U.S. Joint Fire Science Program


Joint Fire Science Program Synthesis Reports

Date of this Version


Document Type



Forest Guild, US Forest Service, May 2011


US government work.


The goal of this guide is to provide a resource for managers of mixed conifer forests of the Southwestern plateaus and uplands, the Central and Southern Rocky Mountains, the Sierra Nevada, and the Transverse and Peninsular Ranges in Southern California. Mixed conifer forests have different species, structures, and spatial patterns in these regions but, in general, we focus on forests with a mix of ponderosa or Jeffrey pine, Douglas-fir, true firs, and aspen. The guide includes a comprehensive review of historic conditions, past land use, natural fire regimes, impacts of altered fire regimes, and future prospects, given climate change, for mixed conifer forests. The second half of the guide addresses fuels treatment objectives, techniques, barriers, and successes across a range of ownerships. Before Euro-American settlement of the West, fires in mixed conifer forests burned on intervals that averaged between eight and 25 years for the Sierra Nevada, Southern Rockies, and Southwestern mixed conifer. Low-severity fires were more frequent in some mixed conifer forests; but, in general, mixed conifer forests have historically tended to be heterogeneous mixtures in which species composition, forest structure, and fuel loads change over short distances. Since Euro-American settlement, many mixed conifer forests have become more homogeneous and can therefore facilitate larger, higher-severity fires than those that occurred historically. Increasing heterogeneity in mixed conifer forests at the landscape scale to approximate historic conditions is important for achieving many management objectives, from fuel reduction to wildlife habitat. Restoration and wildfire hazard reduction are not synonymous, but restoration treatments can reduce the risk of uncharacteristic high-severity fire, i.e., standreplacing fire covering a large portion of the landscape. This report discusses prescribed fire, silvicultural treatments, and combinations of cutting and burning. In most mixed conifer forests, thinning that treats both the canopy and understory (crown and low thinnings) combined with prescribed fire is the most effective way to reduce wildfire hazard. However, land management objectives or external constraints can make other tools, such as mastication or prescribed fire alone, more appropriate. Treatments must be maintained for their fuel reduction effect to be sustained, and no single treatment will reverse a long history of fire exclusion. After about ten years, fuels begin building up towards pretreatment levels in many mixed conifer forests. Interviews with 75 managers and experts helped identify numerous complications and barriers to implementing fuels treatments in mixed conifer forests. Smoke management and wildlife habitat protections are two common issues that can make these treatments more complicated, though not impossible. This report also discusses institutional challenges, such as the loss of local expertise and experience with fire that occurs with retirement. Another institutional challenge to returning natural mixed-severity fire regimes that include patches of high-severity fire to mixed conifer landscapes is the need to build confidence within an organization. Organizations and the public can be wary of prescriptions that include patches of high-severity fire, but landscape-level treatments that reduce wildfire hazard and increase the ability to control fires help build confidence that prescribed mixed-severity fires can be implemented safely. Another consistent challenge to implementing fuels treatment is funding. Organizations that enjoy community support and strong partnerships through collaboration have allies in the battle for scarce resources and a strong case for grant funding. Though collaboration requires an investment of time and money, it can help avoid even more costly litigation or obstruction. Collaboration helps managers identify objectives that meet broad stakeholder social, economic, and ecological goals. While research questions and management challenges remain, this report documents both the extensive scientific knowledge and the practical management insights that already exist about fuels treatment in mixed conifer forests.