Substitute oaks: Modeling human-assisted dispersal of climate-threatened foundation species

Climate change is causing the global decline of important foundation species, threatening the loss of ecological function. Human-assisted dispersal can mitigate this loss by relocating species to climatically suitable areas beyond their historical ranges. Moving beyond a method of range expansion for climate-threatened species, we adapted this into a substitution-based approach: replacing lost populations with nearby, functionally similar congeners. We tested this framework by modeling the future distributions of seven culturally and functionally important endemic oak ( Quercus ) species across the California Floristic Province and identifying which areas were projected to lose species but could be substituted with another. We found that around 60% of current oak habitat may lose species by the end of the century, with over 30% losing all oaks. Substitution-based assisted dispersal could mitigate this decline, potentially replacing around 10% of current habitat. However, species projected to decline most under climate change were the least viable donors, while oak species projected to remain relatively stable were common donor candidates. We frame substitution-based assisted dispersal as a proactive approach that directs ecosystems toward functionally analogous states while minimizing ecological novelty.