Temporal and spatial variation in abundance of Allium tricoccum (Liliaceae) in the Southern Appalachians.
Walker, Joan*,1, Silletti, Andrea 1, White, David1, 1 USDA Forest Service - Southern Research Station, Clemson, SC, USA
ABSTRACT- Allium tricoccum, known as wild leek or ramps, is a culturally important herb harvested by digging in the early spring. Population declines attributed to over-harvesting in its northern range have led to concerns about the status of A. tricoccum in the southeast. In 1999, we randomly selected 21 relatively high-density plots (>20 ramets/m2), presumably attractive to harvesters, in the Upper Nantahala River watershed. Annually (1999-2005), we quantified leek density and cover, and soil disturbance along permanent transects. We described plot environmental variables and vegetation, and examined local temperature and precipitation data. We address the following questions: Does abundance differ among plots and through time? How does abundance vary with site quality? Does disturbance affect mean density and temporal variability? We used analysis of variance methods with repeated measures to detect differences among plots and through time, and regression analyses to examine relationships among abundance and environmental variables. Abundance was significantly predicted by aspect (p=.0004, r2 = 0.365), increasing from west through north and east. About half of the plots showed significant differences between at least two years. Based on this result we defined two groups, changers and non-changers, and used discriminant function analysis to model membership in the groups. Elevation alone correctly classified 75% of the plots as changers or non-changers. Plots that changed were located at the lowest elevations (1200 m); higher elevation plots did not vary during the study. The largest changes were negative (Chi-square test; p< .05) and occurred between 2000 and 2001, coincident with severe drought conditions in the region. Results confirm that seasonal weather extremes may affect abundance from year to year, especially at lower elevations. Based on the frequency of disturbance in 1-meter segments along transects, we classed plots as disturbed or non-disturbed. Compared to undisturbed plots, the disturbed group had significantly lower densities, but the groups did not perform differently through time. Although sites with the most soil disturbance are likely to have lower Allium densities, populations appear stable under current harvest pressure.
Key words: Allium tricoccum, Southern Appalachians, harvest disturbance, climate
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