Vegetation-environment relationships of forest ecosystems in the unglaciated Allegheny Plateau of southern Ohio

Background/Question/Methods

Understanding the underlying factors that regulate vegetation distribution across diverse environmental gradients is important not only to advance understanding of ecological principles, but also in the application of restoration and management decisions. The goal of this research project was to quantify the vegetation-environment relationships in the Ironton Unit of Wayne National Forest, located in the highly dissected landscape of the Southern Unglaciated Allegheny Plateau of southern Ohio. Specifically, we explored the following questions: 1) Which environmental factors have the greatest influence on species distribution in the canopy and herbaceous ground flora layers? and 2) What are the differences in species richness and diversity along these gradients? Study plots were located within mature stands with trees at least 70 years old and no evidence of anthropogenic disturbance within the last 40 years. Initial exploratory analyses using Detrended Canonical Correspondence Analysis (DCCA) suggested that a linear analysis would be most appropriate; consequently, we used redundancy analyses (RDA) to ordinate species and environmental factors for the canopy and for the ground flora. Of the environmental variables measured, only factors selected as significant by Monte Carlo permutation procedures were included in analyses. Once the most influential environmental drivers were identified, we calculated species richness and diversity indices for three aspect groups (northeast, southwest, neutral) to characterize the forest communities along species gradients.

Results/Conclusions

In both the canopy and ground flora, physiographic variables including aspect and distance from the ridgetop were highly correlated with species occurrence in this southern Ohio forest landscape. In particular, chestnut oak (Quercus prinus) and black oak (Quercus velutina) were associated with ridgetops, while yellow-poplar (Liriodendron tulipifera) dominated the lower slopes. Northern red oak (Q. rubra), green ash (Fraxinus pennsylvanica), and sugar maple (Acer saccharum) were all associated with northeasterly aspects. White oak (Q. alba) tended to dominate southerly slopes and was correlated to soil variables including thicker B horizons and higher cation exchange capacity. Soil variables including pH, calcium and thickness of the B horizon were also strongly correlated with herbaceous species distribution. Northeasterly slopes, which tend to be more mesic, had the highest species richness and diversity, both for the canopy and the ground flora. Our results suggest strong, predictive relationships between vegetation and environmental factors, and they provide valuable reference condition information useful for the restoration of forest ecosystems in the Unglaciated Allegheny Plateau.