Background/Question/Methods One premise of equilibrium theory is that forest communities in, or approaching, equilibrium should show some degree of species convergence between resident overstory trees and advanced regeneration. Applying this theory to real data is often problematic because many communities have been highly disturbed and are not always easily partitioned into distinct, recognizable stages of succession. In addition, acceptable thresholds of convergence for different ecological communities have not been developed. To test for convergence, we used landscape-level data from the USDA Forest Service, Forest Inventory and Analysis (FIA) program. The 3,453,000-ha study area was situated on the Western Highland Rim (WHR) in western Kentucky, western Tennessee, and northwest Alabama. We identified 74 older stands with a minimum stand threshold of 30.0 cm quadratic mean diameter to use in the study. Convergence evaluations were done with a species-dominance ranking approach. Plots were categorized into 3 broad successional trajectories to evaluate and detect convergence: 1) maintaining the current population (convergence), 2) a reverse trajectory toward an earlier succesional stage, or 3) a forward trajectory toward a later successional stage.
Results/Conclusions The most common dominance-type forest communities in these older stands on the WHR were Quercus alba L. (20 plots), Q. prinus L. (12), Liriodendron tulipifera L. (11), and Q. velutina Lam. (6). Convergence was evident on only 15 percent of the Q. alba types, but present on 42 percent of the Q. prinus and 46 percent of the L. tulipifera types. In contrast, 20 percent of the Q. alba type showed a trajectory toward a later successional stage of more mesic species such as Fagus grandifolia Ehrh. and Acer saccharum Marsh. Likewise, 25 percent of the Q. prinus type and 27 percent of the L. tulipifera type showed a trajectory toward more mesic species. Specific ecological attributes of individual species complicate analysis. For example, although Q. alba showed less convergence, its long life (400-600 years) means there is adequate time for this type to maintain itself through some type of disturbance regime in the future (fire, gap phase replacement, etc.) Studies such as this are important in understanding the dynamics of vegetation change but convergence/trajectory analysis is hampered by the lack of adequate quantative techniques.