Implications of spatially extensive historical data from surveys for restoring dry forests of Oregon's eastern Cascades

Abstract

Abstract. Dry western forests (e.g., ponderosa pine and mixed conifer) were thought to have been historically old and park-like, maintained by low-severity fires, and to have become denser and more prone to high-severity fire. In the Pacific Northwest, early aerial photos (primarily in Washington), showed that dry forests instead had variable-severity fires and forest structure, but more detail is needed. Here I used pre-1900 General Land Office Surveys, with new methods that allow accurate reconstruction of detailed forest structure, to test eight hypotheses about historical structure and fire across about 400,000 ha of dry forests in Oregon's eastern Cascades. The reconstructions show that only about 13.5% of these forests had low tree density. Forests instead were generally dense (mean ¼ 249 trees/ha), but density varied by a factor of 2-4 across about 25,000-ha areas. Shade-tolerant firs historically were 17% of trees, dominated about 12% of forest area, and were common in forest understories. Understory trees and shrubs dominated on 83.5%, and were dense across 44.8% of forest area. Small trees (10-40 cm dbh) were .50% of trees across 72.3% of forest area. Low-severity fire dominated on only 23.5%, mixed-severity fire on 50.2%, and high-severity fire on 26.2% of forest area. Historical fire included modest-rotation (29-78 years) lowseverity and long-rotation (435 years) high-severity fire. Given historical variability in fire and forest structure, an ecological approach to restoration would restore fuels and manage for variable-severity fires, rather than reduce fuels to lower fire risk. Modest reduction in white fir/grand fir and an increase in large snags, down wood, and large trees would enhance recovery from past extensive logging and increase resiliency to future global change. These forests can be maintained by wildland fire use, coupled, near infrastructure, with prescribed fires that mimic historical low-severity fires.

Historical and current landscape‐scale ponderosa pine and mixed conifer forest structure in the Southern Sierra Nevada

“…Baker (2012Baker ( , 2014 used this system (GLO), which used eight trees per section (259 ha) that were marked to assist in the relocation of survey section corners, to reconstruct historical forest conditions in eastern Oregon and the Sierra Nevada. Four townships (or 144 sections) in eastern Oregon (Baker 2012) overlap an area that used similar historical transect data analyzed in this work (Hagmann et al 2013).…”

“…Baker (2012Baker ( , 2014 used this system (GLO), which used eight trees per section (259 ha) that were marked to assist in the relocation of survey section corners, to reconstruct historical forest conditions in eastern Oregon and the Sierra Nevada. Four townships (or 144 sections) in eastern Oregon (Baker 2012) overlap an area that used similar historical transect data analyzed in this work (Hagmann et al 2013). GLO survey data collected in 1866-1895 would include a record of approximately 1152 trees marking section and quarter section corners in this four township area while the historical timber transect inventory included 163,558 trees on 1355 transects (Hagmann et al 2013).…”

Effects of Fire and Commercial Thinning on Future Habitat of the Northern Spotted Owl

“…In contrast, previous published assessments of fire on spotted owls have not explicitly considered fire and forest regrowth rates (Wilson and Baker 1998, Lee and Irwin 2005, Roloff et al 2005, 2012, Ager et al 2007, Lehmkuhl et al 2007. Not including the probability of high-severity fire, which is low, leads to highly inflated projections of the effects of thinning versus not thinning on high-severity fire (Rhodes andBaker 2008, Campbell et al 2012).…”

“…In addition, it is becoming increasingly less clear whether a reduction in high-severity fire below current rates would necessarily be beneficial to spotted owls. The dry forests in which spotted owls are found were historically characterized by mixed-severity fires (see Hessburg et al (2007), Baker (2012), and Odion et al (2014) for historic fire in the dry Cascades of Washington and Oregon, Beaty and Taylor (2001) and Taylor (2001, 2010) for the California Cascades, and Wills and Stuart (1994), Skinner (1998, 2003), and Odion et al (2014) for the Klamath). Recent research suggests that this historic fire may have neutral and beneficial effects to spotted owls.…”

“…Previous assessments of the efficacy of thinning treatments in reducing fire disturbances in spotted owl habitat (Wilson and Baker 1998, Lee and Irwin 2005, Roloff et al 2005, 2012, Ager et al 2007, Lehmkuhl et al 2007 have not incorporated the probability of high-severity fires occurring during the treatment lifespan. The effect of this is to overestimate treatment efficacy in potentially controlling fire or fire behavior (Rhodes and Baker 2008).…”