Mountain meadows dwindling in the Pacific Northwest

Mountain meadows dwindling in the Pacific Northwest

02 November 2012

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USA– Some high mountain meadows in the Pacific Northwest are declining rapidly due to
climate change, a study suggests, as reduced snowpacks, longer growing seasons and other factors
allow trees to invade these unique ecosystems that once were carpeted with grasses, shrubs and

The process appears to have been going on for 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.

The findings of that research, which was funded by the Pacific Northwest Research Station of the USDA
Forest Service, were published in the journal Landscape Ecology.

The changes in Jefferson Park are representative of a larger force that is affecting not only this beautiful
meadow at the base of Mount Jefferson, scientists say, but many areas of 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.”

The meadow decline takes place over several decades, like the melting of glaciers. This also provides a 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

The study also found surprising variability of tree invasion even within the meadow, based on minor dips,
debris flows or bumps in the terrain that caused changes in snowpack and also left some soils wetter or
drier in ways that facilitated 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 balds” 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.



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