Ecological changes on SGang Gwaay over the last millennium: uncovering forest changes and avian activity with respect to human settlement and invasive species

Zvezdin, Alexandra Catalina (2023) Ecological changes on SGang Gwaay over the last millennium: uncovering forest changes and avian activity with respect to human settlement and invasive species. Masters thesis, Memorial University of Newfoundland.

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Abstract

Haida Gwaii (British Columbia) is an archipelago of immense cultural importance to the Haida people and ecological importance for breeding seabirds. In the past millennia, the islands were exposed to multiple stressors (e.g., Indigenous use of the land, European colonisation, invasive species introduction), thus its ecosystems are likely to have changed greatly; however, historical ecosystem trends are unknown and drivers of change difficult to unveil with contemporary field monitoring programs alone. Archeological and anthropological accounts provide short time-scale knowledge about past vegetation and seabird monitoring programs date back to the ~1980s. Thus, understanding long-term cycles of seabird population decline and increase is difficult with these short time-scale and punctual data. This thesis addresses the lack of knowledge regarding ecosystem changes over millennia using a multi-proxy paleoecological approach to reconstruct past ecosystems of SGang Gwaay, Haida Gwaii and uncover vegetation and wildlife changes as they relate to anthropogenic activities at the former Haida settlement of Nintints (UNESCO world heritage site). With a dated sediment core (based on ²¹⁰Pb and ¹⁴C), our results revealed vegetation and seabird changes occurring ov¹er ~1300 years. After the expansion of the Haida population at Ninstints c.a. 1235 CE, terrestrial vegetation declines, particularly with increased harvest of Western red cedar. This decline in vegetation is reflected by a decrease in plant sterols and stanols (sitosterol, stigmastanol), a decrease in lake-water TOC, C/N and δ¹³C values. This decrease in terrestrial vegetation persists for ~800 years following human settlement expansion and is followed by an increase in chlorophyll a, increase in alagal sterols (campesterol, sitosterol/campesterol), increase pond microbial activity (shift in sitosterol/stigmastanol), and changes in diatom assemblages. Dominant diatom taxa post settlement expansion are indicative of increased lake-water turbulence, increased light availability, and a more acidic pH. Rhinoceros auklets (Cerorhinca monocerata) were present on SGang Gwaay throughout the ~1300 year time period as demonstrated by sedDNA PCR, and ornithogenic proxies (trace-metals, δ¹⁵N values). These proxies suggest a population decline after European contact and an additional significant period of decline when Keen’s mice (Peromyscus keeni), a native predator, was consistently detected by PCR. Our results demonstrate that: (1) small-scale tree harvest had broader impacts for geochemical cycles and ecosystem primary productivity that can persist for centuries after initial impact; (2) centennial wildlife population declines might not be captured shorter term population trends inferred through monitoring over decades (e.g., surveys).

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