The Effects of Climatically Altered Fire Regimes on Initial Successional Responses in Yellowstone National Park

Abstract

Many scientists predict that due to the quick response of fire regimes to changes in climate (Flannigan et al. 1998; Stocks et al. 1998), the most rapid and extensive effects of climate change will be mediated by altered disturbance regimes (Davis and Botkin 1985; Franklin et al. 1992; Graham et al. 1990; Weber and Flannigan 1997). Under climate scenarios expected for C02 doubling, Price and Rind (1994) predict a 44% increase in lightning-caused fires and a 78% increase in total area burned for the U.S. Although regional climate scenarios are still subject to a fairly high degree of uncertainty, regional predictions for Yellowstone National Park (YNP) estimate an increase in aridity (Balling et al. 1992) and mean July temperatures (Bartlein et al. 1997), suggesting that fire frequencies could significantly increase in YNP over the next century. While several models have simulated the response of western coniferous forests to altered fire regimes (Baker et al. 1991; Gardner et al. 1996; Keane et al. 1990; Keane et al. 1995; Romme and Turner 1991), little empirical work on the successional responses to different intervals of stand­replacing fire has been incorporated, and remains a critical element in predicting the effects of climatically altered disturbance regimes in forested landscapes. Previous work in Yellowstone has considered the effects of fire severity, fire size and level of serotiny in explaining initial pathways of postfrre succession across the Yellowstone landscape (Turner et al. 1994; Turner et al. 1997). The effects of the third component of the disturbance regime, fire interval, remains largely unexplored, and represents a fundamental link in predicting potential effects of climate change on the Yellowstone landscape. The specific objectives of our research, therefore, were to assess: Are there a significantly different successional responses following different intervals of stand-replacing fire in Yellowstone National Park? Because serotiny exerts a strong influence on initial post-fire succession in Yellowstone (characterized by variation in lodgepole pine densities), we also sought to track stand-level changes in serotiny over time. In order to flesh out a possible mechanism for why postfrre succession may vary depending upon the age at which the stand burns we asked: What is the temporal variation in lodgepole pine serotiny within the park?