Floristic Richness, Area, and Habitat Diversity in a Hemiarctic Archipelago

Vascular plant richness of a hemiarctic archipelago located in Richmond Gulf, northern Quebec, Canada (56010'N, 76'20'W) was studied in relation to island area and habitat diversity. Twenty-two types of habitats were defined using five abiotic variables: substrate, drainage, slope, exposure, and potential snow cover. The flora (271 species) was surveyed separately for each type of habitat on each of the thirty-four islands. For islands as a whole, species richness (S) was highly correlated both with log area (A) (r=0.92) and with numbers of habitats (H) (r=0.98). For individual habitats, S-logA correlations were lower than for whole islands, and varied from r= -0.27 to r=0.93. At the habitat level, the percentages of variance explained by regressions of S on logA were significantly correlated with estimates of species pool sizes. Accordingly, habitats were interpreted as passive samplers of their respective species pools. On the other hand, at the whole island level, S was shown to be controlled by both area and habitat diversity. It is argued that species-area relationships in islands cannot be interpreted unless each habitat is separately considered and analysed.