Convergence in Plant Community Structure Along Disparate Gradients: Are Lakeshores Inverted Mountainsides?

There is a growing consensus that relatively few factors with broad applicability underlie changes in the structure of different plant communities along different environmental gradients. Direct comparisons of variation in community structure with respect to common abiotic factors along different environmental gradients would provide a test of this hypothesis. We illustrate this by quantifying patterns of species diversity and growth form along two gradi- ents, a lakeshore and a mountainside. On both gradients, standing crop increased with productiv- ity; light at the soil surface and bare ground decreased. The proportions of woody species, stemmed species, phanerophytes, and chamaephytes increased with productivity, whereas hemicryptophytes decreased. Regressions of species diversity and growth forms on number of growing days, for both gradients simultaneously, allowed each variable to be described by the same regression formula for both gradients, even though the lakeshore spanned 67 cm in altitude and the mountainside 495 m. These results demonstrate statistically significant vegetation- environment correlations in a range of state variables in spite of the fact that these two gradients appear fundamentally different.