Print PageForests growing on abandoned agricultural lands may show the effects of their agricultural heritage for hundreds and even thousands of years. Some of the strongest and most lasting legacies of past agriculture are changes in the diversity and composition of herbaceous plant communities. Here I review these changes and examine the mechanisms underlying them, paying particular attention to the evidence supporting the mechanisms of dispersal limitation and environmental sorting. I illustrate the patterns and processes of herbaceous plant community responses to agriculture with case studies from forests in central New York state.
Results/Conclusions
It is abundantly clear that agricultural land use has a strong and lasting influence on plant diversity and distributions. One of the most consistent changes in herbaceous plant communities is a reduction in the species richness of native forest species. This pattern is supported by data from central New York state. Changes in species composition are also common; an ordination of data from central New York state illustrates specific examples of shifts in species composition due to past agriculture. Several lines of evidence indicate that dispersal limitation is partly responsible for these patterns. For example, species richness increases with post-agricultural forest age and decreases with isolation in central New York state and many other regions. However, attempts to relate species distributions to dispersal traits have produced equivocal results. Recently, more attention has focused on the role of environmental sorting as a potential driver of the recovery process in post-agricultural plant communities. In central New York state as well as other regions, certain forest herb species show differential performance in post-agricultural forests compared to forests that were never cleared for agriculture. Seed-sowing and transplant experiments have produced a variety of results, with some species performing equally well in post-agricultural and never-cleared forests, and some species showing an apparent preference for one forest type or the other. Interesting results have also been emerging from studies of population dynamics and community interactions in post-agricultural forests. We are close to articulating generalizations about the process of herbaceous community development in post-agricultural forests that will not only advance ecological understanding, but also contribute to efforts to conserve and restore biodiversity in these communities.
