|
|
|
|
|
|
|
|
|||||||||||||
|
|
|
|
|
|
|
||||||||||||||
|
|
|
|
|
|
|||||||||||||||
|
|
|
|
|
|
|||||||||||||||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|  The pace of a forestAnd so we burned in 1988 in Yellowstone, about which volumes have been written. And in 2000, most notably in New Mexico, Idaho and Montana's Bitterroot valley. And in 2001, wildfire in low-elevation forests came close enough to Bozeman for charred needles to rain on the town's sidewalks."This era of large fires we're now in started in '85 or '86 in California," mused Don Despain, a plant ecologist at the USGS Northern Rocky Mountain Science Center in Bozeman. "Ever since there have been areas in the West with really big fires. We pass it around." Something else uncovered in Yellowstone suggests that regional forests could continue their relay with the fire baton: Fires in the lower elevation forests-the Douglas fir zone between 5,000 and 7,000 feet-became less frequent after the 1880s. Fuels have built up to unprecedented levels in the last 100 years, said MSU ecology associate professor Andy Hansen.
But there's more, he argued. Within that same time period, the Douglas fir forests in the Yellowstone area have expanded and become more dense. Historical photos show fir trees encircling a remote cabin where 50 years ago they stood back. But the best proof comes from aerial photographs snapped by Forest Service employees flying the same transects in the Greater Yellowstone area from the 1930s until the present. Scott Powell and a team of other MSU graduate students lean over these photographs. The squares they draw show trees where previously there were none and stands thicker than they once were. Even an untrained eye can see change, which Powell said averages about 3.7 percent from 1971 to 1999 in the northern third of the Greater Yellowstone Ecosystem. They know from fieldwork that some, but not most, is regeneration after fires. Change is more pronounced at lower elevation treeline (below 6,000 feet). There Powell and his team have documented up to a 7 percent increase in tree growth on southerly aspects. Compound that over 100 years and forests in some areas could expand by 25 percent, Hansen said.
"On the pace of a forest, this is a dramatic change, if you think from 150 years back to when fires became less frequent to 50 or 100 years into the future," Hansen said. Why the conifers have crept down the mountainside and marched onto grasslands hasn't been answered. The effects of fire exclusion, livestock grazing and global climate change are possible hypotheses. Why it matters is a more pressing question to Hansen, who last year watched a wildfire in the Douglas fir zone burn to within 200 yards of his rural home. As Douglas firs have moved downslope, rural homes have moved up them, Hansen said, creating a so-called urban interface with heavy fuel loads. New homes have increased fourfold in the Greater Yellowstone Ecosystem since 1970. Many, like Hansen's, are right in the path of the wildfires that are bound to come. No doubt opinions about how to manage these forests to protect lives and property will differ. Page 1 2 3 Next |
