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05 Nov 2012: Reduced Snowpacks Allowing
Trees to Invade U.S. Mountain Meadows

Some mountain meadows in the U.S. Northwest are steadily disappearing as the effects of climate change have allowed trees to invade the ecosystemsin recent decades, a new study says. In an analysis of Jefferson Park, a 330-acre subalpine meadow complex in the Oregon Cascades once covered with grasses, shrubs and wildflowers, researchers found that tree occupation increased from 8 percent in 1950 to 35 percent in 2007, a rapid shift they say reflects a wider trend in many areas of the U.S. West. According to scientists, rising temperatures and a reduction in snowpack duration were critical factors in the invasion of mountain hemlocks in the meadow, saying that the extended growing season significantly increased chances of the trees’ survival. “Once trees become fully established, they tend to persist, and seed banks of native grass species disappear fairly quickly,” said Harold Zald, a research associate at Oregon State University’s College of Forestry and lead author of the study, published in the journal Landscape Ecology. “The meadows form an important part of forest biodiversity, and when they are gone, they may be gone forever.” While some have suggested that the meadow ecosystems may simply move up the mountain as the climate changes, the researchers suggest that in many cases the steep slopes and unstable soils will not support significant plant growth.

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