Abstract
Simulating long-term, landscape level changes in forest composition requires estimates of stand age to initialize succession models. Detailed stand ages are rarely available, and even general information on stand history often is lacking. We used data from USDA Forest Service Forest Inventory and Analysis (FIA) database to estimate broad age classes for a forested landscape to simulate changes in landscape composition and structure relative to climate change at Fort Drum, a 43,000 ha U.S. Army installation in northwestern New York. Using simple linear regression, we developed relationships between tree diameter and age for FIA site trees from the host and adjacent ecoregions and applied those relationships to forest stands at Fort Drum. We observed that approximately half of the variation in age was explained by diameter breast height (DBH) across all species studied (r2 = 0.42 for sugar maple Acer saccharum to 0.63 for white ash Fraxinus americana). We then used age-diameter relationships from published research on northern hardwood species to calibrate results from the FIA-based analysis. With predicted stand age, we used tree species life histories and environmental conditions represented by ecological site types to parameterize a stochastic forest landscape model (LANDIS-II) to spatially and temporally model successional changes in forest communities at Fort Drum. Forest stands modeled over 100 years without significant disturbance appeared to reflect expected patterns of increasing dominance by shade-tolerant mesophytic tree species such as sugar maple, red maple (Acer rubrum), and eastern hemlock (Tsuga canadensis) where soil moisture was sufficient. On drier sandy soils, eastern white pine (Pinus strobus), red pine (P. resinosa), northern red oak (Quercus rubra), and white oak (Q. alba) continued to be important components throughout the modeling period with no net loss at the landscape scale. Our results suggest that despite abundant precipitation and relatively low evapotranspiration rates for the region, low soil water holding capacity and fertility may be limiting factors for the spread of mesophytic species on excessively drained soils in the region. Increasing atmospheric temperatures projected for the region could alter moisture regimes for many coarse-textured soils providing a possible mechanism for expansion of xerophytic tree species.
Highlights
Over the past twenty years, a number of studies have documented the potential impacts of climate change on forest biomes, broad forest cover types, and the ranges of individual tree species in eastern North America [1,2,3,4]
Most of this research was based on correlations between current bioclimatic conditions and current distributions of forest types or tree species, which were extrapolated into the future using outputs from global or regional climate models to characterize future distributions. ese projections either implicitly or explicitly assumed that the current distributions of tree species approximate the range of environmental tolerances the species have adapted to over thousands of years and that absence of a species or community suggests the presence of bioclimatic conditions unsuitable for sustained regeneration and growth
Species composition and relative basal areas were similar for regional Forest Inventory and Analysis (FIA) site tree plots and Fort Drum forest inventory plots; the installation contained a significantly larger proportion of eastern white pine and oak species relative to FIA plots and lower relative basal area in species associated with poorly drained sites such as northern white cedar and black ash (Figure 2(a)). is may be an artifact of under sampling of forested wetlands in the Fort Drum inventory, a larger relative proportion of excessively drained, sandy soils on the installation that favor pine and oak species, or a combination of both
Summary
Over the past twenty years, a number of studies have documented the potential impacts of climate change on forest biomes, broad forest cover types, and the ranges of individual tree species in eastern North America [1,2,3,4]. A number of different approaches and tools are available to model changes in forest structure and function over time and space including tree and stand-level models (e.g., traditional growth and yield models [9], Climate-Forest Vegetation Simulator [10], species-specific niche models [11], process models [12], and dynamic global vegetation models (MC1) [13]. Species-age cohorts and site types that define limitations on establishment and growth are specified for each cell in a raster data structure, and life history attributes for each species of interest are used to model change in species composition and biomass over time. LANDIS-II has been shown to be a flexible and accurate tool for modeling changes in species composition and distribution over time as a function of climate change by accounting for a variety of natural and anthropogenic disturbances [19, 20]
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