25 Apr 2010, 1:19pm
Ecology History Management Policy
by admin

Climate Changes and their Effects on Northwest Forests

Schlichte, Ken. 2010. Climate Changes and their Effects on Northwest Forests. Northwest Woodlands, Spring 2010.

Ken Schlichte is a retired Washington State Department of Natural Resources forest soil scientist. Northwest Woodlands Magazine [here] is a quarterly publication produced in cooperation with woodland owner groups in Oregon, Washington, Idaho and Montana.

Full text [here]

Selected excerpts:

Climate changes are always occurring, for a variety of reasons. Climate changes were responsible for the melting and retreat of the Vashon Glacier back north into Canada at the beginning of the postglacial Holocene Epoch around 11,000 years ago. Climate changes were also responsible for the warmer temperatures of the Holocene Maximum from around 10,000 to 5,000 years ago, the warmer temperatures of the Medieval Warm Period around 1,000 years ago and the coldest temperatures of the Little Ice Age during the Maunder Minimum around 300 years ago. These climate changes, the reasons for them and their effects on our Northwest forests are discussed below.

Forests soon became established on the glacial soil deposits left by the retreat of the Vashon Glacier, but some of these forests were later replaced by prairies and oak savannahs as temperatures increased during the Holocene Maximum. …

Forests began advancing into the South Puget Sound area prairies and replacing them as temperatures began decreasing following the Holocene Maximum. Native Americans began burning these prairies in order to maintain them against the advancing forests for their camas-gathering and game-hunting activities. Forest replacement of these and other Northwest prairies has proceeded rapidly since the late-1800s in the absence of these burning activities. …

The warmer temperatures and increased solar activity of the Medieval Warm Period were followed by a period of cooler temperatures and reduced solar activity known as the Little Ice Age. The coldest temperatures and lowest solar activity of the Little Ice Age both occurred during the Maunder Minimum from 1645 to 1715… The Dalton Minimum was a period of lower solar activity and colder temperatures from 1790 to 1820. Mount Rainier’s Nisqually Glacier reached a maximum extent in the last 10,000 years during the colder temperatures of the Maunder Minimum and the Dalton Minimum and then began retreating as Northwest temperatures warmed following the mid-1820s and the Dalton Minimum. Beginning in 1950 and continuing through the early 1980s the Nisqually Glacier and other major Mount Rainer glaciers advanced in response to the relatively cooler temperatures and higher snowfalls of the mid-century, according to the National Park Service. …

The National Climatic Data Center (Figure 3) indicates that annual temperatures in the Northwest Region (Washington, Oregon and Idaho) trended upward at a rate of 0.06 degrees Fahrenheit per decade from 1900 to 2000 for a total increase of 0.60 degrees Fahrenheit during the 20th century. The National Climatic Data Center also indicates that during the 20th century the Northwest Region’s annual precipitation increased by 10 percent and the summer precipitation increased by 28 percent.

The National Climatic Data Center (Figure 4) indicates that annual temperatures in the Northwest Region have trended downward at a rate of 0.95 degrees Fahrenheit per decade during the 10 years from 2000 to 2009.

Impacts of Climate Change on Washington’s Economy, published in 2006 for the Washington Department of Ecology and the Washington Department of Community, Trade and Economic Development, predicted that the Northwest will continue to warm approximately 0.50 degrees Fahrenheit each decade over the next several decades and that forest acres burned annually during the 2040s will be double the forest acres burned during an average 20th century year. This 2006 prediction contrasts with the National Climatic Data Center figure indicating that Northwest annual temperatures have actually been trending downward at a rate of 0.95 degrees Fahrenheit per decade during the 10 years from 2000 to 2009.

Wildfire problems and mountain pine beetle outbreaks increased significantly in Northwest forests during the 20th century and some have suggested that climate change is responsible, despite the fact that Northwest annual temperatures increased by only 0.60 degrees Fahrenheit during the 20th century and have been trending downward since 2000. Western Forest Health and Biomass Energy Potential, published in 2001 by the Oregon Department of Energy, gives the primary responsibility for increasing wildfire problems to 20th century fire control activities that allowed development of forest communities that are overstocked and too dense for the moisture and nutrient conditions of a particular site. These forest communities are also highly susceptible to mountain pine beetle outbreaks. Forest thinning experiments that began back in the 1960s in response to increasing mountain pine beetle outbreaks have indicated that thinning of dense overstocked stands minimizes the potential for outbreaks.

In summary, climate changes are always occurring for a variety of reasons, and Northwest forests have experienced a wide range of temperatures in the 11,000 years of the Holocene Epoch. Temperatures have been trending upward since the end of the Maunder Minimum in 1715, but Northwest annual temperatures trended upward only 0.60 degrees Fahrenheit during the 20th century. …

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