Regionalization of fire regimes in the Central Rocky Mountains, USA

a r t i c l e i n f o Fire is one of the most important natural disturbances in the coniferous forests of the US Rocky Mountains. The Rocky Mountains are separated by a climatic boundary between 40° and 45° N, which we refer to as the central Rocky Mountains (CRM). To determine whether the fire regime from the CRM was more similar to the northern Rocky Mountains (NRM) or southern Rocky Mountains (SRM) during the Holocene, a 12,539-yr-old sediment core from Long Lake, Wyoming, located in the CRM was analyzed for charcoal and pollen. These data were then compared to charcoal records from the CRM, NRM and SRM. During the Younger Dryas chronozone, the fire regime was characterized as frequent at Long Lake. The early and middle Holocene fire regime was characterized as infrequent. A brief interval from 4000 to 3000 cal yr BP, termed the Populus period, had a frequent fire regime and remained frequent through the late Holocene at Long Lake. In comparison to sites from the NRM and SRM, the fire regime at Long Lake was most similar to the SRM during the past 12,539 cal yr BP. These results suggest the disturbance regime in the CRM has a greater affinity with those of the SRM. Introduction Driven by factors such as temperature, precipitation, humidity, wind and fuel availability (Westerling et al., 2003), fire is a dynamic force shaping forest composition and is considered one of the most important natural disturbances in the coniferous forests of the western United States (US). Understanding these variables is important for determining how fire regimes may vary in response to climate change (Dale et al., 2001). One of the few ways we can learn about the interactions between fire and climate is to look at past fire regimes as a baseline against which to measure modern changes. Fire histories obtained through the examination and quantification of charcoal preserved in lake sediments are particularly useful because of their long temporal span. Unlike tree rings, which offer annual resolution but are generally age-limited to the past few hundred years, charcoal records preserved in lake sediments have the ability to reconstruct a fire history over millennia (Long et al., 1998). Charcoal records are also useful in that they can identify long-term shifts in fire regimes during periods of major climate change (Brunelle and Whitlock, 2003). To understand the fire ecology of …