Successional and structural responses to overstorey disturbance in managed and unmanaged forests

Abstract

We examined the effects of partial harvesting on the successional and structural development of forest stands relative to an unmanaged relict stand in Quercus-dominated forests in Indiana, USA over an 84-year period. Despite abundant ingrowth of shade-tolerant Acer and Ulmus species into the understorey of all stands, the double-harvest stand exhibited greater increases in richness, diversity and species mingling among strata relative to the relict stand. The release of mid-tolerant genera, Carya and Fraxinus, through overstorey disturbance, resulted in species composition more akin to earlier stages of stand development. Within the relict forest individuals from mid-tolerant species became more aggregated over time, but in the double-harvest stand they became less aggregated. Differences between stands were related to the degree of overstorey disturbance; from the relict, to the double-harvest stand, we observed consistent patterns among multiple measures. Retrogression of stand succession was evident based on stand structure over time and functional resilience to overstorey disturbance was reflected in mid-seral, mast-producing species composition. This study highlights the long-term influence of understorey vegetation on stand compositional and structural development, and the potential to achieve greater diversity in forest composition and structure in forest ecosystems prone to species homogenization due to lack of disturbance.