Structure and short-term dynamics of the tree component of a mature pine-oak forest in southeastern Arkansas

SHELTON, M. Cl. AND M. D. CAIN (USDA Forest Service, Southern Research Station, Monticello, AR 716563516). Structure and short-term dynamics of the tree component of a mature pine-oak forest in southeastern Arkansas. J. Torrey Bot. Sot. 126:32-48. 1999.-The R.R. Reynolds Research Natural Area is a 32.ha secondgrowth forest with little human intervention for nearly 60 years. In this paper, we characterize the existing vegetation, which represents 60 years of successional change with no major disturbances, and report vegetative changes over a 5-year period, which suggest the future successional direction. Trees 2 9.0 cm DBH were inventoried in twenty 0.1.ha plots and placed into four species groups: pines, oaks, other overstory trees, and midstory trees. Loblolly pine (Pinus taeda L.) was the dominant tree species, accounting for 51% of the total basal area and having the largest mean DBH (56.5 cm) and height (35.7 m). Tree ages ranged from 50 to 140 years for the pines and from 40 to 150 years for the oaks. However, 70% of the pines became established in the 4 decades that followed harvest of the virgin forest in the 1910s while the oaks showed two peaks of establishment (one after harvest and one 50 years before harvest). The pines displayed a bell-shaped DBH-class distribution, while the oaks displayed a gradual decline in numbers as DBH-class increased. In contrast, the other overstory trees and midstory trees had negative exponential distributions. Multiple occupancy was common within the canopy, which had a horizontal coverage of 97%. Canopy positions of the species groups were as follows: pines>oaks>other overstory trees>midstory trees. The growth of individual trees was positively related with tree size. Stand-level survivor growth was positively related with the basal area of the species group. Recruitment was greatest for the other overstory trees and midstory trees (totaling 6.2 trees ha-’ yr-‘), but did not occur for the pines and oaks. Mortality of large pines during the observation period (averaging 3.3 trees ha ’ yr’) resulted in net losses in basal area and volume for that species group. By contrast, hardwood species groups displayed net increases, totaling 0.17 mz haa yr ’ for basal area and 1.59 m’ ha ’ yr’ for volume. Stand dynamics suggest that the shade-intolerant pines are rapidly being replaced by more shade-tolerant hardwoods.