Distribution of Fine Roots of Ponderosa Pine and Douglas-Fir in a Central Idaho Forest

This study describes soil horizon depth and fine root distribution in cores collected at two distances from the boles of Douglas-fir and ponderosa pine trees at a study site in a central Idaho forest. Concentration and content of fine roots extracted from soil cores were compared among species, soil horizons, tree size, and distance from bole. Approximately 80% of litter and humus samples contained no fine roots. The highest fine root content and concentrations of fine roots occurred in deep mineral soil for both species (1.24 g and 2.82 g/l for Douglas-fir and 0.98g and 2.24 g/l for ponderosa pine, respectively). No statistically significant differences were found in fine root content or concentration between species in any of the four soil horizons. Tree size was not a significant factor in fine root distribution in this study. Significant variables were horizon, distance from bole, and interactions among tree size, location of sample, and soil horizon. This study, which was part of a larger US Forest Service study to develop a predictive model of postfire tree mortality, provides baseline information that may be useful in predicting postfire damage to fine roots.