Rarity at range limits; dispersal capacity and habitat relationships of extraneous moss species in a boreal Canadian National Park

Abstract

Rare moss species occurring in Terra Nova National Park, a boreal reserve in eastern Newfoundland, are extraneous members of the flora belonging to either temperate, arctic-montane, or montane elements. All are at or near their range limits. Of species from these three geographical elements, rare taxa occupy a narrower range of habitats and occur in a lower proportion of suitable stands than do non-rare species. The rare temperate group shows highest species diversity in, and is largely confined to, old Abies—Hylocomium forests. The arctic-montane group exhibits greatest diversity in exposed coastal sites, while diversity of the montane group is highest in freshwater habitats. Relative richness of rare species is high in individual stands of all the habitats occupied by the arctic-montane and montane groups, and varies little among stands. However, relative diversity of rare temperate species tends to be low in individual Abies—Hylocomium forest stands, and both species composition and species richness exhibit considerable among-stand variation. Dispersal potential, as indicated by diaspore type, is negatively associated with rarity, and positively associated with both the number of habitats and proportion of suitable stands occupied. Some possible reasons for the observed patterns of habitat use, and the implications of these results for management and conservation of the rare moss flora of Terra Nova National Park, are examined.