چکیده (انگلیسی):

Multifactor ecosystem classification systems are designed to identify similar site units across the landscape based on repeating patterns of geomorphology, soil, and vegetation. Ecosystem classification models have been developed for numerous forest landscapes in North America and elsewhere, but few studies have employed multifactor classification techniques across forest disturbance and age gradients. With its myriad of landforms and history of logging, the 17,604-ha Jocassee Gorges tract in upstate South
Carolina of the southern Appalachian Mountains, USA, represents an ideal landscape to examine both spatial and temporal variability in vegetation–environment relationships. We examined a dual ecosystem and forest-age gradient, including five ecosystem types (ranging from xeric, upland Quercus ecosystems to moist, Tsuga canadensis ecosystems) and four forest-age classes (5–25, 26–50, 51–70, and >70 years old) within ecosystems. On 111 replicate 0.1-ha plots across the gradient, we sampled species composition of tree and ground-flora stratum, which we analyzed using permutation and ordination multivariate techniques. Overall differences in species composition for both strata occurred among ecosystems within all forest ages, and differentiation among ecosystems strengthened as forests aged. Age-related variation was evident within an ecosystem type for several ecosystems, but was generally weaker than variation among ecosystems. Ground flora was generally most sensitive to the age and ecosystem gradient, but the tree stratum also differed among age classes and several ecosystems. Forest composition across this landscape was filtered primarily by distribution of ecosystems serving as the physical template and secondarily by forest ages within ecosystems. Application of ecosystem classification to the full range of forest ages on the landscape also illuminated numerous considerations for forest management, such as a finding that of the three Quercus ecosystems on the landscape, a submesic ecosystem may be least resistant and resilient for maintaining Quercus dominance following logging. Results suggest that effectiveness of ecological classification systems as tools for landscape-scale management is enhanced whenthey include both spatial and temporal heterogeneity among ecosystem units.