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Individual Highlight

Forest soil resilience following biomass thinning and repeated prescribed fire

Photo of Prescribed burning in central Oregon ponderosa pine research plots. Prescribed burning in central Oregon ponderosa pine research plots. Snapshot : The soil organic horizon, or forest floor, it vital to the function and health of most conifer forests. As a source of soil carbon and nutrients, this surface layer also moderates soil temperature and moisture extremes, limits soil erosion, and contributes to wildfire hazard. Forest Service scientists examined 25-year changes in forest floor depth, amount, and ecological function following biomass thinning and prescribed burning in ponderosa pine forests. Their findings revealed a high level of resilience to thinning, and a relatively rapid recovery of the organic layer following burning. More importantly, key ecological functions of the forest floor were not compromised by either fuel-reduction practice during the quarter-century study.

Principal Investigators(s) :
Busse, Matt D. 
Research Location : Deschutes National Forest, central Oregon
Research Station : Pacific Southwest Research Station (PSW)
Year : 2017
Highlight ID : 1338


Forest Service scientists measured long-term forest floor accumulation in young, central Oregon ponderosa pine forests and asked whether selected ecological functions of the surface organic layer were altered by thinning and prescribed burning. Experimental treatments included (1) thin-only in 1989, (2) burn-only in 1991 and 2002, (3) thin and repeated burn, and (4) control site of no thin or burn. Without fire, there was little change in forest floor accumulation for thinned or unthinned stands, indicating balanced litterfall and decay rates in these young forests regardless of tree density. The repeated burns each consumed most of the forest floor, yet post-fire accumulation rates were comparatively rapid, with forest floor depth matching pre-burn levels within 15 to 20 years of treatment. They detected only modest treatment effects on forest floor functions by the end of the study (total carbon and nitrogen pools, litter decay rate, restrictive layer limiting plant emergence, erosion protection, surface fire behavior) despite the temporal differences in forest floor depth and mass. This study highlights a quarter-century of forest floor development and suggests that thinning and burning pose limited risk to the properties and functions of surface organics in these dry, pine forests.

Forest Service Partners

External Partners

  • Deschutes National Forest
  • Oregon State University
  • Region 6 Ecology Program