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

The R.R. Reynolds Research Natural Area is a 32-ha second growth forest wit h little human intervention for nearly 60 years. In this paper, we characte rize the existing vegetation, which represents 60 years of successional cha nge with no major disturbances, and report vegetative changes over a 5-year period, which suggest the future successional direction. Trees greater tha n or equal to 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, accou nting 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 pin es 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 harv est and one 50 years before harvest). The pines displayed a hell-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 commo n within the canopy, which had a horizontal coverage of 97%. Canopy positio ns 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 basa l area of the species group. Recruitment was greatest for the other oversto ry trees and midstory trees (totaling 6.2 trees ha(-1) yr(-1)), but did not occur for the pines and oaks. Mortality of large pines during the observat ion period (averaging 3.3 trees ha(-1) yr(-1)) resulted in net losses in ba sal area and volume for that species group. By contrast, hardwood species g roups displayed net increases, totaling 0.17 m(2) ha(-1) yr(-1) for basal a rea and 1.59 m(3) ha(-1) yr(-1) for volume. Stand dynamics suggest that the shade-intolerant pines are rapidly being replaced by more shade-tolerant h ardwoods.