Forecasting live fuel moisture of Adenostema fasciculatum and its relationship to regional wildfire dynamics across southern California shrublands

In seasonally dry environments, the amount of water held in
living plant tissue—live fuel moisture (LFM)—is central to vegetation
flammability. LFM-driven changes in wildfire size and frequency are
particularly important throughout southern California shrublands, which
typically produce intense, rapidly spreading wildfires. However, the
relationship between spatiotemporal variation in LFM and resulting
long-term regional patterns in wildfire size and frequency within these
shrublands is less understood. In this study, we demonstrated a novel
method for forecasting the LFM of a critical fuel component throughout
southern California chaparral, Adenostema fasciculatum (chamise) using
gridded climate data. We then leveraged these forecasts to evaluate the
historical relationships of LFM to wildfire size and frequency across
chamise-dominant California shrublands. We determined that chamise LFM is
strongly associated with fire extent, size, and frequency throughout
southern California shrublands, and that LFM–wildfire relationships
exhibit different thresholds across three distinct LFM domains.
Additionally, the cumulative burned area and number of fires increased
dramatically when LFM fell below 62%. These results demonstrate that LFM
mediates multiple aspects of regional wildfire dynamics, and can be
predicted with sufficient accuracy to capture these dynamics. Furthermore,
we identified three distinct LFM ‘domains’ that were characterized by
different frequencies of ignition and spread. These domains are broadly
consistent with the management thresholds currently used in identifying
periods of fire danger.