Tangled Trends for Temperate Rain Forests as Temperatures Tick Up

Climate change is altering growing conditions in the temperate rain forest region that extends from northern California to the Gulf of Alaska. Longer, warmer growing seasons are generally increasing the overall potential for forest growth in the region. However, species differ in their ability to adapt to changing conditions. For example, researchers with Pacific Northwest Research Station examined forest trends for southeastern and southcentral Alaska and found that, in 13 years, western redcedar showed a 4.2-percent increase in live-tree biomass, while shore pine showed a 4.6-percent decrease. In general, the researchers found that the amount of live-tree biomass in extensive areas of unmanaged, higher elevation forest in southern Alaska increased by as much as 8 percent over the 13-year period, contributing to significant carbon storage. Hemlock dwarf mistletoe is another species expected to fare well under warmer conditions in Alaska. Model projections indicate that habitat for this parasitic species could increase 374 to 757 percent over the next 100 years. This could temper the prospects for western hemlock—a tree species otherwise expected to do well under future climate conditions projected for southern Alaska. In coastal forests of Washington and Oregon, water availability may be a limiting factor in future productivity, with gains at higher elevations but declines at lower elevations.