ATTRIBUTES OF RARITY AMONG ALBERTA MOSSES - PATTERNS AND PREDICTION OF SPECIES-DIVERSITY

Twenty-five percent (113 species) of the moss flora of Alberta is rare . Among these rare species, the pleurocarpous condition, presence of l ong-lived perennials, and competitive strategies are less common when compared with the complete flora. Rare species are over represented by the Bryales, Dicranales, and Funariales, while the Nypnales, Orthotri chales, and Sphagnales are under represented. Forty-two percent of the rare species have boreal distributions. The greatest occurrence of ra re species is in the Rocky Mountains, with numbers of rare species dec reasing southward. The largest proportion of rare species occur on soi l (57%) or rock (34%). We define habitat heterogeneity at two landscap e scales: the microhabitat scale and the mesohabitat scale, here defin ed as non-random sets of microhabitats. Rare species most frequently o ccur on cliff and alpine mesohabitats. In Alberta, 74% of the rare spe cies occurrences are on restricted mesohabitats (e.g., cliffs); the do minant mesohabitats (e.g., forests, grasslands) have fewer species. Th ese conclusions are important for management of rare species diversity Attributes of mesohabitats are useful in formulating predictions of r are species occurrence on. the regional landscape.