Canopy Gap Characteristics and Drought Influences in Oak Forests of the Coweeta Basin
Canopy gaps in southern Appalachian mixed-Quercus forests were characterized to assess the impact of the 1985-l988 record drought on patterns of tree mortality in relation to topographic variables and changes in overstory composition. Using permanent transects, we sampled 68 canopy gaps within the Coweeta Basin. Among l-5 yr old gaps, the most common gap type was the 1-yr-old single-tree snag, accounting for 49% of all gaps sampled; 65% of all gaps occurred within 2 yr of the drought peak. Gap area ranged from 40 to 850 m2, averaged 239 m2, with a median of 152 m2. Analysis of 1988 color infrared (IR) aerial imagery yielded a gap formation rate of 0.8 gaps ha-1yr-1 in mixed-Quercus stands affecting 2.00/o of the area in this forest type in 1988. The most frequent gap-forming species were Quercus coccinea, Q. rubra, and Q. velutina, respectively. Evidence suggests that moisture stress brought on by severe drought increases the susceptibility of Quercus species to the shoe-string fungus Armillaria mellea, which may result in significant shifts in canopy composition in these forests.