Abstract
Land use and climate change have complex and interacting effects on naturally dynamic forest landscapes. To anticipate and adapt to these changes, it is necessary to understand their individual and aggregate impacts on forest growth and composition. We conducted a simulation experiment to evaluate regional forest change in Massachusetts, USA over the next 50 years (2010-2060). Our objective was to estimate, assuming a linear continuation of recent trends, the relative and interactive influence of continued growth and succession, climate change, forest conversion to developed uses, and timber harvest on live aboveground biomass (AGB) and tree species composition. We examined 20 years of land use records in relation to social and biophysical explanatory variables and used regression trees to create "probability-of-conversion" and "probability-of-harvest" zones. We incorporated this information into a spatially interactive forest landscape simulator to examine forest dynamics as they were affected by land use and climate change. We conducted simulations in a full-factorial design and found that continued forest growth and succession had the largest effect on AGB, increasing stores from 181.83 Tg to 309.56 Tg over 50 years. The increase varied from 49% to 112% depending on the ecoregion within the state. Compared to simulations with no climate or land use, forest conversion reduced gains in AGB by 23.18 Tg (or 18%) over 50 years. Timber harvests reduced gains in AGB by 5.23 Tg (4%). Climate change (temperature and precipitation) increased gains in AGB by 17.3 Tg (13.5%). Pinus strobus and Acer rubrum were ranked first and second, respectively, in terms of total AGB throughout all simulations. Climate change reinforced the dominance of those two species. Timber harvest reduced Quercus rubra from 10.8% to 9.4% of total AGB, but otherwise had little effect on composition. Forest conversion was generally indiscriminate in terms of species removal. Under the naive assumption that future land use patterns will resemble the recent past, we conclude that continued forest growth and recovery will be the dominant mechanism driving forest dynamics over the next 50 years, and that while climate change may enhance growth rates, this will be more than offset by land use, primarily forest conversion to developed uses.
Highlights
Climate and land use changes are two major global ecological concerns with the potential to transform forest landscapes
At the scale of the entire state, the LANDIS-II spinup of the initial forest condition resulted in an estimate of 181.83 total AGB (Tg) of aboveground biomass (AGB), which was within 15% of the total biomass estimated from the imputation of the Forest Inventory and Analysis (FIA) data conducted by B
The largest changes in AGB arose from continued stand growth and succession, irrespective of any climate or land use changes. This finding reflects the fact that the average forest carbon density present in the landscape is well below what is seen in old-growth forests. This process of continued AGB accrual is operationalized within the model vis-a -vis the initial forest biomass condition, which is based on forest inventory plots, and the maximum biomass parameters, which are based on empirical estimates taken from a sparse sample of oldgrowth forests, adjusted downward based on estimated productivity of the ecoregion
Summary
Climate and land use changes are two major global ecological concerns with the potential to transform forest landscapes. The combined influence of these largescale anthropogenic forces is being superimposed onto naturally (and culturally) dynamic systems. Too often the ecological consequences of these forces are considered independently (Dale 1997). Scientists and policy makers require integrated analyses of multiple interacting processes in order to anticipate and adapt to future global change. We have conducted a series of landscape simulations that incorporate and project forward the current trends in forest growth and succession, land use, Manuscript received 16 December 2010; revised 29 March 2011; accepted 11 April 2011.
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