Invasibility of Differing Successional Stages of East-Central Indiana Forests by East Asian Shrubs

Indianapolis, IN

The introduction of exotic species to Indiana deciduous forests poses a serious threat to the biodiversity of native species. Previous investigations suggest that old growth forests may exhibit a resistance to invasive species. Recent proposals to log old growth stands to reintroduce shade-intolerant tree species preferable for timber and game could open previously closed canopies, allowing invasives to gain a foothold. We studied 8 different sites of varying successional stages (young, middle, and old growth) across 3 locations to examine the invasibility of these stands. We measured the light intensity in each site, and censused 4 invasive plant species: Amur Honeysuckle (Lonicera maackii), Multiflora Rose (Rosa multiflora), Japanese Barberry (Berberis thunbergii), and Autumn Olive (Elaeagnus umbellata), recording density and height for each. We also investigated the edge effects on L. maackii in an old growth stand. We found no significant difference in light intensity across successional stage or in height of 3 species of invasives; only the height of L. maackii was significantly different between stages. We found a significantly greater overall density of invasives in young growth stands when compared to middle or old growth. Our results indicate that although old growth stands are not immune to the colonization of exotic species, they do exhibit a greater resistance to invasion than young or middle growth. Our results suggest that the disturbance of an old growth stand could create opportunities for invasives to increase their rate of colonization and endanger the native biodiversity in East-central Indiana forests.