Mountain meadows may be disappearing
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November 2, 2012 |
 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
wildflowers.
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,
http://bit.ly/SBCohC.
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 survival.
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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