Quantifying Tree Community Assemblages on Habitation sites in the Great Bear Rainforest

Abstract

Identifying how past human actions have influenced their environment is important for understanding how current ecosystems function. Heavy intertidal resource use by Indigenous Peoples for the past several millennia has led to habitation sites containing vast shell midden deposits within their soils, with long-term impacts on soil chemistry and drainage. Here we examine how these shell middens have impacted various forest metrics, such as species diversity, dissimilarity, structure, and seedling recruitment to determine if forest composition on habitation sites differs from the surrounding matrix. Field data was collected within Hakai Lúxvbálís Conservancy on Calvert and Hecate Islands within the Great Bear Rainforest along British Columbia’s Central Coast. Known habitation sites, places with archeological evidence indicating past year-round human occupation, along the coast of Calvert and Hecate Island were used as study sites. Two to three 11.28 m radius plot were randomly placed on habitation sites where adult species were tallied, height (m), and diameter and breast height (DBH) (cm) data was collected. Within the 11.28 m radius plot were five 1 m x 4 m sub-plots, where all seedlings were tallied, and their growing substrate recorded. For adult trees there was no significant between control sites and habitation sites. (p = 0.07). Adult tree communities on habitation sites were significantly dissimilar from the surrounding matrix (p = 0.008). There was no significant difference between seedling diversity on habitation sites and control sites (p > 0.05), and there was no significant difference in dissimilarity between communities (p = 0.1). We found that there were no significant differences between height or DBH for all tree species analyzed. Both western redcedar (Thuja plicata) and western hemlock (Tsuga heterophylla) adult trees were the main drivers of community dissimilarity by having reduced abundance on habitation sites compared to our control sites. Finally, we found that nurse logs, fallen trees that act as a seedbed, were the primary substrate for seedling recruitment with little regeneration on the forest floor (p < 0.001). Our results demonstrate that forest communities on habitation differ only in their measure of stem density, quantified through community dissimilarity, and that no differences in diversity or physiology are seen between control and habitation sites.