Assessing Understory Vegetation Communities as Indicators of Ecological Integrity in the Toronto Ravine System

Abstract

Urbanization has resulted in the disturbance and loss of ecosystems around the globe. As this trend is unlikely to stop, it is essential for urban planning to adopt ecological concepts in order to increase the sustainability of urban centres. One of the first steps required for this to happen is the implementation of ecological monitoring within urban areas – this would allow a better understanding of the current ecological state of urban environments, from which future studies and management recommendations can be based on. The concept of ecological integrity, which aims to quantify the wholeness of an ecosystem’s structure, composition, and function, can be used as a guiding principle for such monitoring schemes. In this study, the ecological integrity of the urban ravine system in Toronto, Ontario is quantified using understory vegetation communities as an indicator group. Vegetation sampling sites were established in three ravines located in downtown Toronto, with plot selection based on a 1977 study of the same ravines. Each plot was then ranked as having low, medium, or high ecological integrity based on the proportion of native versus non-native ground cover in each plot. Additionally, two possible drivers of these patterns in ecological integrity were tested – the role of plot position along a slope, and the effect of non-native ground cover abundance. It was found that while invasive species dominated most plots, pockets of native vegetation were persisting within the ravines. Additionally, the majority of invasive ground cover appeared to be “leaking” down from residential areas at the tops of ravines, indicating the role of “garden escapes” as propagules for invasive establishment. Management recommendations include the implementation of citizen science programs to monitor the state of these vegetation communities, as well as using the information gathered to target their efforts.