Natural recovery and restoration potential of severely disturbed talus vegetation at Niagara Falls: Assessment using a reference system

The talus slope adjacent to the Niagara River at Niagara Falls (Ontario, Ca nada) has been severely disturbed over the course of the past century as th e area has been increasingly developed for tourism. In addition the lower t alus slope is disturbed by periodic ice scour, most recently one year prior to this study. Historical evidence suggests that the original vegetation w as similar to that currently found on talus slopes of the Niagara Escarpmen t, which could, therefore, be used as a reference system and restoration ta rget. The current community structure and physical environment were sampled in 75 randomly placed 1-x-1-m quadrats. A total of 137 species were found, of which 62% were aliens. ANOVA showed that species richness, woody debris cover, litter cover, soil depth, and photosynthetically active radiation c hanged along a gradient perpendicular to the river. Three different section s of the study area whose last severe disturbance dated back 100, 30, and 4 years, respectively, were similar in their physical environment but were s ignificantly different in species richness. Ordinations of species frequenc ies showed that light levels and distance from the river were the principal gradients controlling the vegetation structure. The species composition of the section last disturbed 100 years ago was different from that of the mo re recently disturbed sections. Ordination and cluster analysis of the pool ed data showed large differences between the Niagara Falls site and referen ce escarpment talus slopes. Natural escarpment vegetation was much more hom ogeneous and had more species and fewer aliens. By comparing reference talu s with sections of the study area at Niagara Falls that were last disturbed at different times, we conclude that the trajectory of natural succession at Niagara Falls is leading to an alternative state, an urban forest domina ted by aliens, and that active restoration will be required to return the t alus to its original state.