|Yellowstone: The Next Generation
by Michael Hofferber
Copyright © 1994. All rights reserved.
Graduate student Cindi Persichetty crouched over the metal screen like a gold rush prospector, peering through its grid at the forest floor below.
"Line four. Moss, moss, litter, seedling, seedling, seedling," Persichetty called out. Her partner, Mike O'Hara, sat quietly and marked the findings on a clipboard.
The charred remains of a lodgepole pine forest loomed above them, groaning in the morning breeze wafting up from the Madison River in Yellowstone National Park.
"We've been monitoring 50-meter transect lines in 12 locations throughout the park where lodgepole pine forests burned in 1988," Persichetty explained.
"Within each one we located an area of moderate burn in which the fire didn't kill everything on the trees and another area nearby where there was a canopy burn and it did get up into the crown. A third transect was established in an unburned area as a control sample," she noted.
Five years of monitoring by Anderson, Romme and other scientists have documented an amazing recovery from the 1988 fires that burned nearly 1 million acres of the 2.2-million-acre Yellowstone National Park. Vegetation in most burned areas came back quickly and vigorously, water flow increased in many streams but erosion has been less than was feared, and mammal populations have remained steady or are growing.
The lodgepole pine, which grows in vast stands throughout the western U.S., is uniquely adapted for regeneration following a fire. Its cones are usually "serotinous," meaning they open and disperse their seeds when exposed to heat. Scientists knew the lodgepole was well adapted to reoccurring fire, but Yellowstone's 1988 fire was so big and so hot there was some question about how well they would recover.
"Even under conditions as extreme as those in the summer of 1988, widespread holocaustic fires rarely consume entire landscapes," Anderson pointed out. "Such was the case in Yellowstone, where even the worst fires were influenced by local winds, fuel availability and topography."
Anderson's monitoring of moderate burns and severe burn areas has demonstrated that lodgepole seedlings are much more common (4-24 times greater) in the lesser burns. In some moderate burns his study teams counted up to 400 seedlings per square meter. But lodgepole regeneration is also occurring in the most severe burns and the density of seedlings in all but four of the transects is more than sufficient to replace the stands of trees that were burned.
"The Yellowstone fires are not likely to create vast meadows where forests stood in 1988," Anderson and Romme stated in their report to the First Biennial Scientific Conference on the Greater Yellowstone Ecosystem last year. "We suspect that the majority of the park's burned areas will be characterized by extensive stands of evenly aged forests, much like the pattern in evidence after the fires of the early 1800s."
The biggest long-term change in the Yellowstone ecosystems following the 1988 fire probably won't be the absence of forests, but the prevalence of aspen. Anderson and Romme reported finding aspen seedlings in all their study sites, even in areas where no aspen stands stood before the fire. And Roy Rankin, a National Park Service biologist, has reported aspen seedling densities ranging from 1 to 1,000 per square meter in burn areas throughout Yellowstone.
According to research biologist Don Despain, author of "Yellowstone Vegetation" (Roberts Rinehart, 1992), most aspen reproduction in Yellowstone is by way of suckers, which are genetic clones that grow from the parent plant's lateral root system.
"In Yellowstone, it is not unreasonable to assume that many of the clones present today started as the glaciers retreated, 12,000 to 14,000 years ago," he explained. "If this is the case, the aspen we see now have lived through a lot of climatic and environmental changes. It is conceivable that the aspen clones being browsed by deer and elk todays were once fed upon by mammoths, horses and camels."
Aspen seeds rarely germinate in Yellowstone because they are too small to compete with other vegetation and they are very sensitive to even moderately dry conditions. They require both plenty of sun and lots of moisture to thrive.
Despain and Rankin have theorized that the 1988 fires produced the exact conditions aspen seeds needed to germinate. The fires eliminated most of the competing vegetation, created large open spaces with plenty of sunshine, and the leftover fire ash helped increase the water holding capacity of the soil.
The two National Park Service biologists have begun monitoring 15 of the new aspen seedling sites as well as 10 sites with aspen suckers to compare their development. And they are keeping a close watch on sites where aspen seedlings are competing with lodgepole. The seedlings that prevail in that competition will likely dominate the next generation of Yellowstone forests.
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Year of the Fires
The Story of the Great Fires of 1910