Assessing the vulnerability and conservation potential of old-growth forests in British Columbia, Canada

Climate change is predicted to have widespread effects on the distribution of many species and ecosystems, including old-growth forests. Because of the slow development time of old-growth forests, it is especially important for their management to map and understand areas of “climate change refugia.” British Columbia (BC), Canada, holds globally significant areas of old-growth forests with varying levels of threats from climate change. To better understand these threats, we used Maxent to model climate envelopes of BC's ecosystems, as represented by Biogeoclimatic Ecosystem Classification units. We then projected ecosystem changes for the 2050s climate period and overlaid them with current and potential future old-growth forests (projected to become old growth in the absence of fire) to identify where these forests are likely to persist (“old-growth refugia”) and develop a provincial Refugia Probability Index. Finally, we assessed to what extent BC's current protected areas network represents current and future old-growth forest. Our analysis identified 110,545 km² of old-growth forest in BC as of 2021, which has the potential to increase via natural succession by up to an additional 69,410 km² by 2055, barring future wildfires or other disturbances. We also found that up to 54% of the province and 63% of current old growth fell within the projected area of maximum total refugia for the 2050s climate period. Our results indicate that less than 12% of these forests are currently within protected climate refugia, with under 0.2% in areas of “high” refugia probability. Thus, we demonstrate that almost all old growth in BC is susceptible to climate change, human development, or both, highlighting the vulnerability of these forests into the middle of the century. Overall, over 51% of BC's old growth was identified as susceptible to human development and within the projected area of maximum total refugia. We suggest future planning to focus on conserving elements of these areas, as their projected climate stability potentially translates into long-term protection. We provide a framework for forest and conservation managers to assess the future effects of climate change on old-growth forests in BC or beyond.