The effect of fire interval on post-fire understorey communities in Yellowstone National Park.

摘要

In this study, the effect of time interval between subsequent stand-replacing fire events on post-fire understorey cover and composition after the recent event was investigated. The importance of fire interval relative to broad- or local-scale environmental variability in structuring post-fire understorey communities was established. This study was carried out in Subalpine plateaux of Yellowstone National Park (Wyoming, USA) that burned in 1988. In 2000, we sampled understorey cover and Pinus contorta density in pairs of 12-year old stands at 25 locations. In each pair, the previous fire interval was either short (7-100 years) or long (100-395 years). We analysed variation in understorey species richness, total cover, and cover of functional groups both between site pairs (using paired t-tests) and across sites that experienced the short fire intervals (using regression and ordination). We regressed three principal components to assess the relative importance of disturbance and broad or local environmental variability on post-fire understorey cover and richness. Between paired plots, annuals were less abundant and fire-intolerant species (mostly slow-growing shrubs) were more abundant following long intervals between prior fires. However, mean total cover and richness did not vary between paired interval classes. Across a gradient of fire intervals ranging from 7-100 years, total cover, species richness, and the cover of annuals and nitrogen fixing species all declined while the abundance of shrubs and fire-intolerant species increased. The few exotics showed no response to fire interval. Across all sites, broad-scale variability related to elevation influenced total cover and richness more than fire interval. Significant variation in fire intervals had only minor effects on post-fire understorey communities following the 1988 fires in Yellowstone National Park.