More about forests in the Rocky Mountain West.
A symposium in Aspen, Colorado, last month highlighted the sweeping but not widely understood ways that human alternation of the climate is already disrupting the West’s forests. Some of the leading scientists discussed their findings and views at a Forests at Risk Symposium hosted by For the Forest, a local non-profit.
Particularly noteworthy was the presentation of Jim Worrall, a U.S. Forest Service scientist discussing research by himself and other USFS scientists on what an altered climate is doing and may well do to aspens – namely, eliminate this, our region’s most iconic tree, from most of its range in the West. The USFS’s Gerald Rehfeldt and two colleagues in 2009 published a study http://www.treesearch.fs.fed.us/pubs/33823 that used variables defining where aspens grow, three climate models, and three scenarios for future emissions of heat-trapping gases (one with medium-high levels and two with lower levels) to project future aspen distribution. Their work suggests that by around 2060, aspen will be eliminated from 40% to 48% of its current range with lower future emissions, and from 50% to 74% with medium-high emissions. At the symposium, Worrall correlated these projections with his own work on sudden aspen decline (SAD) – the precipitous, landscape-wide death of aspen stands across much of the West prompted by the heat and drought of the last decade. Worrall showed that SAD has occurred in the areas identified by Rehfeldt and others as where aspens are most vulnerable to climate change, and concluded that sudden aspen decline appears to be the beginning of the loss of the region’s aspens from human-caused climate change. A 13-minute video of Worrall’s presentation can be found here; it is highly recommended.
Another key presentation was by Philip van Mantgem, a U.S. Geological Survey scientist who with others has discovered a recent, widespread increase in “background” tree mortality in old forests across the West – tree deaths not caused by fires, insects, or other obvious disturbances. In his presentation, he linked the higher tree death rate to the hotter temperatures we already have experienced in the region. A video of his presentation is here.
The symposium was well summarized by the Aspen Times: Aspen symposium: Grim outlook for forests because of bugs disease, February 19, 2011.