Mountain Meadows In The Pacific Northwest Are Disappearing Because Of Climate Change, Study Says

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Meadows located high up in the mountains of the Pacific Northwest have been observed to be rapidly declining in recent years. New research is strongly suggesting that this is because of climate change.

As a result of reduced snowpacks, subsequent longer growing seasons, and a variety of other factors, trees have been invading these unique ecosystems. Trees replacing what had once been grasses, wildflowers, and shrubs.

It seems that the process has been going on throughout the last few decades, “but was highlighted in one recent analysis of Jefferson Park, a subalpine meadow complex in the central Oregon Cascade Range, in which tree occupation rose from 8 percent in 1950 to 35 percent in 2007.”

These changes have been observed throughout the Northwest though, not just Jefferson Park. And really they are just an example of the large changes occurring throughout the American West.

“We worry a lot about the loss of old-growth forests, but have overlooked declines in our meadows, which are also areas of conservation concern,” said Harold Zald, a research associate in the College of Forestry at Oregon State University and lead author of this study.

“The first awareness of declining meadows dates back to the 1970s, and we’ve seen meadow reduction at both high and low elevations,” Zald said. “Between climate change, fire suppression and invasive species, these meadows and all of the plant, animal and insect life that depend on them are being threatened.

“Once trees become fully established, they tend to persist, and seed banks of native grass species disappear fairly quickly,” he said. “The meadows form an important part of forest biodiversity, and when they are gone, they may be gone forever.”

Since the decline in meadows takes place over a timespan of decades, like melting glaciers; it functions as a clear “way to gauge long-term climate change,” Zald said. “Since the forces at work persist through seasonal, annual and longer patterns that are variably more wet, dry, hot or cold than average.”

“It takes a long time to melt a glacier or fill in a meadow,” he said. “It’s a useful barometer of climate change over decadal time periods.”

“In this study, it appears that snowpack was a bigger factor than temperature in allowing mountain hemlock tree invasion of Jefferson Park, a 333-acre meadow which sits at the northern base of Mount Jefferson, a towering 10,497-foot volcano northwest of Bend, Ore. Seedlings that can be buried by snow many months every year need only a few more weeks or months of growing season to hugely increase their chance of survival.”

The research also revealed an unexpected variability of tree invasion based on “minor dips, debris flows or bumps in the terrain.” These caused changes in the quality of the snowpack, leaving soils with varying levels of moisture that affected tree seedling survival.

“The process of tree invasion is usually slow and uneven,” Zald said. “But if you get all the conditions just right, some tree species can invade these meadows quite rapidly.”

“There’s some suggestion that alpine meadows may simply move higher up on the mountain in the face of a changing climate, Zald said, but in many cases slopes become too steep, and poor-quality, unstable soils are unable to harbor much plant life.”

“In other research in recent years, Zald said, he looked at meadows on lower-elevation mountains in the Oregon Coast Range — what are called ‘grass balda’ on the tops of some of the higher peaks, such as Mary’s Peak, the highest point in that range west of Corvallis, Ore. In a study of five Coast Range sites, Zald found that these ‘bald spots’ had declined by an average of 50 percent between 1950 and 2000.”

The findings were just published in the journal Landscape Ecology.

Source: Oregon State University

Image Credits: Harold Zald, courtesy of Oregon State University

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