California Agriculture

Anecdotal and fire behavior modeling evidence indicates that livestock grazing can reduce herbaceous fuels and improve ecosystem resilience in an era of expanding and intensifying wildfires. To quantify these effects in California, we established a statewide, multi-year (2020 to 2022) study manipulating herbaceous biomass levels within prescribed fire footprints to examine the relationship between herbaceous biomass levels and key fire behavior metrics. We identified multiple biomass thresholds that may be incorporated into land management and planning documents. Grasslands with fewer than 384 pounds (lb) per acre (43 grams per square meter [g/m²]) biomass had greater than 90% probability of stopping a fire before reaching 33 feet (ft) (10 meters [m]) while grasslands with biomass greater than 1,248 lb/acre (140 g/m²) had a near zero probability of stopping a fire before reaching 33 ft. Biomass values below 2,496 lb/acre (280 g/m²) had only a 3% probability of reaching 4 ft (1.2 m) flame height. These biomass thresholds and associated fire behavior metrics can be strategically employed to manage grasslands to protect California’s communities in the context of meeting other goals, including minimum residual dry matter standards.