Influence of topography and forest structure on patterns of mixed severity fire in ponderosa pine forests of the South Dakota Black Hills, USA

摘要

We examined the influence of topography and stand structure on fire effects within the perimeter of the -34 000 ha Jasper fire of 2000 in ponderosa pine (Pinus ponderosa Laws.) forests of the South Dakota Black Hills, USA. We used a remotely sensed and field-verified map of post-fire burn severity (accuracy 69%, kappa statistic 0.54), the Digital Elevation Model, and vegetation databases maintained by the Black Hills National Forest to empirically test relationships at 500 randomly located points ineach of three severity classes. Burn severity was defined as the relative degree of post-fire change based on fire effects on soil, forest floor, and vegetation. This fire burned rapidly, yet created a patchy mosaic of effects (25, 48, and 27% low, moderate, and high severity). Stands burned by low and moderate severity fire had fewer trees (stand density index < 470 with fewer than 230 trees > 13 cm diameter at breast height ha~(-1)) and were found on less steep sites (slope < 18%). Denser stands (stand density index > 470) with larger trees (average stand diameter > 24 cm) or many small trees were more likely to burn with high severity effects. Our results suggest that managers should consider topography and stand structure together when making strategic decisions about which stands to thin or otherwise manage to reduce the severity with which forests will burn in wildfires.