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Better Together: Combined Thinning and Burning Yielded Best Growing Conditions for Ponderosa Pines 20 Years After Treatment

Photo of Hungry Bob fuels treatment site, Wallowa-Whitman National Forest.Hungry Bob fuels treatment site, Wallowa-Whitman National Forest.Snapshot : Dry ponderosa pine forests in northeastern Oregon that received both prescribed fire and mechanical thinning treatments 20 years ago now have the lowest tree mortality and least amount ladder fuels, lowering their risk of severe fire. Study areas treated with only prescribed burns or mechanical thinning also showed improvement over non-treated areas; however, each treatment resulted in different forest conditions. This information can be used by managers to target different forest restoration goals.

Principal Investigators(s) :
McCaskill, George L. , PhD 
Research Station : Pacific Northwest Research Station (PNW)
Year : 2019
Highlight ID : 1585

Summary

Forests in many parts of the western United States are now more prone to large, high-severity fire than they were before aggressive fire-suppression efforts, livestock grazing, and poor harvest prescriptions of the previous century. Forest fuels have accumulated and many dry forests have become more dense, with many more small trees growing per acre in the absence of frequent low-to-moderate severity fire. At the Hungry Bob fuels reduction site, part of a national Fire and Fire Surrogate network of experiments across the U.S. during the 1990s and through 2000s, USDA Forest Service researchers tested the application of mechanical thinning and prescribed burn treatments in the ponderosa pine and Douglas-fir forests of northeastern Oregon. Twenty years later, a researcher with the Forest Service's Pacific Northwest Research Station returned and collected more data. He wanted to determine how the different combinations of fire and thinning affected the diameter growth and crown conditions of the residual ponderosa pine and Douglas-fir trees over the past two decades. The researcher found that a combination of thinning followed by a prescribed burn produced the best diameter growth in ponderosa pines, whereas the thinning only units had the best growth for Douglas-fir. The combination treatment produced trees with the highest crown ratios, meaning ladder fuels were reduced. Based on the 20-year responses, the combination treatments produced the best conditions for stand growth, while limiting fire stress upon residual tree crowns.

Forest Service Partners

External Partners

 
  • Eastern Oregon University