Convergence during secondary forest succession.

Successional convergence in community composition was examined in terms of 3 questions: 1) for a given site is there a continuous shift in composition toward that characteristic of climax? 2) does variation in community composition along an environmental gradient increase or decrease with succession? 3) to what extent is the species composition along a successional gradient determined by site characteristics rather than by chance factors? Hypotheses regarding the nature of successional convergence were tested using data for tree and herb abundance from upland forest stands on the North Carolina piedmont which were grouped in five successional age classes. For each age-group first axis ordination scores (detrended correspondence analysis) were highly correlated most consistently with soil pH as compared with other soil and site variables. This correlation was greatest in the intermediate-age (40-60- and 60-80-yr-old) pines and in the hardwood stands, and lowest in old pine stands. Thus, there is a shift in species composition toward that characteristic of climax, but it is probably not monotonic. Beta-diversity was highest in the hardwoods and lowest among the pines. Community differentiation along gradients increased in this chronosequence. Habitat breadth in relation to soil pH decreased steadily with successional age. Results are consistent with the hypothesis that the role of chance factors decreases with successional age. -from Authors

Duke Scholars

Author Norman L. Christensen Environmental Sciences and Policy