The phytogeography of rare vascular plants in Ontario and its bearing on plant conservation

Abstract

The phytogeographic patterns displayed by the 550 rare vascular plant taxa in Ontario, including 349 that are rare nationally, are correlated with counties, site regions, and floristic provinces. Rare taxa are concentrated in southwestern Ontario decreasing northward, with secondary concentrations along the Hudson Bay coast. Rare taxa in Ontario are predominantly peripheral taxa, which have their main ranges outside of Ontario. Many of these taxa, however, have a high Canadian conservation priority because they are also at risk in adjacent states or provinces. Rare taxa with Appalachian and Coastal Plain affinities are most common in southwestern Ontario. Arctic and boreal affinities predominate in Northern Ontario. These patterns are correlated with temperature and moisture parameters, which are incorporated with the Hills' site regions classification. Most high conservation priority taxa occur in the Carolinian region, the most highly settled and most highly agriculturalized part of the province. There is an urgent need for conservation of the remaining forest and wetlands in this region. The fragmentary ecosystems still remaining must be protected from further development. There is a need to study the correlation of rare plant occurrences with existing parks and reserves throughout the province to facilitate the identification of priority regions for protection. Key words: rare plants, phytogeography, conservation, Ontario.