Forest dynamics of two multi-aged hemlock-mixed mesophytic forests in the northern Cumberland Plateau, Kentucky.

摘要

Tsuga canadensis (eastern hemlock) is a foundation species that performs a unique ecological role within the Appalachian mixed mesophytic forest of the eastern United States. However, the non-native hemlock woolly adelgid (HWA; Adelges tsugae Annand), a novel invasive colonizer, is significantly altering the natural processes within T. canadensis ecosystems. Few studies have documented T. canadensis forests before, during, and after HWA infestation. This study documented the pre-HWA conditions of two old hemlock-mixed mesophytic forests in eastern Kentucky by examining the composition, T. canadensis crown health, stand structure, age structure, and disturbance history. Rock Creek Research Natural Area (RCRNA) is a multi-aged primary forest while the Cold Hill Area (CHA) is a multi-aged mature secondary forest. Age structure and recruitment patterns at the RCRNA gorge imply limited, selective cutting at one end with old-growth forest conditions throughout the majority of the study area. In contrast, CHA appears to have experienced more intense selective cutting throughout a greater proportion of the study area. Larger synchronous disturbance peaks occurred in the decades of 1900 and 1980 and appear to be the result of logging in the early 1900s and, potentially, a combination of drought and windstorms in the 1980s. The most dominant canopy species at both study sites was T. canadensis, followed by Liriodendron tulipifera (tulip poplar). Like many forests across the eastern United States, Acer rubrum (red maple) had the greatest seedling density at both study sites. Nearly all T. canadensis trees were healthy with no visible signs of HWA. The disturbance history, tree recruitment, and pre-HWA data from this study provides important baseline information for comparing the future dynamics of Kentucky's Appalachian mixed mesophytic forest and other hemlock-dominated forests as HWA continues to significantly disrupt ecosystem processes.