Yellowstone fires produce new trees, not meadows

  • Seedlings grow beneath charred trees in Yellowstone

    Michael Hofferber
 

Crouched over a metal screen like a gold rush prospector and peering through its grid at the forest floor, Cindi Persichetty calls out what she sees through each square-inch opening: "Line four: moss, moss, litter, seedling, seedling, seedling." Another Idaho State University graduate student, Mike O'Hara, sits on a log recording the findings on a clipboard.

The charred remains of a lodgepole pine loom above them, groaning in the morning breeze that rises off the Madison River in Yellowstone National Park. The forest floor is carpeted with thousands of bright green seedlings, each less than a foot high.

Directed by researchers Jay Anderson of Idaho State University and William Romme of Fort Lewis College in Durango, Colo., the monitoring seeks to answer the question of how fire affects the regeneration of lodgepole forests.

"Their thinking is that if the fire gets into the crown of the trees it will kill a lot more of the seeds and so you'd have less seedling density in those areas," Persichetty explains.

Five years of monitoring by Anderson, Romme and other scientists has documented an amazing recovery from the 1988 fires that consumed nearly 1 million of the 2.2 million acres of Yellowstone Park.

Vegetation in most burned areas has recovered quickly. Water flows increased in many streams without causing erosion as severe as some feared. Mammal populations have remained steady or are growing.

Lodgepole pine, which grows in vast stands throughout the western United States, has evolved to regenerate after a fire. Its cones are usually "serotinous," opening and dispersing their seeds when exposed to heat. But Yellowstone's storm of fires was so big and so hot that many wondered how well the lodgepole would recover.

"Even under conditions as extreme as in the summer of 1988, widespread holocaustic fires rarely consume entire landscapes," Anderson says.

Anderson found that lodgepole seedlings are common - up to 400 per acre - in the moderate burns. 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 burned.

"The Yellowstone fires are not likely to create vast meadows where forests stood in 1988," Anderson and Romme said 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 big impact on the Yellowstone ecosystem from the 1988 fire may turn out to be an upsurge of aspen. Anderson and Romme reported finding aspen seedlings in all their study sites, even where no aspen stands grew before the fire.

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 another Park Service biologist, Don Despain, author of Yellowstone Vegetation, most aspen reproduction in Yellowstone is by way of suckers, which are genetic clones that grow from the parent tree'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 explains. "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 today were once fed upon by mammoths, horses and camels."

Aspen seeds rarely germinate in Yellowstone because the seedlings are too small to compete with other vegetation and are very sensitive to even moderately dry conditions. They require plenty of sun and moisture to thrive. Despain and Rankin theorize that the 1988 fires produced the exact conditions aspen seeds needed: elimination of most of the competing vegetation, creation of large open spaces with plenty of sunshine, and leftover fire ash which helped increase the water-holding capacity of the soil.

The two agency biologists have begun monitoring 15 of the new aspen seedling sites as well as 10 sites with aspen suckers to compare success rates. And they are watching how aspen seedlings compete with lodgepole.

The seedlings that prevail will likely dominate the next generation of Yellowstone forests.

The writer free-lances from Shoshone, Idaho.

For more information, contact John Varley, chief of research, Yellowstone National Park, WY 82190-0168 (307/344-2203) and the Greater Yellowstone Coalition, P.O. Box 1874, Bozeman, MT 59771 (406/586-1593).

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