Thinning and prescribed fire for ecosystem restoration in rocky mountain forests of British Columbia: changes in physical, chemical and biological properties of forest floors and soil
Switzer, J.M. 2011. M.Sc. Thesis. University of British Columbia
Abstract
Prevention of uncontrolled wildfire and restoration of Rocky Mountain forests can be accomplished through ecosystem restoration practices such as thinning followed by prescribed fire. The objective of this study is to determine how much thinned fuel can be left on the ground without causing fire temperatures high enough to impair soil physical, chemical and biological properties. I assess the effects of different fuel loadings on soil properties (forest floor depth, soil pH, carbon and nutrient levels, and soil bacteria and fungal communities) during the first year after fire and explore relationships among fuel loadings, fire temperatures and indicators of soil health.
Five fuel management treatments were assessed: large piles, small piles, areas of cut-and-leave, deep litter and an unburned control. In all burned treatments, fuel loadings were greatly reduced and maximum temperatures at the forest floor surface ranged from 60 to 850°C. Temperatures were over 300°C for over 3 hours in the large-pile treatment but were lower and of shorter duration in the small-pile and cut-and-leave treatments. The deep-litter treatment had temperatures above 200°C for over 2 hours and complete combustion of the forest floor occurred.
The low moisture content and resulting consumption of the forest floor in the deep-litter treatment resulted in the largest negative impacts on soil chemical and microbiological properties, while few significant differences were evident among the other treatments. Higher nitrate availability and significant increases in pH were found in the forest floors of burned plots and in the mineral soil of the deep-litter treatment. Microbial abundance did not recover to pre-fire levels in any burned treatments after one year, which may be attributed to the persistence of significant increases in pH.
