Decline of <Emphasis Type="Italic">Cornus florida</Emphasis> and forest succession in a <Emphasis Type="Italic">Quercus–Carya</Emphasis> forest

Cornus florida is a common understory species in many hardwood forests in eastern North America. It plays an important role in nutrient cycling and is an important food resource for many vertebrate species, especially migratory birds. We used data collected over a 16-year period to examine population dynamics of a tagged population of C. florida in a 6.4 ha area in the context of change in the protected Quercus–Carya forest of the Ross Biological Reserve, Indiana. We examined the hypothesis that forest dynamics result from interactions between long-term ecological succession and pathogens. The C. florida population at the Ross Reserve declined by 50% between 1983 and 2000, with a survivorship of 24%. Analysis of 40 years of forest survey data showed that Quercus and Carya populations declined in importance, while Acer saccharum increased dramatically. This change in forest structure is consistent with successional changes occurring throughout the Midwest and can be attributed to suppression of disturbance. Cornus florida declined more sharply where A. saccharum increased. From 1983 to 1999, C. florida were less likely to survive if they were within 5 m of a A. saccharum. Light measurements showed that A. saccharum abundance correlated negatively with light available to C. florida, suggesting that increased shading by A. saccharum contributed to C. florida decline. The fungus, Discula destructiva causes the disease dogwood anthracnose that is associated with widespread decline of C. florida in the eastern United States. Tests for this pathogen in our study area were mostly negative. Other tests revealed that Armillaria root rot infected most C. florida, but this disease seemed to be a secondary effect of shading by A. saccharum. These results suggest that the lack of fire and other anthropogenic disturbances has resulted in an accelerated shift in dominance from Quercus and Carya to A. saccharum in the main canopy, and this shift, in turn, has resulted in increased shading of C. florida and its decline in previously more open Midwestern forests.