Dynamics of diversity during succession in a deciduous forest

Background/Question/Methods Patterns of diversity through succession have been described in many systems, particularly in testing the intermediate disturbance hypothesis. However, to account for the long time scales involved, successional studies often utilize space for time substitutions. This methodology assumes that all sites will experience the same successional dynamics and that between-site variation is minimal. Continuous long term successional studies are uncommon but can alleviate the limitations of space for time substitutions and lead to more direct insights into community dynamics. This study utilized field data from the Buell-Small Succession Study, a long term study following succession from abandoned agricultural fields to deciduous forest. Fifty years of vegetation dynamics in permanent plots were used to examine patterns of diversity and community dynamics. We quantified measures of diversity across 10 replicated old fields to determine the dynamics of diversity through succession and to test for evidence of the intermediate disturbance hypothesis.

Results/Conclusions Rank-abundance curves indicated a change in species abundance distributions throughout succession with the curves becoming flatter as succession proceeded. The number of rare species increased significantly over time while the number of dominant species remained constant at around 4. Species richness at the field scale increased through succession, peaked at year 41 and began to decrease gradually. Shannon-Weiner diversity also showed evidence of a peak around the same time, showing support for the intermediate disturbance hypothesis. Evenness did not change significantly over time, suggesting that diversity changes were primarily driven by gains and losses of species. The decrease in diversity late in succession appears related to the transition of intermediate abundance species to rare species. As rare species are more likely to disappear from the community, a net loss in species richness occurred. We found evidence for the intermediate disturbance hypothesis that suggests diversity peaks within the first 50 years of succession in young deciduous forests. These data confirm the patterns of diversity seen in space for time substitution studies, indicating the robustness of those conclusions at the community scale.