Forest Plant Composition in Patches of Varying Ages in an Intensively Farmed Landscape

Abstract

The stability of plant community diversity in post-agricultural forests is an important ecological question throughout the Midwestern United States. Since forests in this region are often islands in a matrix of annual croplands, a better understanding of the persistence of native plant diversity and the potential for incursions of exotic invasive species is crucial for maintaining biodiversity in these landscapes. This study examined plant communities in several post-agricultural forests in northern Indiana that varied by age since agricultural abandonment, and investigated differences in invasive species presence across several canopy layers (canopy, midstory, understory). Vegetation was sampled in circular plots across three distinct forest parcels. In addition to forest age, several other conditions hypothesized to affect plant diversity, such as tree canopy cover, litter depth, underlying soil type, and adjacent land uses, were also measured. Overall herbaceous diversity and integrity, as measured by the Floristic Quality Index (FQI), were relatively high in these forests. Invasive species, e.g., Alliaria petiolata and Rosa multiflora, were also generally uncommon in these forests, even in areas affected by local disturbances such as deer trails, trash dumps, and canopy gaps, although older plots generally had lower invasive presence than younger ones. This study highlights the importance of maintaining existing older-growth forests in this landscape and avoiding disturbances to the interior of such forests to minimize further expansion of invasive species.