- Butler, Sarah Marie
University of Maine Graduate School
Understanding the patterns of past disturbance allows further insight into the composition' structure, and function of today's forests. Disturbance history may also influence how forests will react to future stresses and disturbances. The disturbance histories of the mixed-oak forests at the coweeta Hydrologic Laboratory (a 2,1g5 ha long-term research site with some history of harvesting) and the Joyce Kilmer wilderness (a 6'805 ha old-growth forest with no known harvesting) located in southwestern North Carolina were studied using dendroecology. Dendroecology uses increment cores to determine tree ages and patterns of radial growth. In addition to evaluating the history of these two areas to better understand disturbance dynamic in the southern Appalachians, we compared the radial growth patterns of old-growth trees at Joyce Kilmer to remnant old-growth trees at coweeta to determine if the trees have similar responses to disturbances throughout time.
We found average decadal disturbance rates (calculated as percent of plot area affected per decade back to the mid-1700s) at coweeta and Joyce Kilmer (8.7% to 18.3%) were similar to rates common in eastern temperate forests (5% to 20%). The general disturbance history is one of low, but fluctuating, rates, indicating the importance of small canopy gaps in these forests. Among the typically low rates of disturbance present in all stands are occasional, and noticeably higher, peaks of disturbance.
The dominating peak in disturbance occurred across all stands in the 1920s and 1930s, likely attributable to American chestnut (castanea denîata(Marshall) Borkh.) mortality due to the chestnut blight. Logging created pulses of disturbance in the 1900s, 1910s, and 1920s. Natural disturbances, such as windthrow from hurricanes, drought, insect outbreaks, and ice storms likely contributed to both the peaks in disturbance across the stands (1840s and 1960s) as well as localized pulses unique to single stands.
Disturbance rates and patterns over time were not random with respect to species composition' The more closely related stands were in species composition, the more similar they were in disturbance history. This is likely due to some of the disturbances being specific to one or a few species. However, despite stands similar in species composition also being similar in elevation and slope, disturbance patterns were not influenced by elevation or slope.
The early harvests at coweeta were most likely selective, favoring some trees over others on the basis of species, size, or form. Thus, the remaining trees from that era were biased' making it unclear as to whether their growth patterns were representative of the pre-harvest disturbance history. Thus, we compared old remnant trees at coweeta to old-growth trees at Joyce Kilmer, asking if radial growth patterns from old trees surviving harvesting were comparable to those of trees growing in the same time period but free from harvesting. we found similar patterns in radial growth as well as similar disturbance histories, indicating that using remnant trees left behind after harvesting to determine disturbance histories is plausible, at least in these stands.