Mixed-conifer forest case study

Abstract

Mixed-conifer forests are widely distributed throughout the mountainous regions of California, occurring just below the upper montane elevation belt and typically ranging from 1,000 to 7,000 ft (300 to 2000 m). Common tree species include ponderosa pine (Pinus ponderosa Lawson & C. Lawson) and Jeffrey pine (P. jeffreyi Balf.), white fir (Abies concolor (Gord. & Glend.) Lindl. ex Hildebr.), sugar pine (P. lambertiana Douglas), incense cedar (Calocedrus decurrens (Torr.) Florin), Douglas-fir (Pseudotsuga menziesii (Mirbel) Franco), and black oak (Quercus kelloggii Newberry), and there are numerous, less common hardwood and conifer species, including the rare but iconic giant sequoia (Sequoiadendron giganteum (Lindl.) J. Buchholz). These tree species are differentially adapted to the physical and biotic environment, and forest composition and structure are driven by topographic gradients that influence soil water availability and solar exposure as well as ecological disturbances such as fire, drought, and insect outbreaks (Safford and Stevens 2017). Fire exclusion and logging have been primary drivers in altering composition and structure in mixed-conifer forests. Changes have included loss of fire-tolerant/ shade-intolerant species (e.g., pines, giant sequoia), reduced structural heterogeneity, and increased canopy cover and tree densities (especially in the smallest size classes), leading to elevated woody fuel loads, and reduced habitat quality and diversity (Knapp 2015, Knapp et al. 2013, North et al. 2009, North 2012). Prior to Euro-American colonization, Sierra Nevada mixed-conifer forests experienced frequent (every 11 to 16 years, on average), low- to moderate-severity (mostly surface) fires, but today these fires are relatively rare (Safford and Stevens 2017). In concert with climate change, these changes have catalyzed a trend of larger and more severe fires and bark beetle outbreaks over the past several decades, leading to habitat fragmentation and broad-scale and potentially long-term forest loss (Kolb et al. 2016, Westerling et al. 2006).

Parent Publication

• Postfire restoration framework for national forests in California

Citation

Estes, Becky L.; Meyer, Marc D.; Gross, Shana E.; Walsh, Dana; Isbell, Clint. 2021. Mixed-conifer forest case study. In: Meyer, M.D.; Long, J.W.; Safford, H.D., eds. Postfire restoration framework for national forests in California. Gen. Tech. Rep. PSW-GTR-270. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 71-98. Chapter 4.