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Living on the Edge: Trailing Edge Forests Are at Risk

Photo of An example of a trailing edge forest in the southern Rocky Mountains.
An example of a trailing edge forest in the southern Rocky Mountains. Snapshot : Forests are an incredibly important resource across the globe, yet they are threatened by climate change through stressors such as drought, insect outbreaks, and wildfire. Trailing edge forests, those areas expected to experience range contractions under a changing climate, are of concern because of the potential for abrupt conversion to non-forest. However, broad-scale forest die-off and range contraction in trailing edge forests are unlikely to occur over short timeframes (less than 25–50 years) without a disturbance catalyst such as wildfire. As such, explicit attention to both climate and disturbance is necessary to understand how the distribution of forests will respond to climate change.

Principal Investigators(s) :
Parks, Sean A. Shaw, John D.
Research Location : Intermountain West, USA
Research Station : Rocky Mountain Research Station (RMRS)
Year : 2019
Highlight ID : 1561


​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 U.S. 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. A USDA Forest Service study explicitly evaluated the spatial correspondence between trailing edge forest and stand-replacing fire. It characterized areas that are primed for change and have the potential for fire-facilitated conversion from forest to non-forest. The scientists found that 6.6 percent of current forest in the intermountain U.S. is at risk of such conversions, though this varied among ecoregions. Although this value (6.6 percent of forest) may not outwardly seem alarming, the scientists note that this is a conservative estimate. When they incorporated fire severity predictions under extreme fire weather in the southwestern United States, they found that 30 percent of forest is at risk of fire-facilitated conversion to non-forest. Recent studies in the southwestern U.S. and elsewhere have documented such conversions. Given their estimate that nearly 36 percent of forest area in the intermountain U.S. 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.

Forest Service Partners

External Partners

  • University of Montana

Program Areas