Hydroclimate-driven ecological and fire regime shifts in a unique forest biome of Baja California since the mid-Holocene

Baja California, Mexico occupies a climatically sensitive peninsular setting between the cool Pacific Ocean and the comparatively warmer Gulf of California. This Mexican state is home to a large spectrum of environmental conditions and diverse ecology, due in part to the compounding effects of variable precipitation from El Niño Southern Oscillation (ENSO) cycling and the North American Monsoon (NAM) across a topographical gradient. Near the center of the state resides Sierra de San Pedro Mártir, a high elevation mountain range at the tip of the California Floristic Region, forming a California Mountains ecoregion that is drastically different in biodiversity than the area that surrounds it. Sierra de San Pedro Mártir is a pine-dominated forest that receives ~75% of its annual precipitation during winter months, making it particularly sensitive to ENSO-driven hydroclimatic variability. Notably, this forest has only recently seen the emergence of fire management strategies.

In a palaeoecological reconstruction from this region, a high-resolution fossil pollen record, coupled with macro-charcoal analysis, highlights shifting dominance between precipitation sources through the middle to late Holocene. More contemporarily, however, the impacts of fire suppression can already be seen in the palynological record. Methods of inferential statistics are employed alongside a traditional time series, and cohesion between these two methods of data analysis provides additional confidence in a compelling and robust precipitation-fire-ecology relationship detected through generalized linear regression. This finding has significant implications for the future of fire management in this unique environment, representing the integrative potential for high-resolution palaeoecological research. As this environment represents a natural laboratory for studying ENSO and NAM, this finding additionally has implications for how these two hydrological systems contribute to the future of more regional conservation and restoration.