CANOPY GAP CHARACTERISTICS AND DROUGHT INFLUENCES IN OAK FORESTS OF THE COWEETA BASIN

Canopy gaps in southern Appalachian mixed-Quercus forests were charact erized to assess the impact of the 1985-1988 record drought on pattern s of tree mortality in relation to topographic variables and changes i n overstory composition. Using permanent transects, we sampled 68 cano py gaps within the Coweeta Basin. Among 1-5 yr old gaps, the most comm on gap type was the 1-yr-old single-tree snag, accounting for 49% of a ll gaps sampled; 65% of all gaps occurred within 2 yr of the drought p eak. 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 yielde d a gap formation rate of 0.8 gaps . ha-1 . yr-1 in mixed-Quercus stan ds affecting 2.0% of the area in this forest type in 1988. The most fr equent gap-forming species were Quercus coccinea, Q. rubra, and Q. vel utina, 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 signific ant shifts in canopy composition in these forests.