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Estimation of the threshold canopy bulk density to sustain crown fire in lodgepole pine forests.
The propagation of crown fire through a forest canopy has been theoretically modeled. Crown fire models describe fire behavior based on a number of factors including canopy bulk density or the mass of foliage and fine woody fuels per volume of canopy space. We measured canopy bulk density in a stand of lodgepole pine that burned by crown fire in July 2003 to empirically verify crown fire modeling. We indirectly estimated the threshold canopy bulk density needed to sustain crown fire by measuring remaining canopy fuels adjacent to areas burned by crown fire. We established no difference between measurable tree population characteristics in burned and unburned areas. By extension we reasonably assumed that there was no difference in canopy bulk density either. The minimum measured canopy bulk density approaches the threshold canopy bulk density. The threshold canopy bulk density figure is useful to fire and land managers who wish to treat hazardous fuels in urban interface areas by providing a target level of canopy fuels.
Early post-fire plant community successional pathways
Plant community response to fire is dependent on fire severity and environmental gradients such as elevation, soil properties, slope, and aspect. To date few studies have examined long-term trends in plant community composition with such a diverse sampling of plots. Our dataset includes eleven post-fire vegetation plots distributed widely across Yellowstone. The plots were installed between 1977 and 1989 and have been resampled every few years. We collect information on surface fuel loading, ground-layer vegetation, and tree populations. The field phase is on-going; the latest sampling was 2001. Preliminary findings indicate a wide variation in pre-fire forest vegetation composition and abundance. However several years post-burn the plant communities become very similar, dominated by a suite of characteristic post-fire opportunists. Over the next 100-300 years we expect these communities to diverge again, perhaps approaching their pre-fire composition once again.
Monitoring mechanical hazard fuel reduction
Over the last few years much attention has focused on treating hazardous fuels surrounding developed areas to protect structures and ensure firefighter safety in the event of a wildfire. The fire effects crew monitors fuel reduction activities by sampling and providing information on ground and canopy fuel loadings. Hazard fuel reduction seeks a balance between removing hazardous fuels and preserving the esthetics of the landscape. The crew samples overstory tree fuel loading, understory density, and surface fuel loading. Photopoints are used to monitor changes in the scenery. The information is compared to target fuel loads to ensure that management objectives are met.
Assessment of fire severity using satellite imagery
Historically fire severity and extent were mapped on topographic maps by ground crews or from aircraft. Both methods are costly and inefficient, providing simple line drawings with little detail. With the advent of satellite imagery fire perimeters and severity may be mapped at the scale of 30 m (98') pixels. For example, a 1,000 ha (2,500 acre) fire is composed of over 14,000 individual picture elements in the satellite image, each representing some level of fire severity and providing an unprecedented level of information. In order for the satellite image to be meaningful the information that the satellite "sees" must be correlated with observed conditions on the ground. The correlation is called ground-truthing. The fire effects crew walks each eligible burn assessing fire severity information which is used to ground-truth the image. When complete the images will be used to update the vegetation and fire history layers of the park's geographic information database and become usable to resource managers and researchers. See these links for more information: Normalized Burn Ratio and Composite Burn Index.
A fire history database for Yellowstone National Park 1931-2004.
Yellowstone National park has sporadic records of fires dating back to the 1880s. After 1930 records were consistently kept but differences in filing and storage over the years prevented their general use. Beginning in 2000 the Fire Management Office researched and collected all the information from the archives and created a systematic database consisting of narrative and spatial data. Fire perimeters were created in the park's geographic information database for fires >40 ha (100 acres). Smaller fires were mapped as points. All related information for each fire was transcribed into a searchable database.
FMH protocols in Yellowstone
Yellowstone's fire effects monitoring crew became established in 1998. Installation and monitoring of standard fire effects monitoring plots occurred in 1999. To date approximately 25 plots have been established in hazard fuel reduction areas and proposed prescribed burn units, but mostly installed ahead of naturally ignited fires. Of the latter set of plots about one half are burned by the fire, providing pre- and post-burn data. The majority of initial monitoring efforts were directed at the park's extensive lodgepole pine forests. However we are now focusing attention on the less represented Douglas-fir forests in the northern, lower elevation areas of the park, and whitebark pine forests at high elevation. These plots are used to relate fire behavior to vegetation and fuel loading, and to track long-term changes in the ecosystem as a result of fire.
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