Spatial heterogeneity of lodgepole pine sapling densities following the 1988 fires in Yellowstone National Park, Wyoming, USA

Abstract

Large disturbances create spatial heterogeneity in vegetation re-establishment, and documenting such variability is critical for understanding and predicting succession. We quantified the spatial heterogeneity of lodgepole pine sapling densities 10 years after the 1988 fires in Yellowstone National Park using color infrared orthophotographs. Densities were classified across the landscape at an accuracy of 70.9%, and landscape metrics were used to characterize their spatial variability. Densities ranged from 0 to > 500 000 saplings/ha, but >60% of the burned area was represented by densities <5000 stems/ha. The burned area consisted of small patches averaging 1.5 ha in area at a mean patch density of 68 patches/100 ha. Densities occurred in nearly equal proportions across the landscape (Shannon's evenness = 0.85) but were well dispersed (contagion index ≈ 20%), suggesting that densities varied in a complex, fine-grained mosaic across the landscape, with high-density patches occurring within a matrix of larger, lower density patches. High-density patches were similar in area to severe surface fires, suggesting that burn severity is an important explanatory variable for spatial variation in sapling density. Large, stand-replacing fires may result in heterogeneous forest landscapes rather than homogenous forests of uniform structure, which may have important consequences for postfire ecological processes.