC) is under development. This uses multiple element limitations on NPP and element concentrations in all pools to calculate cycling rates for all elements. This version has been combined with the soil chemistry model CHESS (Santore and Driscoll, Syracuse University) and used to predict stream and soil chemistry (Postek et al. 1995). Both the PnET-CN and PnET/CHESS versions represent significant collaborative efforts with Dr. Charles Driscoll and other cooperators from the Hubbard Brook LTER site.

Figure 14. Figure 15.

For regional productivity and water balances, PnET has been run for each pixel of the 1 km resolution GIS data base. Predicted outputs include annual net ecosystem production (Figure 14), net primary production, wood production and water yield (Figure 15). Regional validation of water yield predictions have been carried out using data summarized from gauged watersheds (Ollinger et al. 1997, Bishop et al. 1997). Initial assessments of climate change effects were made by Aber et al. (1995). Interactions with O3 have been addressed by Ollinger et al. (1996, 1997). Impacts of N deposition have been discussed relative to the ability of forest ecosystems to retain and cycle N under undisturbed (Aber et al. 1997a) and manipulated (Aber et al. 1997b) conditions. PnET has been used in other settings as well. A methodology similar to that described here has been used to develop soil and climate data planes, and to run PnET regionally to predict potential forest productivity under current and double CO2 conditions for Ireland, a country where afforestation is occurring rapidly (Goodale et al. 1997a,b). At the other extreme in spatial coverage, PnET has been used in conjunction with estimates of canopy chemistry obtained by high resolution remote sensing for the Prospect Hill tract at Harvard Forest (Martin and Aber 1996, 1997). Applications to sites in Japan, France and the Czech republic have been carried out and manuscripts are submitted or in preparation.

Aber, J.D. and C.A. Federer. 1992. A generalized, lumped-parameter model of photosynthesis, evapotranspiration and net primary production in temperate and boreal forest ecosystems. Oecologia 92:463-474.

Aber, J.D. and C.T. Driscoll. In review. Effects of land use, climate variation and N deposition on N cycling and C storage in northern hardwood forests. Global Biogeochemical Cycles.

Aber, J.D., C.T. 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 biogeochemical cycles in northeastern (U.S.) forests. Ecological Modeling 67:37-47.

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.D., S.V. Ollinger, C.A. Federer and C. Driscoll. In press. Modeling nitrogen saturation in forest ecosystems in response to land use and atmospheric deposition. Ecological Modelling.

Aber, J.D., 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.

Bishop, G.D., M.R. Church, J.D. Aber, R.P. Neilson, S.V. Ollinger and C. Daley. In review. A comparison of mapped estimates of long-term runoff in the northeastern United States. Journal of Hydrology.

Goodale, C.L., J.D. Aber and E.P. Farrell. In review. Applying an uncalibrated, physiologically based model of forest productivity to Ireland. Climate Research.

Goodale, C.L., J.D. Aber and S.V. Ollinger. Mapping monthly precipitation, temperature and solar radiation for Ireland with polynomial regression and a digitial elevation model. Climate Research.

Lathrop, R.G., J.D. Aber and J.A. Bognar. 1995. Spatial variability of digital soil maps and its impact on regional ecosystem modeling. Ecological Modeling 82:1-10.

Martin, M.E. and J.D. Aber. Estimating canopy characteristics as inputs for models of forest carbon exchange by high spectral resolution remote sensing. IN: Gholz, H.G., K. Nakane and H. Shimoda (eds.) The use of remote sensing in the modeling of forest productivity. Kluwer Academic, Dordrecht, The Netherlands, pp 61-72.

Martin, M.E. and J.D. Aber. 1997. Estimation of forest canopy lignin and nitrogen concentration and ecosystem processes by high spectral resolution remote sensing. Ecological Applications 7:431-443.

Ollinger, S.V., J.D. Aber and C.A Federer. In review. Estimating regional forest productivity and water yield using and ecosystem model linked to a GIS. Landscape Ecology.

Ollinger, S.V., J.D. Aber and P.B. Reich. Simulating ozone effects on forest productivity: interactions between leaf,- canopy- and stand-level processes. Ecological Applications.

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 Technical Report NE-191. 30p.

Ollinger, S.V., J.D. Aber, G.M. Lovett, S.E. Millham, R.G. Lathrop and J.M. Ellis. 1993. A spatial model of atmospheric deposition for the northeastern U.S. Ecological Applications 3:459-4.

Postek, K.M., C.T. Driscoll, J.D. Aber and R.C. Santore. 1995. Application of PnET-CN/CHESS to a spruce stand in Solling, Germany. Ecological Modeling 83:163-1.

E. Boose, K. Chamberlin, M. Serrano, D. Foster

This project is studying the long-term hurricane disturbance regimes of New England and Puerto Rico with a focus on the Harvard Forest (central Massachusetts) and the Luquillo Experimental Forest (LEF; northeastern Puerto Rico), two LTER sites with very different climate, topography, forest vegetation, and land-use history. Our approach combines historical research with computer modeling to reconstruct the impacts of past hurricanes at spatial scales ranging from site (~1 km) to landscape (~10 km) to regional (> 100 km).

Figure 16.
For each hurricane, reports of actual wind damage to trees, buildings, and other property are collected and indexed by town to create a database for each storm. Primary sources are newspapers for recent centuries and personal diaries and chronicles for earlier storms. Each report is assigned a Fujita scale (F-scale) value using the classification scheme proposed by T. Fujita for assessing wind damage in tornadoes and hurricanes. A map of actual wind damage for each hurricane is then created by using the maximum F-scale value for each town in the database (e.g. Hurricane Bob, Figure 16; Boose et al. 1997).

Regional wind conditions and wind damage are reconstructed for each storm using a simple meteorological model (HURRECON; Boose et al. 1997, Boose et al. 1994). The model utilizes data on the track, size, and intensity of a hurricane to reconstruct wind conditions at specific sites and regional gradients of wind speed and direction during a storm. The model can also predict damage on the Fujita scale using the correlations between peak wind speed and damage proposed by Fujita. In historical reconstructions the model provides informed estimates for sites lacking actual observations.

Figure 17.
The HURRECON model is parameterized for each region through detailed studies of recent hurricanes. All reconstructions are tested by comparing model results with available wind and damage data (e.g. Hurricane Bob, Figure 17). Input data for Atlantic hurricanes since 1886 are derived from the NOAA HURDAT database. For earlier hurricanes, storm tracks and maximum wind speeds are estimated from observed peak wind directions, observed storm surges, and the regional patterns of observed wind damage. Composite maps of long-term regional impacts are created by compiling the results of individual hurricane reconstructions.

At a landscape scale, local topography may create complex patterns of exposure to damaging winds. These topographic effects are estimated with a simple model of topographic exposure to wind (EXPOS; Boose et al. 1994). Wherever possible model results are compared with actual maps of landscape-level damage.

Figure 18.
Results to date for New England show strong gradients across the region from southeast (CT, RI, and southeastern MA coastlines) to northwest (northern VT, NH, and ME) both in maximum intensity and in frequency of hurricanes of a given intensity. These gradients resulted from the consistent direction of the storm tracks, the shape of the coastline, and the tendency for hurricanes to weaken rapidly over land or over cold ocean water. Twenty-six hurricanes were reconstructed for the period 1620-1885, and 36 hurricanes for the period 1886-1996. Average return intervals for F0 damage (defoliation, branch break, occasional blowdowns) ranged from 5 to 110 years; average return intervals for F1 damage (isolated blowdowns) ranged from 10 years to none in 110 years; and average return intervals for F2 damage (extensive blowdowns) ranged from 95 years to none in 375 years (Figure 18). Hurricane impacts at individual sites appeared to be clustered in time, with significant differences over relatively short distances (e.g. 100 km between Petersham, MA and Providence, RI, Figure 19). In Petersham (central Massachusetts) most of the landscape was apparently subject to F2 damage during the historical period, with small areas in protected valleys experiencing only F1 damage (Figure 20).

Figure 19.	Figure 20.
Figure 21.	Preliminary results for Puerto Rico also show gradients across the island from southeast to northwest in hurricane frequency and intensity, though all areas were subject to repeated damage from hurricane winds. Both frequency and intensity were significantly greater than in New England: preliminary estimates for 71 hurricanes during the period 1886-1996 showed average return intervals in the LEF of 11 years for F1 damage, 22 years for F2 damage (Figure 21), and 111 years for F3 damage. Hurricane impacts at individual sites appeared to be clustered in time, with significant differences over relatively short distances (e.g. 150 km between the LEF and Mayaguez, Figure 22). In the LEF, landscape-level damage during this 111 year period was dominated by F3 winds from the NE and E during the 1928 hurricane, with lesser damage (F2) on southwestern slopes and scattered pockets of minor damage (F1) or no damage in deep valleys or ravines (view toward south, Figure 23; view toward north, Figure 24. Future work will examine the major hurricanes of the earlier historical period, 1508-1885.
Figure 22.
Figure 23.	Figure 24.

The approach developed in this project can be used to study the impacts of past hurricanes in any part of the world where good historical records survive. Results can be combined with evidence of other past disturbances (e.g. fire, disease, human land-use) to build a more complete picture of long-term forest disturbance regimes for a particular region.

Boose, E. R., K. E. Chamberlin and D. R. Foster. 1997. Reconstructing historical hurricanes in New England. Pp. 388-389 in Preprints of 22nd Conference on Hurricanes and Tropical Meteorology, American Meteorological Society, Boston, MA.

Boose, E. R., D. R. Foster, and M. Fluet. 1994. Hurricanes impacts to tropical and temperate forest landscapes. Ecological Monographs 64: 369-400.

Foster, D. R., M. Fluet and E. R. Boose. In review. Human or natural disturbance: landscape-scale dynamics of the tropical forests of Puerto Rico. Ecological Applications.

Foster, D. R. and E. R. Boose. 1995. Hurricane disturbance regimes in temperate and tropical forest ecosystems. Pp. 305-339 in Wind and Trees. M. P. Coutts, ed. Cambridge University Press.

Foster, D. R. and E. R. Boose. 1992. Patterns of forest damage resulting from catastrophic wind in central New England, U.S.A. Journal of Ecology 80: 79-98.

Foster, D. R. 1988. Disturbance history, community organization and vegetation dynamics of the old-growth Pisgah Forest, south-western New Hampshire, U.S.A. Journal of Ecology 76: 105-134.

Foster, D. R. 1988. Species and stand response to catastrophic wind in central New England, U.S.A. Journal of Ecology 76: 135-151.

Regionalization studies at the Harvard Forest LTER have been supported by funds from the following sources: