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    Author(s): Kelly Larvie; Tadashi Moody; Jodi Axelson; Christopher Fettig; Peter Cafferata
    Date: 2019
    Source: California Forestry Note
    Publication Series: Miscellaneous
    Station: Pacific Southwest Research Station
    PDF: View PDF  (972.0 KB)

    Description

    This paper summarizes the 2012-2017 bark beetle epidemic in the Sierra Nevada and its implications for long-term changes in tree species composition and forest structure. Preliminary plot and landscape-scale data are reviewed, showing higher levels of mortality for pine species and greater impacts in the southern Sierra Nevada compared to the northern portions of the range. The federal government owns approximately three quarters of the forested area impacted by high levels of tree morality, with the remainder of the land controlled by nonindustrial (18%) and industrial (6%) ownerships. The accumulation of dead and downed fuel and standing dead trees is expected to increase fire intensity and severity, and pose significant hazards for fire control efforts.

    Potential long-term changes in Sierra Nevada forest composition were explored with a GIS analysis conducted for the Sierra National Forest, located in the southern Sierra. GIS layers included very high fire threat, aspect, high tree mortality, topographic position classification, and climatic exposure. A factor of one was assigned to each parameter (i.e., no weighting for any of the variables). The modeling showed that 4% of the Sierra National Forest is at very high risk for type conversion from mixed conifer to shrublands, and 12% is at high risk. This information can inform landowners regarding the general locations where successful reforestation will be most challenging, as well as illustrate the scale of concern for one national forest in the southern Sierra Nevada.

    Changes to disturbance regimes, continuing land use changes, and climate change with associated species shifts pose significant challenges for maintaining healthy and resilient forests in the Sierra Nevada. Significant unknowns exist regarding the future species composition for vast portions of this region, but type conversions from mixed conifer to shrublands or oak/grass/woodland appear likely for some areas. Recommended best management practices focus on reducing tree densities, achieving successful reforestation, and using adaptive management in the face of currently unknown future changes in growing conditions. With the exception of the bark beetle epidemic in southern California in the early 2000s, lessons learned from other locations in western North America that have had sustained bark beetle epidemics in the past decade are not directly applicable to Sierra Nevada, with its Mediterranean climate, complex topography, and mixed-conifer forests. For these reasons, ongoing research efforts to characterize and understand tree mortality drivers and changes in forest structure and composition in the Sierra Nevada are extremely important.

    Publication Notes

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    • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.

    Citation

    Larvie, Kelly; Moody, Tadashi; Axelson, Jodi; Fettig, Christopher; Cafferata, Peter. 2019. Synthesis of research into the long-term outlook for Sierra Nevada forests following the current bark beetle epidemic. California Forestry Note. Sacramento, CA: California Natural Resources Agency, California Department of Forestry & Fire Protection. 30 p.

    Keywords

    drought, climate change, tree mortality, western pine beetle

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https://www.fs.usda.gov/treesearch/pubs/58894