Factors maintaining a disjunct community of Liatris spicata and other prairie species in Ontario, Canada

Abstract

Plants of the prairie peninsula have persisted in southwestern Ontario in localized areas where a high water table in spring, severe drought in midsummer, and intermittent burning have limited forest encroachment. Unlike these relicts of the postglacial xerothermic period, a community of prairie species on a railway embankment at West Hill (Toronto) has developed within the last 100 years. It is postulated that the persistence of these prairie species in the face of intense competition by seedlings from the surrounding fields is due largely to their adaptation to the seasonal fluctuation of moisture availability, nutrient deficiency, and periodic disturbance at this site. Mortality of invading seedlings was due to extrinsic environmental stresses rather than competition for limited resources during the period of active growth. The perennial Liatris spicata was able to dominate part of the habitat as a result of rapid growth of adults and seedlings before drought, low requirement for nutrients and effective mobilization from the corm in spring, and resorption before senescence. Experimental trials suggest that accumulation of litter, improving the moisture-retention and nutrient availability of the substrate, will lead eventually to elimination of Liatris and the other disjunct species. The case for preserving this community and other wet-mesic prairies in southwestern Ontario is outlined. However, it is clear that the current practice of 'conservation by complete protection' should be replaced by a management policy of periodic burning or mowing.