Wildfire effects on plant species richness at multiple spatial scales in forest communities of the southern Appalachians

1 We fitted species-area curves to the power function and examined changes in the parameters to quantify changes in species richness of all plants together, trees only and non-trees over five scales of magnitude (0.01 m(2) to 400 m(2)) after a wildfire in the Linville Gorge Wilderness Area, North Carolina, USA. 2 Increases in species richness of all plants together occurred after the fire at all scales and increased in magnitude as scale increased. However, a lack of change in the slopes (z-values) of species-area curves indicates that proportional changes were independent of scale of observation below 400 m(2). Changes in species richness were predominantly driven by immigration, which was significantly related to fire severity. Survival of species present pre-fire was greater than local extinction, but neither was related to severity. 3 Species richness of trees increased at all scales but proportional increases were smaller at larger scales and slopes of species-area curves decreased after the fire. Local seedling recruitment increased species richness at small scales, but low rates of immigration due to dispersal limitation in most species limited increases at larger scales. 4 Directional changes in species richness of non-trees were not always consistent at fine scales but both absolute and relative changes were positive at scales >= 1 m(2) and increased with increasing scale. Slopes of species-area curves increased post-fire because localized patterns of immigration within plots resulted in little mixing of species at small scales but large changes in species richness at larger scales. 5 Fire in the southern Appalachians increases plant species richness within local communities, but rates of species turnover and patterns of beta diversity are maintained by local recruitment of tree seedlings at small scales and immigration of herb, shrub and vine species at larger scales. 6 Although decreased levels of competition after disturbance promote species coexistence at small scales, changes in species richness at larger scales are determined by the degree that the local community is linked to the species pool of the surrounding landscape through processes related to dispersal, particularly mass effects.