Alvar vegetation in Canada: a multivariate description at two scales

Abstract

Alvars are areas with a distinctive dry grassland vegetation growing in thin soil over level limestone, and they are documented in Scandinavia, the eastern United States, and central Canada. Ordination and classification analysis techniques were used to describe alvar vegetation in Canada at two scales: within one alvar and among four alvar sites. Within one alvar, changes in species composition corresponded to changes in soil depth and biomass. There were two main vegetation types: (i) alvar meadows with complete vegetation cover and (ii) rock flats with incomplete vegetation cover over limestone rock. Among alvars, species composition was related primarily to geographic location. The southern site was distinct from the eastern and northern sites. Relationships between soil depth, plant biomass, and vegetation could also be detected. At within and among alvar scales, tall perennial graminoids dominated sites with deep soil while small annuals and stress-tolerant perennials dominated shallow soil sites. Average biomass levels were strongly positively correlated with soil depth across vegetation types. Average species richness was curvilinearly related to biomass. Our results describe Canadian alvar vegetation and illustrate important differences among alvar sites, showing that a number of these sites need protection to conserve alvar vegetation. Key words: grassland, drought, soil depth, species richness, biomass, conservation.