Effects of silvicultural disturbance on diversity, species composition, and soil resource availability in Appalachian forests

The long-term effects of land management and altered disturbance regimes on diversity and function of forest communities are difficult to predict, because few studies exist that apply disturbance in a replicated design and control for differences among sites. Past studies of silvicultural disturbance treatments have shown increases or decreases in native plant diversity, increases in invasions by non-native species, and either increases or decreases in soil resource availability. We have been investigating how five silvicultural disturbance regimes influence native and non-native diversity, species composition, and soil properties (a potential controlling factor of native diversity and invasion) in the southern Appalachian Mountains. A gradient of timber harvesting intensity was established and replicated at seven sites in Virginia and West Virginia in the mid-1990s including un-disturbed control, understory herbicide (14% of basal area removed), shelterwood harvest (56% removed), leave tree harvest (74% removed), and clearcut (95% removed). Diversity of both native and non-native species increased in all treatments one year after disturbance through colonization of mostly ruderal species. Species richness tended to decrease slightly 12 years following disturbance but still remained higher than pre-disturbance levels. Soil organic matter (OM) and nutrients correlated with OM (e.g., NH₄, Ca) were greater in more disturbed plots 12 years following disturbance. Changes in community composition occurred immediately following disturbance but were less pronounced 12 years after disturbance and depended on site factors (e.g., soil type). These results suggest that timber harvesting increases plant species diversity by increasing resource availability, which allows both native and non-native species to invade sites. We will continue to monitor these plots to investigate non-native species persistence, compositional trends, and the long-term response of soil resource availability.