USING HISTORICAL CHANGE TO PREDICT FUTURE DISTRIBUTION OF HIGH ELEVATION FORESTS IN NORTHERN NEW ENGLAND

Funded by US DOE NICCR

Summary. We are investigating the effects of climate change on the dynamics and distribution of montane forest communities in northern New England. We are comparing the present and past species composition of vegetation plots that were established in the early 1960's in order to assess changes in forests associated with regional warming. We have documented a temperature increase of 0.9 to 1.7 degrees C over the last four decades accompanied by precipitation increases of 8 to 38 percent dependant on elevation. We have detected a significant change in forest composition and a rapid upslope shift of 70 to 120 m in the ecotone between low-elevation hardwood forests and high-elevation boreal forests over the last half-century. We are using future projections of regional climate to predict the distribution and composition of forests across New England, and are also investigating the potential for interactive effects of acid rain and climate change on regional forests.

Progress.  Our original project proposed to use study plots that span an elevational gradient from deciduous northern hardwood to high elevation conifer forests in conjunction with remote sensing data, dendrochronological techniques, and modeling to accomplish three objectives:

1. To quantify historical shifts of major forest types through resurveys of historic forest plots and comparison of historic and current aerial photographs and satellite images.
2. To attribute past shifts to proximate climatic and acid-deposition factors and their interactions using dendrochronological methods.
3. To forecast changes in forest distribution in response to projected climate change using a biogeographic model based on biophysical variables.

We have made significant progress over the first year of this grant on all three of these project objectives.  I describe below our progress with respect to each of these objectives.

Objective 1.  We are nearing the completion of a manuscript that describes the changes in composition of ecological communities and shifts in species distribution across an elevational gradient. These data include our most recent plot resurvey’s that are being compared to historic composition.  We are currently completing the analysis of our most recent plot resurveys using nonmetric, multidimensional scaling (NMDS) and Bayesian models. We use these data and analyses to address how species and ecological communities are likely to respond to climate change: Species may respond to this climate change in a largely similar manner with upslope range shifts that leaves ecological communities relatively intact.  Alternatively, species may respond individually to complex, multidimensional changes in climate, so that current species assemblages are disrupted.  In this case, current communities may not have analogs under future climates.  Our preliminary results indicate that communities are largely responding to documented increases in regional temperatures and precipitation as intact communities that respond synchronously to climate change.  We are completing an initial manuscript describing these results.  We will then examine the speed and magnitude of these changes along an acid deposition gradient in order to investigate the interaction between climate change and anthropogenic disturbance on vegetation responses.

Objective 2.  We have made progress on attributing both the rapidity of species shifts in response to regional change as well as variation in responses across the landscape to other interacting factors such acid rain impacts.  We have acquired a GIS database on spatial variation in acid deposition, bedrock resilience to acidification, and a combined index on resultant acid rain impacts.  We have concurrently identified available remote sensing imagery from across this region for use in estimating spatial and temporal rates of canopy mortality for comparison with a acid rain impacts, regional climate change, and rate of shift of vegetation.  Finally, we have begun to collect tree cores and online records of trees cores from across our study region in order to assess the impacts of climate change and acid rain on the growth of individual trees.  We expect that the comparison of ecological process on populations and communities across the landscape with growth patterns of individual trees will provide insight into the underlying mechanism driving the rate and variability of ecological change across the landscape.

Objective 3.  We have made substantial progress in forecasting the regional distribution of forests in response to projected regional climate change over this century, i.e., up to 2100.  We have retrieved archived climate data from three general circulation models (CGCM3.1, ECHAM5, and HadCM3) forced by three International Panel on Climate Change (IPCC) storylines (B1, A1B, and A2) that represent a broad range of potential greenhouse gas emission scenarios over this century.  We have downscaled these GCM data to our New England study region using observed climatic data from regional weather stations and have calculated changes for future climatic metrics such as temperature and precipitation on both annual and monthly bases for mid-century (2041-2070) and late century (2071-2100).  We are currently using these climatic data to drive two vegetation models, one equilibrial (i.e., Biome4) and one dynamic (i.e., LPJ), in order to project the regional distribution of forest or species types expected later this century in response to regional climate change.  We will continue this work with a first manuscript expected late this spring.