SPATIAL HETEROGENEITY OF VEGETATION AND ENVIRONMENTAL-FACTORS ON TALUS SLOPES OF THE NIAGARA ESCARPMENT

Spatial heterogeneity of vegetation and environmental factors were studied on talus slopes of the Niagara Escarpment, southern Ontario, Canada. Random sampling of 197 taxa and 19 environmental variables along the length of the Escarpment permitted multivariate analysis of heterogeneity that occurred at both geographical and local scales. While previous work on these slopes had indicated that rockfall disturbance was the main organizing factor of vegetation, this variable was shown to be unimportant. Instead, we found geographical-scale control of vegetation heterogeneity related to one component of macroclimate and local-scale heterogeneity controlled by a complex of soil factors. The local-scale heterogeneity appeared to be too patchy, however, to be explained by normal soil development processes. We suggest that the talus vegetation develops in response to a positive feedback mechanism involving inputs of slowly decomposing wood from the neighbouring cliffs, followed by accelerated vegetation development on patches of fertile organic matter.