Over the next century, global warming could boost forest growth in the Pacific Northwest, a new study has found.
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Warming temperatures could lead to a significant increase in the productivity of high-elevation forests in the region, researchers at Oregon State University and the Forest Service's Pacific Northwest Research Station found. But forests at lower elevations, which in recent years have produced more than 80 percent of the region's timber harvest, could face a decline in growth.
Forests and their potential growth may play a significant role in future efforts to reduce the effects of climate change and in the use of credits for reducing carbon dioxide.
Overall, forest productivity could increase about 7 percent annually in forests west of the Cascade Range and 20 percent in forests east of them under one scenario that researchers said largely reflects current trends of energy use, globalization and economic growth. However, the study did not take into account management practices, disease, insects and fire, which can affect productivity and could also be affected by climate change.
"There's a lot of variability here, depending on which climate scenario turns out to be most accurate and what policy changes are made as a result," OSU professor Darius Adams said in a statement. "And there are dramatic differences in forest regions and elevations. Clearly the forest growth is likely to increase the most at higher elevations, but it's worth noting that those forests never had very high growth rates to start with."
The study, published in Forest Ecology and Management, showed that any increase in future temperatures could lead to an overall increase in forest productivity in the Pacific West. Increases in high-elevation forest productivity were partially offset by probable declines in lower-elevation forest productivity.
The results, based on computer modeling, would be most pronounced in Washington, where high-elevation forests could see their productivity increase from 35 percent to 500 percent, according to the study.
In Oregon, higher elevations might see forest growth increases of 9 to 75 percent. Low-elevation Oregon forests could see declines in forest growth of 1 to 3 percent a year, which could have a substantial long-term impact if trees are being managed for timber harvest.
The researchers said the climate scenarios they used showed temperature increases from 1 to 8 degrees but had widely varying precipitation projections. The models showed that increases in forest growth at higher elevations could increase carbon sequestration for those areas, but they did not include potential changes in fire frequency and severity, which can increase with greater forest growth.
The combination of tree mortality and declining future growth on private timberlands could lead to concerns about lower harvest levels and reduced carbon sequestration in the future.
The study is now being extended to coastal Alaska, the researchers said, where length of growing season is likely to be a more important factor than water availability, which was a large factor in much of Oregon and Washington.
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