Bedrock meadows: A distinct vegetation type in northwestern North America

Abstract

Aims:In northwestern North America, montane meadows fed by vernal ground-flow seepage occur scattered throughout an otherwise forested landscape on shallow soils over bedrock. Although their significance for biodiversity has been known, they have never been subject to systematic scientific research and thus, are not included in regional or national vegetation classification schemes. We provide the first vegetation survey of bedrock meadows and compare them to other major non-forest vegetation types in the region.Study area: Northwestern North America (United States, Canada). Methods:We surveyed 110 plots of bedrock meadow vegetation in Montana, Idaho, and British Columbia and compared them with data from 1052 plots from six studies of other open vegetation in the region: prairie and foothill grasslands, maritime mountain, alpine, and timberline meadows. We used cluster analysis to identify groups based on vascular plant composition, related abiotic and structural characteristics to clusters using non-metric multidimensional scaling (NMDS), and compared proportions of plant growth forms and life spans.Results: Cluster analysis identified five groups, with bedrock meadows forming a distinct community. According to the NMDS, bedrock meadows had a high cover of vascular plants, bryophytes, and lichens and a low cover of litter. Their climate was intermediate between maritime mountain and interior timberline meadows. A distinct functional feature of bedrock meadows was their high proportions of annual plants (therophytes) and plants regenerating from bulbs and corms (geophytes)-a functional composition they shared with maritime mountain meadows. Conclusion:Bedrock meadows have distinct floristic, functional, and environmental features, are important hotspots for biodiversity, and host several rare plant species.They are an important habitat for conservation and environmental impact assessment and should be incorporated into regional and national classification schemes. Future research priority should be given to understanding their spatial extent, ecological functioning, and drivers of non-vascular and vascular species richness.