Garry oak ecosystem stand history in Southwest British Columbia, Canada: implications of environmental change and indigenous land use for ecological restoration and population recovery

Abstract

In the Pacific Northwest of North America, endangered Garry oak ecosystems have a complex history that integrates effects of Holocene climate change, Indigenous land management, and colonial settlement during the Anthropocene. In western Canada, Garry oak and Douglas fir recruitment corresponds with the end of the Little Ice Age (LIA; ca. 1870), after the collapse of Indigenous populations but in some cases prior to European settlement. We examined establishment patterns at three sites in southwest British Columbia, each with different edaphic characteristics based on slope, exposure, and drainage. At our Somenos Marsh site on Vancouver Island, we see a clear relationship between Indigenous occupation, subsequent European settlement, and development of an oak woodland, indicating that Indigenous land management was important for development of many Garry oak ecosystems. However, at the Tumbo Cliff site (Tumbo Island, BC), shallow soil xeric conditions, regional climate, and periodic fire were likely drivers of stand and ecosystem development. Finally, at the deep soil Tumbo Marsh site, Garry oak established and grew quickly when conditions were favorable, following the early twentieth century conversion of a saltwater tidal flat into a freshwater marsh. Combining site level historical records, site characteristics, and dendrochronological data provides a greater understanding of the local and regional factors that shape the unique structures of Garry oak ecosystems at each site. This information can be integrated into restoration and fire management strategies for Garry oak ecosystems as well as elucidate the timing of European settler and climate change impacts on these ecosystems.