Fire history and structure of red fir (Abiesmagnifica) forests, Swain Mountain Experimental Forest, Cascade Range, northeastern California

The fire history and stand structure (size, age, horizontal pattern) of red fir (Abiesmagnifica A. Murr) forests were studied in two 3.0-ha plots and a larger study area (400 ha) on the Swain Mountain Experimental Forest to identify the fire regime and the effects of fire on stand structure. The fire record in stumps spanned the period 1740–1985. Fires occurred in the 400-ha study area on average every 12.9 years (range 1–57 years), in plot 1 every 18.6 years (range 7–47 years), and in plot 2 every 15.7 years (range 1–45 years). Larger fires recorded in both plots and throughout the larger study area occurred every 26.2 years (range 11–47 years). Average fire-free intervals were shorter (7.9 years) during the settlement–pre-fire-sup-pression period (1851–1934) than during the presettlement (1740–1850) (21.4 years) and fire-suppression (1935–1985) (17.3 years) periods. Severe fires initiated large cohorts of red and white fir (Abiesconcolor (Gord. & Glend.) Lindl.), while low-severity fires probably caused thinning and initiated small patches of trees.