How disturbance has helped reduce the impacts of an exotic fungus in eastern hardwood forests

Background/Question/Methods

The impact of exotic pathogens on native plant species in North America over the past century has been profound. Often times, these pathogens are difficult to control across large forested areas and are capable of virtually eliminating the entire population of the affected species because of lack of resistance to the exotic pathogen. The objective of this study was to compare the impacts of dogwood anthracnose, a disease caused by the exotic fungus Discula destructiva, on Cornus florida populations in burned and unburned oak-hickory forests in Great Smoky Mountains National Park, US. Although anthracnose has decimated populations of C. florida across the eastern US, we hypothesized that in areas where fire has occurred, stand structure has been altered to create open conditions less conducive to the persistence and spread of the fungus. We compared C. florida density and health among four sampling categories: unburned stands, and stands that had burned once, twice, and 3 times over a 20-year period (late 1960s to late 1980s). Results/Conclusions

Double burn stands contained the greatest density of C. florida stems (770 stems ha^-1) followed by triple burn stands (233 stems ha^-1), single burn stands (225 stems ha^-1) and unburned stands (70 stems ha^-1; P < 0.01). We observed less crown dieback in small C. florida trees (<5 cm diameter at breast height) in burned stands than in unburned stands (P < 0.05). Our results suggest that fire has reduced the impacts of dogwood anthracnose in burned areas and may potentially be used as a tool by land managers to reduce the impacts of dogwood anthracnose in other areas, particularly those that are currently unaffected or lightly affected with the disease.