Influence of late Holocene climate and wildfire on mammalian community composition in the northern Rocky Mountains (USA)

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Over the last half century, the Rocky Mountains have experienced increasing temperatures, more frequent droughts, and remarkable increases in wildfire: trends that are expected to continue. While the consequences of ongoing climate and fire regime change for this region are uncertain, previous research suggests that the combination of more frequent fire with changing climate may lead to abrupt changes in vegetation, causing downstream effects including altering mammal communities. Small mammals, in particular, are more habitat-specific and less able to move great distances in response to habitat disturbance. Reconstructing how these ecosystems have responded to climate and fire regime change in the past can reveal underlying dynamics that enable us to anticipate how they will react to future changes. Although there has been substantial research on fire-climate-vegetation relationships, the long-term impacts of fire on small mammal communities are not well characterized. Here, we use mammalian fossils from Waterfall Locality, a fossil packrat midden in northeastern Yellowstone National Park spanning ~3,400 to 250 calendar years before present (cal YBP), to reconstruct mammal diversity (species richness, evenness, and relative abundance) through time and to explore whether changes in diversity and community composition were related to climate and fire regime. We evaluate reconstructed wildfire activity from sedimentary charcoal as well as seven modeled climate variables (mean annual temperature, minimum winter temperature, maximum summer temperature, temperature seasonality, mean annual precipitation, mean summer precipitation, and precipitation seasonality). We find evidence that both summer precipitation and wildfire contributed to small mammal community turnover. Higher summer precipitation was associated with higher proportions of closed-habitat mammals and lower proportions of open habitat mammals. Elevated levels of wildfire activity near the site from ~2,200 – 1,800 cal YBP likely also contributed to this change in closed- versus open-habitat mammals around 1,600 cal YBP. Waterfall Locality represents a ~3,400-year record of mammal diversity in lower montane forests of the northern Rockies, analyses of which provide context for predicting future changes to the mammal community in this region.

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