Fire Severity and Intensity During Spring Burning in Natural and Masticated Mixed Shrub Woodlands

Abstract

Fire risk is an ever present management concern in many urban interface regions. To mitigate this risk, land management agencies have expanded their options beyond prescribed fi re to include vegetation mastication and other mechanical fuel treatments. This research project examined fi re severity and intensity in masticated and unmanipulated units that were burned in spring in a Northern California mixed shrub woodland. Mastication treatments signifi cantly altered the fuel profi le, resulting in an approximate 200 percent average increase in woody fuel cover for 1-hr and 1000-hr TLFM size classes, and greater than 300 percent average cover increase in 10-hr and 100-hr TLFM size classes. The mean fl ame length (29 vs. 10 inches/ 74 vs. 25 cm) and fl ame zone depth (20 vs. 6 inches/ 51 vs. 15 cm) were signifi cantly greater (P<0.001) in masticated units than in unmanipulated units as were the mean temperatures at the litter surface (657°F vs. 219°F/ 347°C vs. 104°C) and 1.64 ft (0.5 m) above the litter surface (277°F vs. 59°F/ 136°C vs. 15°C) (P<0.001). Greater fl am- ing and heat release in the masticated units led to increased mortality of overstory and pole-sized oaks and conifers posing confl icts with the management objective of retaining overstory vegetation.