Midwest oak savannas contain some of the highest plant diversity in the United States and are one of the rarest ecosystems left. In areas where historical oak savannas have remained, they have been degraded by the absence of fire. Understanding the structuring of their diversity is important for conservation and restoration. The purpose of this study was to understand the role of canopy cover and canopy heterogeneity in structuring plant diversity within these ecosystems, including beta diversity. This study took place in remnant and restored black oak savannas of the Indiana Dunes. Vegetation surveys took place in areas of varying canopy cover and heterogeneity, ranging from open to closed canopy.
Results/Conclusions
Total plant species richness and Shannon diversity indices were highest in plots with intermediate canopy cover (40-50%). Woody species richness and Shannon indices were highest in areas with a high canopy cover (>80%). C3, C4, and sedge species richness and Shannon’s indices were highest in areas with low canopy cover (<25%). Forb species richness and Shannon indices were highest with low to intermediate canopy cover (25-50%). Legume species richness and Shannon indices were highest with no canopy cover to intermediate (0-45%). There was no relationship between canopy cover or canopy heterogeneity (measured as variance) with beta diversity (community dissimilarity within sites). However, dissimilarity was exceptionally high within all sites with most Bray-Curtis values ranging from 0.7-0.9. This is remarkable considering some sites have been excluded from fire, a key component for heterogeneity, for 50 years. From a management perspective, an average canopy cover of 25-50% is the optimal cover for promoting high plant diversity across many functional groups.