Vegetation patterns across edges of bogs and lakes in spruce and hemlock forests of southwestern Nova Scotia

Abstract

Although forest edges surrounding lakes and wetlands are common in many heterogeneous landscapes, there are few studies on patterns of vegetation across these natural landscape boundaries. We investigated forest structure, understorey composition and bryophytes at bog and lakeshore edges in spruce and old-growth hemlock forests. Our objectives were to estimate edge width for vegetation across lake and bog edges, and to examine patterns across the bog-forest edge. We sampled canopy cover, trees, deadwood, structural diversity, species diversity, saplings, and understorey vegetation along transects across four bog and four lakeshore edges in spruce forests and five lakeshore edges in hemlock forests. We used randomization tests to determine the distance of edge and forest influence into adjacent interior forest and bog, respectively. Patterns were assessed using wavelet analysis to determine locations of abrupt changes. Edge influence extended only 5 m into the forest for most variables with notable results of fewer bryophytes, more shrubs and greater tree and shrub diversity at lakeshore edges in hemlock forests. Forest influence at bog edges resulted in a wider approx. 40 m transition zone within the bog in which tree density, graminoid cover, Sphagnum spp. cover, and herb diversity were greater than both adjacent bog and forest. Varying edge width and responses to edge influence between forest types emphasizes the need for site-specific studies. Lakeshore and bog-forest edges harbor greater diversity and unique vegetation structure on heterogeneous landscapes in Nova Scotia, particularly in bog margins, and are key areas to consider for conservation.