Diversity can be maintained, at least in part, by conspecific inhibition, which is defined as a reduction in performance when conspecific density is high. For instance, if tree seedlings are inhibited near conspecific adults, other tree species will be more likely to regenerate, thereby facilitating local coexistence. Several mechanisms are responsible for conspecific inhibition, including species-specific insect pests and pathogens. To investigate conspecific inhibition in flowering dogwood (Cornus florida), we planted seedlings in central Virginia (in April 2018) at various distances from conspecific adults that spanned a range of sizes, and then visually assessed foliar damage (in August 2018). Foliar damage was quantified separately in each of the following categories: chewing, leaf spots/rust, mold/mildew, sucking/rasping, wilting, folding/rolling, other discoloration, and other foliar damage. We did not analyze growth and survival – in this first season of monitoring – because growth rates were extremely low (and nearly impossible to separate from measurement error) and survival rates were extremely high (nearly 100%). Damage was analyzed as a function of local mature conspecific abundance around each seedling, quantified as the inverse distance weighted basal area within a 10m radius.
Results/Conclusions
We found a significant positive correlation between abundance of mature dogwood trees and total foliar damage (summed across all categories) on developing dogwood seedlings. When analyzed further, we found a significant positive correlation between mature dogwood abundance and four separate individual damage categories: rasping/mining (p=.000005), mold/mildew (p=0.00423), other discoloration (p=.00452), and other foliar damage (p=.000246). Remarkably, these results point toward multiple distinct causes of seedling damage that encompass both insects and pathogens. Our results add to the rapidly accumulating body of evidence that conspecific inhibition is common in the forests of the eastern United States. While we cannot be certain that the pronounced foliar damage patterns we detected will translate to growth and survival, our findings suggest that conspecific inhibition (occurring via species-specific insect pests and/or pathogens) helps to prevent dogwood from dominating local areas.