Living on the Edge: Spatial Distributions and Edge Relationships of Plant Communities in the Coastal Barrens of the Chebucto Peninsula, Nova Scotia, Canada.

Abstract

Context Coastal barrens support habitat types including wetlands, dwarf shrublands and tree 'islands' as well as rare plant species. Forest expansion, sea-level rise and recreational trails affect plant communities but spatial vegetation patterns within barrens are unknown.Objectives To classify plant communities; to quantify size, shape, spatial distributions, edge relationships and environmental correlates of plant community patches.Methods Landcover maps were created at three 500 m x 500 m coastal barrens sites using high-resolution multispectral aerial imagery. Community patches were compared using size and shape metrics; shared edge length identified adjacent communities. Community distributions were modelled using environmental variables such as elevation and distance to coast.Results Forty distinct plant communities were detected, with shrublands (37.5% total area), dwarf shrublands (23.3%) and bog wetlands (13.9%) being the most abundant. Average patch size was 9.2 m²; average patch density was 951 patches/ha, indicating fine scale community variability. ATV trails occurred primarily in bog wetlands. Dwarf shrublands and some wetland types were closest to the coastline; taller shrublands and tree islands occurred further from the coast. Edge relationships revealed a vegetation height gradient across the forest-barren ecotone: tree islands were mostly adjacent to tall shrub communities, followed by progressively shorter vegetation.Conclusions Topographic variability and distance to coast were important predictors of community distribution. Shrublands and dwarf shrublands dominated the sites; other types including forest and wetland were abundant in certain conditions. Edge relationships among communities allowed identification of those most at risk from trail disturbance, forestation and coastal squeeze.