Habitation Sites Influence Tree Community Assemblages in the Great Bear Rainforest, British Columbia, Canada

Kyle Schang,Kieran Cox,Andrew J Trant

doi:10.3389/fevo.2021.791047

Kyle Schang, Kieran Cox + Show 1 more

Open Access

https://doi.org/10.3389/fevo.2021.791047

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Abstract

Identifying how past human actions have influenced their environment is essential for understanding the ecological factors that structure contemporary ecosystems. Intertidal resource use by Indigenous Peoples for thousands of years has led to habitation sites containing vast shell midden deposits and facilitating long-term impacts on soil chemistry and drainage. Here we examine how these shell middens have impacted various forest metrics, such as species diversity, community composition, canopy height, and regeneration recruitment to determine if forests on habitation sites differ from the surrounding matrix. We surveyed known habitation sites with archeological evidence indicating past year-round human occupation, within the Hakai Lúxvbálís Conservancy on Calvert and Hecate Islands within the Great Bear Rainforest along British Columbia’s Central Coast. Our results demonstrate that habitation sites exhibit lower tree species richness, less relative species abundances, as such, displayed lower Shannon diversity and inverse Simpson values. The composition of tree communities on habitation sites was statistically different, with western hemlock and western redcedar densities increasing on non-habitation sites. Conversely, regeneration diversity at habitation sites was more even and exhibited elevated Shannon diversity and inverse Simpson values. The community composition of regeneration was more consistent among habitation and non-habitation sites; however, western redcedar, western hemlock and Sitka spruce were more abundant at habitation sites. For all tree species, maximum height was higher within the habitation sites; however, this trend was the most notable in western redcedar and Sitka spruce, which increased by an average of 4.8 m relative to non-habitation sites. Collectively, our findings suggest that long-term habitation alters forest community compositions. The landscape alterations within habitation sites promote conditions needed to support diverse, even, and abundant regeneration communities and consequently increase the height of the dominant coastal tree species. Thus, our results offer evidence that long-term influence by Indigenous communities have a persistent influence on coastal forests.

Highlights

Human influence on global biodiversity and ecosystem processes have been well-documented, with post-industrial environmental degradation increasing as human populations continue to grow (Steffen et al, 2015; Watson et al, 2016)
Diversity profile plots illustrate that the species richness of adult tree species was lower on habitation sites as only four of the six species were observed
Yellow cedar regeneration was not observed on habitation sites, whereas Pacific yew regeneration was not observed on control sites

Summary

Introduction

Human influence on global biodiversity and ecosystem processes have been well-documented, with post-industrial environmental degradation increasing as human populations continue to grow (Steffen et al, 2015; Watson et al, 2016). The deposition of shell middens by local Indigenous groups for terracing or refuse have had various documented impacts within the Pacific Northwest and can be substantial in size, exceeding 5-m in depth (McLaren et al, 2014) Shell middens in these locations reflect the past activities of occupants, being composed of resources found in the intertidal zone such as bivalve shells, fish bones and other materials such as plant remains, human remains, and rich organic soils. These alternations to forest community composition can persist at the regional and landscape level even after intense resource-use on habitation sites has ceased (Trant et al, 2016; Fisher et al, 2019)

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