The response of plant communities to human disturbance in southern Indiana forests

The overall objective of this study was to determine how past human disturbance has altered forest plant communities within three ecological land type phases (wet-mesic bottomlands, mesic slopes and dry-mesic slopes) in southern Indiana. Specific objectives were to (1) summarize how past land use has changed the land cover of the Charles C. Deam Wilderness in southern Indiana between 1939 and 1990, (2) determine how past disturbance (agriculture, clearcutting, group-selection harvest, and single-tree selection harvest) has altered herbaceous and woody vegetation in Platanus/Asarum wet-mesic bottomlands, (3) determine how silvicultural practices (clearcutting, group-selection harvest, and single-tree selection harvest) have altered herbaceous and woody vegetation on Fagus-Acer saccharum/Arisaema mesic slopes and Quercus alba-Acer sarccharum/Parthenocissus dry-mesic slopes, and (4) determine how silvicultural practices have influenced the volume of down deadwood. In 1939 land cover of the Charles C. Deam Wilderness was 33% agriculture/old-fields and 26% open/grazed forest. Closed canopy forest comprised only 41% of the total land area. By 1974, 78% of the Wilderness was closed canopy forest and by 1990 closed canopy forest comprised 86% of the landscape. This increase in closed canopy forest has drastically decreased forest fragmentation in the landscape. While closed canopy forest now dominates Hoosier National Forest, abandoned agricultural areas in wet-mesic bottomlands still exhibit highly disturbed understory plant communities with large components of exotic and disturbance species. In comparison, silvicultural practices have not altered understory species composition and diversity to the degree that past agriculture has. Past agricultural use, clearcutting, and group-selection harvest have created overstories dominated by Liriodendron tulipifera and other early successional species, while single-tree selection harvesting has accelerated succession towards dominance by Acer saccharum and reduced overstory species richness. Down deadwood volume was greatest in recent silvicultural openings and old-growth but declined in older openings and was lowest in 80-100 year-old stands. Overall, the results of this study suggest that large-scale disturbance is needed to maintain the structure and diversity of southern Indiana forests