Postglacial fire and vegetation histories of a mid-elevation mixed-conifer forest in the Gallatin Range, MT, USA

Abstract

A 13,500-year-old record from Langohr Wetland in the Gallatin Range of southwestern Montana offers new insights into the vegetation and fire history at middle elevations within the Greater Yellowstone Ecosystem. Pollen data suggest that following deglaciation, a tundra–steppe established until warmer and wetter conditions than before could support Picea parkland. The development of an open, predominantly Pinus mixed-conifer forest from ca. 9300–7000 cal yr BP suggests warming summer temperatures led to an increase in forest cover and fire activity; the increase in tree abundance supported infrequent, stand-replacing fires approximately every 600 years. Picea and Pseudotsuga increased their presence at ca. 7000 cal yr BP, and the mixed-conifer forest became denser during the Mid- and Late Holocene, suggesting summers became cooler and wetter. The additional fuel load led to increased fire activity, with stand-replacing fires occurring approximately every 350 years in the Late Holocene. The forest surrounding Langohr Wetland experienced less change in vegetation composition and structure and fewer fire episodes than other low- and high-elevation sites in the Greater Yellowstone Ecosystem. The stability of this forested ecosystem over thousands of years is likely a result of its cool mesic mid-elevation setting, limiting the frequency of intense fire episodes.