Effects of natural habitat fragmentation on the species richness, diversity, and composition of cliff vegetation

Plant species richness, diversity, and some aspects of species composition were measured on natural limestone cliff fragments of varying size within t he Niagara Escarpment Biosphere Reserve, Canada. This information was colle cted because knowledge about how different components of community structur e change in response to natural fragmentation may permit the prediction of the effects of future anthropogenic fragmentation. The number and relative abundance of vascular plant, bryophyte, and lichen species were determined on cliff fragments that varied in area from 185 to 126 000 m(2). Latitude, aspect, percent available photosynthetically active radiation on the cliff face, distance from the nearest neighbouring cliff, and length of the neare st neighbouring cliff were also measured. Regression analysis was used to t est for a significant relationship between fragment area and diversity of v ascular plants, bryophytes, and lichens both separately and combined. Multi ple regression with all subsets selection was used to find the best predict ors of species richness from among all variables measured for the 21 cliff fragments. Multivariate analyses were used to study the effect of fragmenta tion on the structure of the vegetation as a whole. The results showed no s ignificant relationship between cliff fragment area and richness or diversi ty for vascular plants and bryophytes, and only a marginally significant in crease in richness with area for lichens. The multivariate analyses also sh owed that only one community type exists, and that its structure mainly var ies as a function of latitude. These results indicate that very small fragm ents of cliff face can support a similar plant biodiversity as do large con tinuous portions of the Niagara Escarpment.