Abstract

Bulk Density and Fuel Loads of Ponderosa Pine and White Fir Forest Floors: Impacts of Leaf Morphology.S.L. Stephens, M.A. Finney, and H. Schantz. 2004. Northwest Science 78:93-100

Fire suppression has produced large forest floor fuel loads in many western coniferous forests. Combustion of the forest floor can produce significant ecological effects due to potentially high fuel loads and proximity to living tissues. Duff consumption is estimated from depth changes after burning using species-specific data for bulk density. To quantify forest floor bulk density and fuel loads, 40 white fir and 61 ponderosa pine forest floor samples were randomly collected from Giant Forest, Sequoia National Park. Multivariate ANOVA determined there was a significant difference in both bulk density and fuel load for species and strata. Multiple regression analysis related mean bulk density (Mg ha-1 cm-1) of a given stratum to stratum depth and total depth of the forest floor. Bulk density increased non-linearly with profile depth and varied from 5.35 – 34.97 Mg ha-1 cm-1 (0.053 - 0.35 g cm-3) and 1.84 – 13.92 Mg ha-1 cm-1 (0.018 - 0.139 g cm-3) for white fir and ponderosa pine. Bulk density of the lowest stratum in white fir forest floors is approximately three times greater than ponderosa pine. Forest floor fuel load varied from 6.35 – 146.02 Mg ha-1 and 3.68 – 125.19 Mg ha-1, for white fir and ponderosa pine. Forest floor bulk density and fuel load were non-linearly related to depth for both species but negatively related to total depth for ponderosa pine. Leaf morphology and litter quality of the two species probably affected the bulk density of their forest floors.