Area burned in alpine treeline ecotones reflects region-wide trends

Abstract

The direct effects of climate change on alpine treeline ecotones - the transition zones between subalpine forest and non-forested alpine vegetation - have been studied extensively, but climate-induced changes in disturbance regimes have received less attention. To determine if recent increases in area burned extend to these higher-elevation landscapes, we analysed wildfires from 1984-2012 in eight mountainous ecoregions of the Pacific Northwest and Northern Rocky Mountains. We considered two components of the alpine treeline ecotone: subalpine parkland, which extends upward from subalpine forest and includes a fine-scale mosaic of forest and non-forested vegetation; and non-forested alpine vegetation. We expected these vegetation types to burn proportionally less than the entire ecoregion, reflecting higher fuel moisture and longer historical fire rotations. In four of eight ecoregions, the proportion of area burned in subalpine parkland (3%-8%) was greater than the proportion of area burned in the entire ecoregion (2%-7%). In contrast, in all but one ecoregion, a small proportion (≤4%) of the alpine vegetation burned. Area burned regionally was a significant predictor of area burned in subalpine parkland and alpine, suggesting that similar climatic drivers operate at higher and lower elevations or that fire spreads from neighbouring vegetation into the alpine treeline ecotone.