Gradient analysis of the distribution of a fungal disease of Cornus florida in the southern Appalachian Mountains, Tennessee

Based on 115 samples collected throughout the western portion of Great Smoky Mountains National Park, southern Appalachian Mts., and on spatial data derived in a GIS (Geographical Information System), the distribution of the disease dogwood anthracnose affecting Cornus florida (flowering dogwood), caused by the fungus Discula destructiva in this portion of the Park was assessed, and factors contributing to the disease's severity were identified through correlation and multiple linear regression analysis. The degree of infection varies considerably locally, and is influenced by elevation, slope curvature, slope position, and potential soil moisture. However, the abundance of C. florida (stem density) alone explains 25 % of the variation in disease severity. Factors contributing to disease severity do not change significantly between disturbed and undisturbed sites. The highest mortality rates are restricted to dense stands in damp, sheltered sites at low slope positions, implying that surviving populations of flowering dogwood may represent a biased genetic subset of the original population.