Forest expansion into coastal barrens in Nova Scotia, Canada

Abstract

Coastal barrens are relatively open areas consisting of sparse tree cover and are dominated by shrubby vegetation, primarily from the Ericaceae family. These habitats are generally found within a forest matrix and may represent long lived, stable communities or early successional habitats, eventually giving way to forest expansion. I used aerial photos to quantify the amount of forest encroachment over the last ∼70 years at five major coastal barrens sites and used a GIS to derive topographic and other spatial predictors to classify persistent coastal barrens, persistent forests, and barrens that developed into forests. I also used plot sampling along transects across the forest - barren ecotone in order to assess potential encroachment and changes in forest structure and soil properties within the transition zone between forests and open coastal barrens. Results from the five study sites, representing 3541 points, showed an average of 16% decrease in the area of coastal barrens habitat due to replacement by forest. The best predictors of persistent barrens were elevation and distance to coast, with barrens at relatively high elevations close to the coast. This suggests that climatic and edaphic conditions in areas close to the coast as well as more exposed areas inland may be conducive to the persistence of coastal barren habitat and resist forest encroachment. Results from transects surveyed in 18 forest patches show that forest expansion is occurring from forest patches located within the coastal barren study sites. Three distinct vegetation communities were detected including: forest communities, edge communities, and open coastal barren communities. Soil properties did not significantly differ across the ecotone. Forest patches located within coastal barrens may provide a seed and propagule source from which forest encroachment can occur.