OREGON STATE UNIVERSITY

Analysis outlines impacts of climate change on western Oregon

11/24/2009

CORVALLIS, Ore. – Snowpack at selected sites in the Oregon Cascade Range has already been cut in half over the past 77 years, despite no significant changes in precipitation, according to a new analysis of the impact of climate change on western Oregon.

The report, prepared by a group of researchers at Oregon State University, was done at the request of the Oregon Climate Change Research Institute. It outlined what is known about the physical, natural or socioeconomic impacts of past effects of regional climate change – and also cast an eye to the future.

The analysis found that temperatures in January, March and April have increased by almost four degrees since 1958 – spring is arriving earlier than it used to. Temperatures at other times of the year, however, have not changed much. These and other data are based primarily on observations at the H.J. Andrews Experimental Forest, a mid-elevation forest near Blue River similar to many areas of the Cascade Range and Coast Range in western Oregon. The Andrews Forest is supported by the U.S. Forest Service and the National Science Foundation.

Increased temperatures in the future may continue to take their toll on snowpack and springtime stream flows, the researchers said, but it’s less clear what the effects of climate change will be on conifers and other vegetation, some of which have the ability – to an extent – to adapt to changing conditions.

“What we’ve seen the most already, and will probably see even more in the future, is declining snowpacks and related effects on stream flows,” said Julia Jones, a professor of geosciences at OSU and coordinator of the report.

“Of some interest, however, is that these forests, especially older Douglas-fir, seem to be able to respond to water availability and drought by closing down their photosynthesis,” Jones said. “To some degree, they are opportunistic and will use water when it’s available. Some of them are 500 years old and have already lived through a lot of climate variability, they get knocked around all the time.”

It’s not certain, the researchers said, how far that resiliency can be pushed before it starts causing forest health or mortality problems. Increasing winter temperatures can favor tree growth in the following summer, while less summer water availability might decrease it – offsetting mechanisms that could explain why no significant changes in tree growth rates has been observed in the Andrews Forest in the past century, despite changes in temperature. And at least in this forest, there has been no increase in tree mortality, as has been observed in some other western forests.

Among the findings of the analysis:

  • Despite increasing temperatures, no significant changes in precipitation or wind have occurred at the Andrews Forest since the 1970s, although there is considerable variation dictated largely by the Pacific Decadal Oscillation, a periodic shift in climate patterns.
  • A projected temperature increase of 4-5 degrees in the future could mean increases of more than 11 degrees in some terrain and elevations, which respond quite differently than the overall average.
  • Extreme floods in the future will probably depend more on unusual weather events than trends in average climate conditions.
  • Conifers will continue to persist at forests similar to the H.J. Andrews at least through the year 2100, given expected scenarios of temperature, fire and carbon dioxide concentrations. Hardwoods may increase in some areas of the Willamette Valley.
  • Only spring stream flow has changed much in the past 50 years, possibly explained by higher water use by conifers.

Socioeconomic impacts are difficult to predict, the report suggested. Farm, forest and ranch owners may be disproportionately affected by changes in the resources on which they depend for income. On the other hand, they might profit by the emergence of a carbon-offset market under cap-and-trade legislation.

Forest management will also have to adapt to changing conditions, the researchers said. Young forest plantations use up to 70 percent more water in summer than old-growth forests, possibly exacerbating summer drought. And fuel treatments in forests to reduce fire risk may also reduce carbon storage potential.

This analysis focused primarily on western Oregon, and other work will continue to develop a broader understanding of statewide climate impacts. It’s fortunate, Jones said, that the H.J. Andrews Forest, a part of the nation’s Long Term Ecological Research program, has exceedingly long and diverse records to provide data on how the environment is changing.