IMPACTS OF DROUGHT ON TREE MORTALITY AND GROWTH IN A MIXED HARDWOOD FOREST

The tree and shrub species on a 16-ha watershed in the Coweeta Basin w ere sampled in 1984 and again in 1991 to determine the effects of drou ght on tree species composition and basal area growth. Mortality and r adial growth were determined for tree species within three community t ypes that represent a moisture gradient from moist to dry: cove-hardwo ods > mixed-oak > oak-pine. Tree mortality from 1984 to 1991 was 20 % and 23 % in the cove-hardwoods and mixed-oak communities, respectively , compared to only 12 % in the oak-pine type. With the exception of Ox ydendrum arboreum and Robinia pseudoacacia, the oaks had higher percen tage mortality than any other genus; Quercus velutina had 29 %, 37 %, and 20 % mortality in the cove-hardwoods, mixed-oak, and oak-pine type s, respectively; Quercus prinus had 23 % mortality in the mixed-oak ty pe; Quercus coccinea had 36 % mortality in the mixed-oak type; and Que rcus marilandica had 27 % mortality in the oak-pine type. Mortality oc curred mostly in the small-size class individuals (< 10 cm in diameter ) for all species, suggesting that thinning was still an important pro cess contributing to mortality 29 yr after clearcutting. Although grow th of Liriodendron tulipifera was much higher than growth of either Qu ercus prinus or Quercus coccinea, growth in Liriodendron was significa ntly reduced by the 1985-88 drought and no growth reduction was observ ed for these two dominant Quercus species during the same time period.