Yale University, environment 360: “Some mountain meadows in the U.S. Northwest are steadily disappearing as the effects of climate change have allowed trees to invade the ecosystems in recent decades, a new study says. In an analysis of Jefferson Park, a 330-acre subalpine meadow complex in 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 Universitys 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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