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

Spatial heterogeneity of vegetation and environmental factors were stu died on talus slopes of the Niagara Escarpment, southern Ontario, Cana da. Random sampling of 197 taxa and 19 environmental variables along t he length of the Escarpment permitted multivariate analysis of heterog eneity that occurred at both geographical and local scales. While prev ious work on these slopes had indicated that rockfall disturbance was the main organizing factor of vegetation, this variable was shown to b e unimportant. Instead, we found geographical-scale control of vegetat ion heterogeneity related to one component of macroclimate and local-s cale heterogeneity controlled by a complex of soil factors. The local- scale heterogeneity appeared to be too patchy, however, to be explaine d by normal soil development processes. We suggest that the talus vege tation develops in response to a positive feedback mechanism involving inputs of slowly decomposing wood from the neighbouring cliffs, follo wed by accelerated vegetation development on patches of fertile organi c matter.