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Central Oregon fire history: fire and forest histories of central Oregon from tree rings

Status: 
Action
Dates: 
January, 2009 to December, 2015

Central Oregon currently lacks the site-specific fire and forest histories that are necessary for scientifically based land-management planning in the region. For a region with such extensive fire-adapted ecosystems, surprisingly few fire and forest histories have been reconstructed from tree rings, and these only at stand scales and in only a few of the region's forest types.

Approach

For a region with such extensive fire-adapted ecosystems, surprisingly few fire and forest histories have been reconstructed from tree rings, and these only at stand scales and in only a few of the region's forest types. In addition, climate change is recognized by the chief of the Forest Service as one of three critical new resource issues for the 21st century (http://www.fs.fed.us/climatechange).

Anticipating the effects of climate change on future fire requires that we understand the effects of climate variation on past fires. It also requires that we bridge the past, present, and future by identifying the climate drivers of 20th-century fires from written archival records, and using this information to project future fire regimes. Finally, there is an urgent need to collect tree-ring evidence of past fires because modern prescribed burning and extensive, severe wildfires are rapidly and permanently consuming this evidence.

In cooperation with the Central Oregon Fire Management Service (Deschutes and Ochoco National Forests and the Prineville District of the Bureau of Land Management) and The Nature Conservancy, we began reconstructing fire and forest histories from tree rings in central Oregon in the summer of 2009. .

Goals and Objectives

  1. Reconstruct annually accurate multi-century fire and forest histories from tree rings sampled systematically at seven sites (approximately 1200 ac (500 ha)/each). Of these, five sites will span a range of forest types but be centered on mixed-conifer forests (two sites on the east-slope of the Cascades and three sites in the Ochocos). One site will be dominated by western juniper and one site by lodgepole pine.
  2. Identify the climate drivers of past regional-fire years in central Oregon from our tree-ring data, and for modern regional-fire years from written archival records of fire. Use these calibrations to project future fire regimes using regional climate scenarios.

Key Findings

For centuries (1650–1900), extensive mixed-severity fires occurred every 26 to 82 years, creating a multi-aged forest and shrub mosaic. Simulation modeling suggests that the historical mix of surface and passive crown fire were primarily driven by shrub biomass and wind speed. However, a century of fire exclusion has reduced the potential for the high-severity patches of fire that were common historically, likely by reducing bitterbrush cover, the primary ladder fuel. This reduced shrub cover is likely to persist until fire or insects create new canopy gaps. Crown fire potential may increase even with current fuel loadings if the climate predicted for midcentury lowers fuel moistures, but only under rare extreme winds. This study expands our emerging understanding of complexity in the disturbance dynamics of lodgepole pine across its broad North American range.

Publications

Other

For additional information, please visit https://www.firelab.org/project/central-oregon-fire-history



Project Contact: 

Principal Investigators:
Rachel A. Loehman - USGS
Donald A. Falk - University of Arizona