ABSTRACT
On the 2.6-million-acre Boise National Forest (NF) in southwestern Idaho, wildfires have burned nearly 50% of the ponderosa pine forest over the last nine years. Much of this forest has burned with uncharacteristic intensity. The historic fire regime — one marked by nonlethal surface fires that removed dense understories of saplings or pole-sized trees and increased nutrient availability — has changed. The altered fire regime now results in severe, stand-replacing fires that kill large areas of forest and return them to grass- and shrub-dominated landscapes. Preliminary analysis 272 shows the remaining ponderosa pine on the Boise NF could be fragmented, with only isolated patches remaining, within the next 20 years by severe, stand-replacing wildfire.
In partnership with the University of Idaho, the Boise NF has developed a Geographic Information System (GIS)-based “hazard/risk assessment” model that estimates where the forest ecosystems are most at risk to severe, large wildfires burning in conditions outside the historical range of variability (HRV) and evaluates important resources at risk to these fires. The hazard/risk assessment links five submodels. When the submodels are linked, the assessment estimates where severe, large wildfires burning in conditions outside HRV would severely deplete late-successional habitat needed by old-growth-dependent and other wildlife species, accelerate naturally high levels of erosion and sedimentation, and increase the likelihood that identified fish populations will not persist.
The hazard/risk assessment is most appropriately used to approximate the relative size and extent of the fire-based ecosystem problem on the forest— the result of excluding fire from fire-adapted ponderosa pine ecosystems. It is intended to “nest” between the large-scale analysis undertaken as part of the Upper Columbia River Basin assessment and the site-specific evaluation performed for landscape- and project-level analysis.
