Effects of Prescribed Fire on Soil Properties in Oak Woodlands

Oak woodlands are used extensively for cattle grazing, providing approximately 75% of the forage produced on California’s rangelands. Vegetation management is needed in these landscapes to maintain open space, reduce fuel loads, and manage weed infestations. Prescribed fire is an effective vegetation management tool. Recently there has been a great deal of concern regarding the impacts of rangeland management on water quality. We measured the effects of prescribed fire on biogeochemical properties of oak woodland soils.
Prescribed fire treatments were completed in two oak woodland watersheds at UC Hopland and Sierra Foothill research and extension centers. The top 5-cm of soil was sampled before and after burning for nutrient analysis. Biomass was collected before the burn.

Soil organic carbon did not change after prescribed fire. The N returned to soil after fire was low, less than the amount supplied as manure at stocking rates of 3 cows per hectare. Phosphorus has higher volatilization temperatures (>500C) compared to nitrogen (200C), thus the relative amount of P returned to soil after burning high. Results suggest that prescribed fire will not increase nutrient supply to streams since very little N was released. This is likely the case for P because its mobility is limited in soil, however, transport by accelerated erosion may be amplified by fire. (O’Geen, Swarowsky, Lewis Dahlgren, and Tate)

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