Date of this Version
Final Report to the Joint Fire Science Program Project #01-3-3-34
A prescribed burn was conducted in a juniper woodland approximately 40 km south of Tooele, Utah on 05 October 2006. Conditions were sub-optimal, and the fire did not encroach into mid- or late-successional areas; only the early-successional area burned successfully. This study evaluated the effects of the prescribed burn on biological soil crusts that occupy the soil surface and are important for soil stability, soil nutrient cycling, and the germination and survival of vascular plants. Biological soil crusts are composed primarily of cyanobacteria, green algae, lichens and mosses. Mosses were rare under juniper trees, so the effects of the fire were negligible; the burn significantly reduced the cover of mosses under sagebrush and in shrub interspaces. Lichens were uncommon under juniper and sagebrush. They were more common in shrub interspaces, but because the fire was spotty and of low intensity in the interspaces, they were minimally affected there. The burn significantly reduced the biomass of green algae and cyanobacteria under juniper and sagebrush; it was unaffected in the shrub interspaces. Similar trends were seen in algal density. This conclusion was confirmed by measurement of the density of green algae and cyanobacteria which also showed a significant decline in juniper and sagebrush understory, but not in the interspaces. Nitrogen fixation was significantly reduced under juniper trees but not under sagebrush or in the interspaces. Nitrogen fixation was approximately an order of magnitude greater in the shrub interspaces than beneath juniper and sagebrush. Because the interspaces were not greatly affected by the burn itself, there was no significant impact on nitrogen fixation there. In general, it appears that, while the burn negatively affected some components of biological soil crusts in some parts of the early successional stage of the juniper woodland, the overall impact on the crusts was minimal. If the intent of prescribed burning is a reduction in juniper, burning of early successional juniper woodland is appropriate because most affected trees were killed. Control of sagebrush can likewise be accomplished by low intensity, cool season fires without eliminating the crust component. Due to the spotty nature of the fire in the shrub interspaces, where most biological soil crusts occur, they were only minimally affected by the fire and may provide a good source of algal inoculants to re-colonize the soil in the juniper and sagebrush vegetation patch types which were more affected by the fire. The data suggest that intense fires should be avoided due to the potential for greater encroachment into the shrub interspaces which contain the majority of biological soil crust organisms. This information, plus the fact that late successional juniper woodlands are difficult to burn, suggests that burning of early successional juniper may be a preferred method for controlling juniper encroachment on western rangelands.
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