| Abstrakt: |
The potential for severe impacts from a wildland fire, with or without a subsequent severe precipitation event, was evaluated in western and central Colorado and in a case-study area, the former Rio Grande National Forest (NF) of the San Juan-Rio Grande NF. The evaluation involved identifying the factors that are conducive to vulnerability and, additionally, the factors that impede or enhance recovery. Forest ecosystem characteristics that can increase vulnerability to the effects of a severe fire, with or without a subsequent severe precipitation event, include: relative flammability of forest floor materials, the location of nutrient storage (above or below ground), depth of soil, site quality, steepness of slopes, propensity to produce hydrophobic soils, and likelihood of mass movement, among others. Ponderosa pine forests appear more vulnerable, with natural regeneration more difficult than for some other types because of the relatively higher flammability of the foliar material in the forest floor, storage of nutrients above ground, and the episodic and infrequent years for good natural regeneration in drier areas. In western and central Colorado, only two subbasins-the subbasin in which Boulder is located and the subbasin south of Denver-had both a high fire-ignition frequency and a high hydrophobicity composite risk index placing them at risk for both fire and erosional overland flow. Construction of a vegetation map showing the forest types most likely to be damaged by a severe wildfire and erosion, particularly on steep slopes, was done using GIS. The forest landscape structure and composition existing today appear as the result of many stochastic factors operating over decades to centuries. Not all of these historic conditions and processes can be duplicated today. Potential losses of organic matter and nutrients from severe fire and subsequent intense precipitation events can be substantial. [ABSTRACT FROM PUBLISHER] |
