LB 35-288 - Population decline for plants in the California Floristic Province: Does ecology or geography determine vulnerability?

Mediterranean-type ecosystems like the California Floristic Province are a biodiversity hotspot facing threats from changing climate, land use, and fire regimes in the coming century. Populations may decline because of habitat loss, species-specific ecological limitations, or a combination of these factors. To understand the potential impacts on plant species in this region, we built habitat and population models for six species, incorporating species-specific ecological traits and climate change, land use, and fire regime scenarios. Habitat models were based on species distribution models, while population models were stage-structured with density dependence and dispersal. We combined each species-specific population model with each species-specific habitat model to identify which species were more likely to face population decline because of habitat loss or ecological limitations and where those population declines were likely to occur. Our results showed that under most combinations of habitat and population models, total metapopulation abundance generally followed changes in habitat area over time, leading to substantial population reductions by 2085 under most climate scenarios. Though habitat might recover between 2055 and 2085 for some species under some climate scenarios, population recovery in the population model often lagged behind the habitat model. We also found that the effects of changing fire regimes varied among species, with obligate-seeding ceanothus species showing less decline in fire-prone habitat models but greater decline with less frequent fire, while thick-barked pine species exhibited the opposite pattern. On the subpopulation level, high variance suggests population decline driven by species' ecological traits, while low variance suggests population decline driven by habitat loss. Our study highlights the importance of considering species-specific ecology and habitat loss when predicting the effects of climate change and land use on plant populations. This approach can inform conservation efforts and help estimate future population changes for species with limited data.