| In western Great Smoky Mountains National Park (GSMNP), Tennessee, as in much of eastern North America, logging, agricultural clearing, and anthropogenic burning peaked in the mid 19th through early 20th centuries. I examined the effects of changes in disturbance regime on stand and landscape-level vegetation patterns using plot data from 1936--37, 1977--79, and 1995--96. Specifically, I asked: (1) have the site variables most strongly associated with landscape-level vegetation patterns remained constant through time, (2) what changes in vegetation composition and structure have occurred within groups of sites sharing similar environments and disturbance histories, and (3) have distributions of species along major environmental gradients changed through time?; Indirect gradient analyses using non-metric multidimensional scaling (NMDS) indicate that compositional variation during each time period was strongly correlated with elevation and topographic moisture. Comparisons of 1930s and 1970s plot data indicate that significant increases in canopy density, richness, basal area and biomass occurred on all site types. Castanea dentata disappeared from the forest canopy, and the relative abundance of shade-tolerant species increased. Several species largely restricted to mesic sites in the 1930s spread onto more xeric sites by the 1970s. Between the 1970s and 1990s, basal area, biomass, and density of canopy trees remained relatively constant. Relative abundance of shade-tolerant species continued to increase on all site types, and gradient distributions of several species contracted.; More detailed examination of xeric sites indicates that (1) age structure and radial growth patterns are highly consistent with conclusions based on historical plot data; (2) herbaceous richness and cover are higher during the first decade after fire than on environmentally similar sites that have not burned in >40 years; and (3) decreases in fire frequency have led to the decline of several species historically important on xeric sites.; Changes in vegetation composition and structure in western GSMNP appear to reflect forest development and recovery following disturbance in the late 19th and early 20th centuries and ongoing disturbance by introduced pathogens. Future disturbances and environmental changes will interact with legacies of past land-use to produce ongoing changes in stand and landscape-level vegetation patterns. |
