Oral Paper

         Conservation Biology

Resilient Restoration: Drought Resilience Amongst Southern California Quercus agrifolia Populations on Tribal Lands

Presenting Author
Alexandra Hoff
Description
The Coast Live Oak (Quercus agrifolia) is a keystone species, providing invaluable ecosystem services and cultural significance. With a large distribution throughout coastal California and northern Baja California, this species provides shelter and food sources for many animals, restores and improves watersheds and mycorrhizal activity through its root system. It is also culturally important to many Tribal communities, providing abundant harvests of acorns to their families. Unfortunately, this species is facing decline due to increased vulnerability to pests, disease, intense drought and high temperatures, exacerbated by climate change and increased urban  development. As such, Q. agrifolia’s resilience in the face of rapidly changing climate is integral to successful conservation and adaptation efforts. We are investigating whether drought tolerance varies amongst and within southern California Q. agrifolia populations, and which are more resilient. To achieve our goals, we collaborated with local tribes, the Climate Science Alliance and UC Riverside as part of the larger conservation project on ‘Resilient Restoration’. We sampled Q. agrifolia acorns from eight populations across southern California, including local tribal lands. Within the Q. agrifolia, exist two varieties: Quercus agrifolia var. agrifolia which has more glabrous leaves and tends to be distributed closer to the coast, and Q. agrifolia var. oxyadenia which has more tomentose leaves and a more southern, inland distribution, potentially serving as an adaptation to prevent water loss. We predicted that trees from within the distribution of Q. agrifolia var. oxyadenia, where there is a hotter, drier climate, will be more resilient to climate change induced stressors such as drought and heat.  To assess the drought tolerance of the eight populations we have conducted a greenhouse experiment and are conducting genomic analysis. In the greenhouse experiment, half of each population were subjected to severe drought conditions, while the rest received a normal watering schedule. Throughout the greenhouse drought experiment, we measured several drought tolerance indicators such as germination, mortality, height, and stomatal conductance. The measurements of these indicators were compared among populations using an ANOVA test. Our results showed statistically significant differences in mortality and height among populations. With some populations having high levels of mortality. The four most southern populations (within the Q. agrifolia var. oxyadenia distribution) did have the lowest mortality rates of the eight sampled. After the drought experiment, resilient trees identified are being rematriated to the Tribal reservations for planting.  In our genomic analysis, we are currently investigating genetic diversity, based on SNP markers, within and between populations, as a potential additional measure of resilience. We expect populations and families with higher heterozygosity to be more resilient to drought. These findings, along with traditional ecological knowledge and cultural practices, will be used to inform conservation efforts on the tribal lands these oaks came from.