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Living on the edge: Trailing edge forests are at risk

Date: April 12, 2019

The chances of converting from a forest to non-forest landscape may be increasing with the combination of climate change and stand-replacing fire


Trailing edge forest Southern Rockies ecoregion
Fig. 7. Expected fire severity, were a fire to occur under extreme weather conditions, for the Colorado Plateau, AZ–NM Mountains, and Apache Highlands ecoregions. (Figure credit Ecosphere Volume 10(3) Article e02651
Climate change will influence ecological systems across the planet, including expected range shifts in forest biomes. As the climate continues to warm, trailing edge forests have the potential to experience abrupt conversions to non-forest. Such conversions are of particular concern in the semi-arid and fire-prone Intermountain Region of the western United States where many communities rely on forests for clean water, timber, and recreation. Yet, broad-scale conversions to non-forest are likely to be gradual in the absence of stand-replacing disturbances such as severe fire. Our study explicitly evaluated the spatial correspondence between trailing edge forest and stand-replacing fire. In doing so, we characterized areas that are primed for change and have the potential for fire-facilitated conversion from forest to non-forest. We found that 6.6 percent of current forest in the intermountain United States is at risk of such conversions, though this varied among ecoregions. Although this value (6.6 percent of forest) may not outwardly seem alarming, we note that this is a conservative estimate. When we incorporated fire severity predictions under extreme fire weather in the southwestern United States, we found that 30 percent of forest is at risk of fire-facilitated conversion to non-forest. Recent studies in the southwestern United States and elsewhere have documented such conversions. Given our estimate that nearly 36 percent of forest area in the intermountain United States will be trailing edge forest by mid-century, other non-fire disturbances such as drought, insect outbreaks, and their interactions may put trailing edge forests at further risk.

*See gallery above for additional photos and figures

Key Findings

  • In the southwestern United States, we found that 30 percent of forest is at elevated risk of fire-facilitated conversion to non-forest when assuming that fire burns under extreme weather conditions.

  • Such conversions are of particular concern in the semi-arid and fire-prone Intermountain Region of the western United States where many communities rely on forests for clean water, timber, and recreation

  • Explicit attention to both climate and disturbance is necessary to understand how the distribution of forests will respond to climate change

Featured Publications

Parks, Sean A. ; Dobrowski, Solomon Z. ; Shaw, John D. ; Miller, Carol L. , 2019


Principal Investigators - External: 
Solomon Z Dobrowski - W.A. Franke College of Forestry and Conservation - College of Forestry & Conservation: The University of Montana
Research Location: 
Intermountain western United States