In a Ponderosa Pine Forest, Prescribed Fires Reduce the Likelihood of Scorched Earth

The Malheur National Forest is located in the Blue Mountains on Oregon’s eastern side, the portion of the state that lies east of the Cascade Crest. In the mid 1990s, researchers and land managers conceived a suite of experiments to explore the effects of prescribed fire on forest health. The studies were designed to coincide with prescribed burns conducted by the USDA Forest Service. The experiments took place in the Emigrant Creek Ranger District, a remote area dominated by ponderosa pine. One of the research projects aimed to assess soil health after different intervals of fire frequency and in two burn seasons, spring and fall. Overall, the study revealed that return interval and season of burn had few significantly harmful effects on soil health. Fire can, however, affect the soil’s ability to retain moisture, the primary limiting factor in the ability of the tree to thrive.Key Findings

• Water is the number one limiting factor affecting soils and tree health in the eastern Oregon ponderosa pine forest.
• Initial prescribed fire in the fall burned hotter than the second fall burns and the spring burns, but overall effects on the soil were not significantly different.
• Slightly higher tree mortality was observed on the initial fall burn sites, leading to a reduction in canopy cover and warming the forest floor. Warmer soils may affect the hydrology of the soil in subtle ways.
• Overall, few significant differences in soil were observed between spring and fall burns.