Climate-fire-vegetation interactions and the rise of novel landscape patterns in subalpine ecosystems, Colorado

Abstract

O_LIWildfire, when coupled with climate change, may catalyze abrupt shifts in forest vegetation patterns and composition. Such vegetation changes may also feedback to further alter the extent and frequency of fires through changes in forest fuels and their continuity.\nC_LIO_LITo test these expectations, we obtained six fossil pollen records from lakes across a subalpine landscape in Colorado. Forests there may have responded to climate change and widespread wildfires ca. 1000 years ago when a previous study indicates >80% of sites on the landscape burned within a century. The fires coincided with regional warming, but the extent of burning declined before the climate cooled again. Potentially, post-fire changes in fuel structure and composition contributed to a decline in burning while the warmth persisted.\nC_LIO_LIResults of cluster analyses of the pollen percentages indicate that large changes between successive sets of samples coincided with the widespread wildfires at five of the six sites. After the wildfires, sagebrush (Artemisia) and other meadow taxa increased as conifers, especially spruce (Picea), declined across the landscape, indicating that the forests opened.\nC_LIO_LIThe opening of the forests may have created fuel breaks across the mountain range that limited wildfire after temperatures rose [~]0.5 {degrees}C, and the opening became larger as forests opened further during the Little Ice Age (LIA). Pollen assemblages, like those associated with modern bands of meadow and forest at high elevations, known as ribbon forests, only became common across our study sites during the LIA when the effects of the large fires and subsequent cooling interacted.\nC_LIO_LISynthesis. The transition to open landscapes after widespread wildfire is consistent with the hypothesized vegetation-fire-climate feedbacks and illustrates how climate and fire can interact to rapidly transform landscapes, produce novel vegetation patterns, and further interact with subsequent disturbance regimes.\nC_LI