Relationships between forest health and plant diversity in western New York state forest lands (New York)

Forest health and sustainability have become matters of increasing concern throughout the world. Although many experimental studies suggest strong relationships among ecological health (stability), exotic species and diversity, there is limited evidence supporting this relationship in natural forest systems. I hypothesized that the complexity of natural forest systems might confound simple relationships between forest health and plant diversity. Through analyzing information collected at 160 randomly selected points in western New York state-owned forest lands, I examined the relationship among measures of plant diversity and forest health. My findings do not support the biodiversity-stability theory. Healthy stands, as defined by stands that fell within an expected baseline mortality (15–24% dead trees), did not have a higher tree species richness or diversity, understory richness or diversity, or total species richness or diversity. In fact, any differences between health levels were due to higher richness or diversity in the higher mortality stands (>24% dead trees). Exotic tree species richness is very low and the proportion of exotic tree species are equally distributed across all health levels. However, understory exotic richness is not equally distributed across all forest health levels, and a higher overall understory species richness may be over-represented in low mortality stands (<15% dead trees) due to exotic species compared to expected mortality stands. If forest health and diversity are important management goals at the stand level, they will have to be managed for separately. A “healthy” and “diverse” landscape will most likely need to include a mosaic of all health levels and forest classification categories to represent the full range of landscape plant diversity and forest health.