| An emerging technology, airborne laser altimetry, is applied to the problem of remotely sensing surface fuel characteristics beneath closed-canopies of lodgepole pine (Pinus contorta Dougl. ex Loud.) in west-central Montana, U.S.A. Its ability to provide effective discrimination of FPBS (fire behavior prediction system) fuel models and accurate estimates of coarse woody debris is successfully validated using plot data with coincident field and laser altimetry-based estimates of fuel bed parameters. The surface roughness metrics of obstacle density, standard deviation of the ground-height distribution (GHD), and kurtosis of the GHD correlate highly with field estimates of fuel volume/load/surface area. These relationships can be exploited to predict fuel attributes at the plot-level (r2 ∼ 0.8). The observed relationships are driven by coarse woody debris in the fuel bed, and not by live biomass or smaller dead fuels. Further, it appears that surface roughness does not depict discreet fuel entities, but rather that woody debris causes scattering of incident laser radiation such that the apparent ground surface of heavily loaded plots is highly variable relative to those with less fuel accumulation. Comparison of a laser-derived continuous 1000-hr fuel surface (>3-inch diameter pieces) with both plot-level and area-based field estimates demonstrates that plot-level relationships are scalable to the landscape, and that laser altimetry is useful for characterizing both the distribution of fuel accumulations and their within- and between-patch variability. However, it appears unable to assist in discrimination of rough surfaces caused by the presence of coarse woody debris and those caused by geomorphic roughness. The 1000-hr fuel surface is spatially consistent with independently-derived photomorphic units from high spatial resolution optical imagery and with fire history. Specifically, regions characterized by heavy fuel accumulations correspond with texturally rough canopies and the occurrence of single fires that burned at least 250 years ago. In regions with lighter fuel loads and more complex fire histories, these relationships break down, lending credibility to the idea that laser altimetry-derived fuel maps may be helpful for documenting fire history in mixed-severity regimes characterized by episodes of frequent fire activity. (Abstract shortened by UMI.)... |
