Constraints on the assembly of cliff communities at the seed bank stage

Seed banks on cliffs of the Niagara Escarpment, southern Ontario, Canada, were examined and compared to different, but immediately adjacent, communities on plateaus and talus slopes to evaluate the role of the seed bank in controlling the mature vegetation of cliff-face communities. Soil samples were collected five times at two sites over three years. Data were analyzed three ways: multiple discriminant analysis on community composition, univariate ANOVAs of seed density data, and analysis of seed characteristics. The emergence of constraints on final plant community structure was clearest for the discriminant analysis: year of collection separated the seed bank centroids the most, but a secondary effect we observed was the clear separation of the three community types and their association with species found in their specific mature communities. ANOVAs and the analyses of seed characteristics did not show statistically significant community-related sorting. Although the cliff-face community structure was discriminated at the seed bank stage, it was not directly correlated with the above-ground vegetation; therefore subsequent processes such as seed germination and seedling survivorship must also be responsible for final community composition.