Causal factors and consequences of mixed-severity fire in Black Hills ponderosa pine forests

The Jasper fire (33,800 ha) of 2000 in the Black Hills, SD, resulted in many patches of low, moderate, and high severity, distributed in roughly equal proportion. There was a significant effect of stand structure and topography on severity despite extreme weather conditions. Relative density, tree size, and slope, ranked in order of importance, were influential in predicting severity. Relative density <40% and slope <18% represent critical thresholds where low and moderate severity were more likely to occur. High stand density presented the most likely scenario for crown or high severity fire.; Tree mortality increased from ∼1 to 16% and 18 to 59% in low and moderate severity patches during the first 3 years post-fire. All trees were killed in high severity patches. Greater reductions in plant cover were seen with greater severity. Herbaceous cover and richness recovered to pre-burned levels in all burned areas within 3 years post-fire. Pre-fire species composition was highly influential in determining post-fire species composition, and we found ∼70% of species regenerated vegetatively. Many small patches of low, moderate, and high burn severity with a high proportion of surviving vegetation likely accelerated rates of recovery.; Two years post-fire, we examined ∼2100 live trees for evidence of dead cambium within low and moderate severity patches. Dead cambium on a significant portion of tree circumference in a tree with live cambium and a vigorous crown was taken as evidence of incipient fire scar formation. Dead cambium was detected on ∼24 and 44% of surviving trees in low and moderate burn severity patches. Tree regeneration densities were low and variable in low and moderate severity patches, and we observed no regeneration in high severity patches. Tree-dominated cover may not return to the interior of large patches where the distance to seed source exceeds ponderosa pine seed dispersal distance for a long time. The pattern of future fire-scarred trees and post-fire cohorts that resulted from the Jasper fire is indicative of a mixed-severity fire regime consistent with fire history reconstructions in Black Hills ponderosa pine forests.