Stand structural complexity enhancement is an increasingly popular management objective, especially on public lands. Complex stand structures are hypothesized to support a relatively high degree of native forest diversity and be more resistant and resilient to disturbances. Complex structures are characterized by the presence of deadwood and heterogeneity of tree size classes and tree architecture. Relatively little is known about how discrete disturbance events affect structural complexity and compositional diversity in Quercus-dominated stands at fine spatial scales (i.e. neighborhoods). We collected data in a stand on the Sipsey Wilderness of William B. Bankhead National Forest in northern Alabama. We established 20 0.05 hectare fixed- radius plots to quantify live tree species composition and structure, and measured coarse woody debris. Trees were mapped on each plot to quantify overstory structural complexity and compositional diversity. We extracted two cores from all canopy Quercus spp. ≥ 10 cm diameter at breast height (dbh) to quantify age, recruitment pulses, and reconstruct canopy disturbance history.
Results/Conclusions
Shannon diversity in the sampled area was 1.75 for trees, 2.08 for saplings, and 1.69 for seedlings. Quercus alba had the greatest basal area, and Ostrya virginiana had the highest density. The stand exhibited a reverse J-shaped distribution with a q-factor of 1.72. The oldest Quercus dated to 1795, and the largest recruitment pulse occurred in the 1870s. The mean return interval for stand-wide disturbance was 38 years. Although we documented no relationships between disturbance frequency and compositional diversity at the neighborhood scale (0.05 hectare), less frequent disturbance was associated with higher structural complexity (r2 = 0.258 p = 0.026) at this spatial scale. We suggest that localized disturbance increases species diversity and structural complexity, but these processes are manifest at the stand level and not at the neighborhood level. We conclude that the spatial variability (i.e. size, shape, orientation, microsite conditions) is likely more influential on diversity and complexity than the temporal variation (frequency) of these processes at a fine spatial scale.