The arroyo oak (Quercus brandegeei) is a micro-endemic species in the Cape Region in Baja California Sur, Mexico. Although the species had a wider distribution historically, it is currently confined to the riparian zone of ephemeral streambeds or “arroyos” within the Sierra La Laguna Biosphere Reserve. Due to its narrow distribution and declining populations the species has been assessed as Endangered in the IUCN Red List of Threatened Species. Since 2018, a team of scientists, land managers, and members of the community within the biosphere reserve have been working together to better understand the causes of decline, and develop a science-based, stakeholder-inclusive conservation, recovery and management plan for this important and iconic species. One of the main issues is the lack of seedling recruitment, leading to a population structure dominated by old individuals. To better understand barriers to regeneration we conducted germination and propagation trials with acorns from three different provenances. We also conducted a seedling exclosure experiment to quantify the impact of free-roaming farm animals on seedling survival and growth, as well as to assess the role that microclimate (specifically canopy openness) has on seedling establishment. Results from the >6,000 acorn germination trial revealed a 78.43% average germination rate with 19 average days of latency and 29 days to reach 50% of germination. Although there were differences in acorn morphology and germination across provenance regions, most of the variability was captured at the level of the individual mother tree. The seedling exclosure experiment showed a significant impact of farm animal grazing and trampling for seedlings growing in unprotected areas versus those transplanted to fenced plots. At the 150th day of the study, seedlings under closed canopy had higher mortality rates than those in open cnaopy (P=0.036); however, by the end of the study (1 year after transplant), seedlings growing under open canopy had significantly higher mortality than those grown in the shade, likely because sites protected by canopy had less extreme temperatures (3.64-52.72 ℃) than open canopy sites (0.9-59.93℃). Overall, our research revealed that (1) acorn production and germination for this species are high, (2) livestock grazing and trampling are significant barriers to seedling survival, at least near ranches, and (3) extreme temperatures and drought are an important cause of seedling mortality, mainly during hot summer months. Conserving Q. Brandegeei requires working with multiple stakeholders, including ranchers, to find innovative ways to manage and recover Q. Brandegeei populations.
acorns, germination, drought, livestock