Dendrochronology of two butternut (Juglans cinerea) populations in the southeastern United States
Butternut (Juglans cinerea) has been an important component of eastern hardwood forests in North America since the last ice-age, but an exotic fungal pathogen (Sirococcus clavigignenti-juglandacearum) has been devastating the species throughout its native range since the late 1960s. Restoration strategies have not been widely adopted in the southern part of the species’ range, in part due to lack of information on disease and stand dynamics in the region.We initiated a study in 2004 to determine the feasibility of using butternut in tree ring analysis and to determine effects of climate and competition on growth and mortality of butternut trees. We studied the tree ring characteristics and population dynamics of butternut populations in southwestern Virginia and in central Tennessee. Butternuts in both populations were found to be relatively sensitive to annual variation of climate, particularly Palmer Drought Severity Indices, and had easily distinguishable tree ring boundaries. Overstory tree competition appeared to be accelerating butternut decline in a stand originating from a clearcut, while old-field succession was benefiting a butternut population in another stand. Our results indicate that potential exists to use dendrochronology as a tool in understanding the dynamics between butternut canker disease, exogenous factors (climate, disturbance), and endogenous factors (tree age, genetics) that will affect butternut population restoration efforts. These results should be tested in other parts of the species’ range.