Short‐Interval Fire and Climatic Drying Drive Shrubland‐to‐Herbaceous Conversion Across California

ABSTRACT One of the most profound ecological consequences of rapid global change is abrupt vegetation type conversion (VTC) from one life form to another. Using fractional vegetation cover from 1986 and 2024, we quantified statewide change in non‐forested vegetation across California regions and modeled drivers of shrubland to herbaceous conversion with stepwise logistic regression and gradient‐boosted trees. Across most regions, we found a clear trajectory toward increased herbaceous cover and reduced shrub dominance, and despite different assumptions, both modeling approaches converged on the same hierarchy of predictors. Short‐interval fire was the strongest and most consistent driver of VTC, with additional influence from warm‐season aridity and temperature, proximity to the wildland‐urban interface (WUI), and nitrogen deposition. These results extend decades of plot‐ and landscape‐scale work from southern California to a statewide context, confirming that conversion risk is highest where recurrent fire, climatic drying, and human interface co‐occur, and lowest in cooler, wetter regions with longer fire‐return intervals. Management that avoids short‐interval reburns in shrublands, reduces human ignitions near development, and pairs fuels work with invasive grass control could help to slow or prevent further shrubland loss.