Effects of Hillslope Terracing On Soil Properties In Semi-Arid Ponderosa Pine Habitat In Western Montana.

Terracing was done in the Bitterroot National Forest, Montana, from 1965-1974, on slopes that generally exceeded 30% in an effort to increase tree yield.  Terracing, it was thought, would reduce competition for tree seedling establishment, and would also retain more water on the hill-slope. Main timber species planted were Douglas fir (Pseudotsuga mensizzi) and Ponderosa Pine (Pinus ponderosa). Past studies of terraced units measured and assessed tree growth and physiology, but few studies have examined the effects on long term soil productivity. The purpose of this study was to investigate soils from terraced and non-terraced units across the entire Bitterroot National Forest.  We analyzed soil samples for mineral and organic cations, C:N ratio, organic matter, particle size, and pH as they relate to terracing. Tree height and diameter at breast height (DBH) were converted into kg/ha of biomass to compare the differences between the two treatment types.  Preliminary results suggest that tree biomass is slightly higher on terraced plantations, differences in soil C, N, K, Mg, and Ca are minimal, root biomass is higher within terraced (bench & riser combined) units, and changes in bulk density are not apparent. It seems that these terracing activities had no long term detrimental impact on site soil conditions. The information obtained from this study will be used as baseline data to draft and implement future land management and soil conservation plans.