The official blog of the Joint Fire Science Program

The official blog of, the Interagency Joint Fire Science Program.

February 10, 2012

Synthesizing Knowledge and Science for Mixed Conifer Forests

A Guest Post by Dr. Zander Evans

JFSP recently released the latest in its series of fuel treatment syntheses that covers the mixed conifer forests of California, Central and Southern Rockies, and the Southwest. The southern mixed conifer fuel treatment syntheses uses nearly 380 scientific articles, agency reports, and other references to answer questions about historic conditions, fire regimes, the impact of altered fire regimes, fuels treatment effectiveness, and treatment impacts. A central goal for the guide is to combine existing peer-reviewed literature and information gathered from dozens of interviews with managers.

The synthesis highlights the importance of heterogeneity in mixed conifer forests. Pre-settlement 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 the late 1800s, logging, fire suppression, road building, and livestock grazing have reduced the frequency of fire and increased tree densities-resulting in more homogeneous forests.

Currently, many fuel treatments seek to restore heterogeneity, i.e., the mosaic of openings and stands of varying densities across the landscape. Rather than just removing trees to create evenly spaced crowns, managers are experimenting with creating gaps and openings to change fire behavior. Innovative managers are creating more landscape heterogeneity by implementing prescribed burns across large mixed conifer forests, such as early season prescriptions using aerial ignition to burn upslope where remaining snow can control the fire. Of course fuel treatments are also designed to reduced wildfire hazard and 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 do that. 

Stephens Lab | University of California Berkeley
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. The synthesis also discusses numerous complications and barriers to implementing fuels treatments in mixed conifer forests such as smoke management, wildlife habitat protections and retirement of experts, that can make these treatments more complicated, though not impossible.

We hope you find this guide useful, and look forward to your feedback.

Zander Evans is Research Director for He can be reached at, by phone at 505-983-8992, ext.36, and via Twitter @forestguild

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