...of house and home.
Elk devouring future of beavers, wetlands
By Theo Stein
Denver Post Staff Writer
Rocky Mountain National Park - The industrious beaver, nature's supreme wetlands engineer, is having a tough time recolonizing its former strongholds.
During the early 20th century, hundreds of the large rodents paddled through ponds of their own making in the park's high valleys that flank the Continental Divide.
But recent studies suggest beavers now number no more than several dozen.
Trapping once was a major cause of the beaver's decline in Rocky Mountain National Park. But now beavers have run into a different problem.
Elk.
Since the 1960s, the booming elk population has become a park institution, beloved by millions of visitors who thrill to frosty autumn bugles and the jousts of bulls in rut.
But the elk herds' incessant browsing on twigs and shoots has, over decades, converted stands of tall willow to dry grassland, punctuated by stunted hedgelike willow clumps that are useless as beaver food.
"Beaver are gone from probably 50 percent of our streams," said Mark McKinstry, a biological scientist with the U.S. Bureau of Reclamation in Salt Lake City. "And in another 30 percent, there are so few they perform no ecologic function."
The removal of beavers "has been one of the biggest negative impacts we've had on the landscape of the Western United States," he added.
Biologists have long applauded the beaver's instinctive need to build shifting wetlands, which provide flowers for butterflies, cool water for trout and ample browse for gangly, water-loving moose.
Now, a study underway in the Rocky Mountain National Park's Kawuneeche Valley is demonstrating that beavers are also critical managers of the West's most precious resource - water. Some scientists even believe beavers can be a defense against climate change.
"We're trying to quantify their benefits to help people understand where beaver are valuable," said Bruce Baker, a wildlife biologist with the U.S. Geologic Survey.
Elk stymie recovery
Park officials say the Estes Valley elk herd, which has ballooned to about 3,000, has pared back willow stands by 20 percent and aspen stands by 40 percent. And that has reduced the forage available for beavers.
"Trapping initiated the beaver decline, but it appears elk browsing is preventing their recovery," said Baker, who is studying the relationship between beavers and elk.
Meanwhile, Park Service biologists are developing a list of alternatives that would let them manage elk numbers and allow aspen and willow to recover. Preliminary ideas include killing elk with sharpshooters, fencing off wetland areas, hazing herds with teams of horsemen and dogs - even reintroducing wolves.
"The bottom line: The vegetation needs to be protected," said Therese Johnson, a Park Service biologist who is heading up the elk study.
Officials hope to publish a draft environmental impact statement by the end of the year and make a final decision on the elk-management plan by the end of 2005.
Whither the willow?
On a recent spring day in Moraine Park, the results of elk overpopulation are starkly apparent: Dead willow clumps - their tangled, broken stems blasted gray by the wind - stretched across the dry plain.
These ranks of bleached skeletons are all that remain of an expansive wetland where, 40 years ago, scores of beaver dams lifted the Big Thompson River out of its channel and, in hundreds of streams and rivulets, sent its waters trickling across the waterlogged valley.
But after trapping removed the beavers, their dams eventually failed and the Big Thompson fell back into three main channels. With no underground water to sustain them and hordes of elk chomping their branches, the willow declined sharply.
Wetlands created by beaver dams act as giant sponges, absorbing spring runoff and releasing it slowly during dry periods to maintain more even stream flows throughout the year. By suppressing willow, elk are preventing beavers from restoring Moraine Park to its naturally soggy self, experts said.
Overbrowsing has also limited beaver recovery in Horseshoe Park and the Kawuneeche Valley on the Colorado River, although that problem may be from a combination of elk and a smaller number of moose, Baker said.
Tree-pruning styles differ
Baker said the combined effect of beaver cutting and elk browsing creates a feedback mechanism that reduces both beaver and willow populations.
One reason is because of the way the two animals feed.
Beaver nip off larger-diameter willow stems at ground level because it provides them with more of the bark that they eat. In response, willows generate a single stem to replace the eaten one, which beavers will let grow until it becomes large enough to be worth the effort of harvesting.
"By contrast, elk browse on the tips only," said Baker, pointing to one shrubby elk victim.
The plant responds by sending out more shoots. Constant browsing by elk keeps willow tips at mouth level. That's good for elk, but it prevents the new shoots from growing large enough to be beaver food.
To study what would happen if willow were protected from elk, researchers have constructed five fenced enclosures inside Moraine Park. The trees rebounded so strongly that beavers have since colonized four of the five pens and built dams inside them.
Baker said the data will help the park better understand how to manage beavers, elk and willows.
As the elk population continues to grow, the problem may be spreading to other parts of the park.
Just over a low hill to the south, Hollowell Park still has a flooded willow bottom inhabited by a beaver colony - one transplanted from Denver. Baker is not sure why the tiny valley has avoided the attention of elk, but willows on the edge of the wetland show clear signs of elk abuse.
Studies in Yellowstone and Glacier national parks have shown elk are limiting beaver recovery there.
The regional effects are hard to gauge but are certainly large, said McKinstry, who has studied current and historical beaver range across Wyoming since 1992. He estimates the loss of beavers has probably cut Wyoming's annual production of ducks by half a million birds. "And that's just one species," he said.
Keeping things flowing
Another ongoing study in Rocky Mountain National Park has shown just how effective beavers can be at cushioning the impact of severe drought.
During 2002, Colorado State University researcher Cherie Westbrook set up a grid of groundwater wells to measure how large an area was kept moist by a single beaver dam across the upper Colorado River. Westbrook found that the dam raised groundwater levels behind the dam next to the pond, but it also kept a large area downstream of the dam wet.
In 2003, a March blizzard contributed to record spring snowmelt that blew out the beaver dam. That summer, the wet meadows dried up.
Westbrook, who is studying beavers for her doctoral dissertation, noted that in 2002, the Grand Ditch, which carries 30 percent of the valley's snowmelt east to the Front Range, was operational. In 2003, the snowmelt caused the ditch to rupture and fail.
"So during the driest year on record, there was more water in the wetlands and we had larger areas inundated than during 2003, which saw the highest flows on record," she said. "It seems that beaver can mitigate the effect of water diversions."
A change in the weather
And as evidence of global warming mounts, some top beaver researchers think America's largest rodent can provide a vital brake against the local impacts of climate change - if people would only let them.
Beaver-created ponds and terraced wetlands act as strings of sanctuaries in times of extended warmth or drought, McKinstry said.
"Everything they do is geared towards moderating their environment and making it stable," McKinstry said. "They create habitats that are reliable and predictable for other species."
Yellowstone wolf biologist Doug Smith, who studied beavers for his dissertation, said the wetlands that beavers create serve as "escape terrain" for a range of animals in times of heat stress.
"The ponds and the vegetation that grows around them create cooler water and shade for fish, amphibians and other animals to get out of the heat," he said.
Beavers have a larger effect in areas that are inherently drier, Baker said. Given enough food, beavers can take a desert stream and create a little oasis, he said.
"If you place global warming in that context, some places that are wetter now are likely to become drier," he said. "Beaver will have larger impact on those areas."
Elk devouring future of beavers, wetlands
By Theo Stein
Denver Post Staff Writer
Rocky Mountain National Park - The industrious beaver, nature's supreme wetlands engineer, is having a tough time recolonizing its former strongholds.
During the early 20th century, hundreds of the large rodents paddled through ponds of their own making in the park's high valleys that flank the Continental Divide.
But recent studies suggest beavers now number no more than several dozen.
Trapping once was a major cause of the beaver's decline in Rocky Mountain National Park. But now beavers have run into a different problem.
Elk.
Since the 1960s, the booming elk population has become a park institution, beloved by millions of visitors who thrill to frosty autumn bugles and the jousts of bulls in rut.
But the elk herds' incessant browsing on twigs and shoots has, over decades, converted stands of tall willow to dry grassland, punctuated by stunted hedgelike willow clumps that are useless as beaver food.
"Beaver are gone from probably 50 percent of our streams," said Mark McKinstry, a biological scientist with the U.S. Bureau of Reclamation in Salt Lake City. "And in another 30 percent, there are so few they perform no ecologic function."
The removal of beavers "has been one of the biggest negative impacts we've had on the landscape of the Western United States," he added.
Biologists have long applauded the beaver's instinctive need to build shifting wetlands, which provide flowers for butterflies, cool water for trout and ample browse for gangly, water-loving moose.
Now, a study underway in the Rocky Mountain National Park's Kawuneeche Valley is demonstrating that beavers are also critical managers of the West's most precious resource - water. Some scientists even believe beavers can be a defense against climate change.
"We're trying to quantify their benefits to help people understand where beaver are valuable," said Bruce Baker, a wildlife biologist with the U.S. Geologic Survey.
Elk stymie recovery
Park officials say the Estes Valley elk herd, which has ballooned to about 3,000, has pared back willow stands by 20 percent and aspen stands by 40 percent. And that has reduced the forage available for beavers.
"Trapping initiated the beaver decline, but it appears elk browsing is preventing their recovery," said Baker, who is studying the relationship between beavers and elk.
Meanwhile, Park Service biologists are developing a list of alternatives that would let them manage elk numbers and allow aspen and willow to recover. Preliminary ideas include killing elk with sharpshooters, fencing off wetland areas, hazing herds with teams of horsemen and dogs - even reintroducing wolves.
"The bottom line: The vegetation needs to be protected," said Therese Johnson, a Park Service biologist who is heading up the elk study.
Officials hope to publish a draft environmental impact statement by the end of the year and make a final decision on the elk-management plan by the end of 2005.
Whither the willow?
On a recent spring day in Moraine Park, the results of elk overpopulation are starkly apparent: Dead willow clumps - their tangled, broken stems blasted gray by the wind - stretched across the dry plain.
These ranks of bleached skeletons are all that remain of an expansive wetland where, 40 years ago, scores of beaver dams lifted the Big Thompson River out of its channel and, in hundreds of streams and rivulets, sent its waters trickling across the waterlogged valley.
But after trapping removed the beavers, their dams eventually failed and the Big Thompson fell back into three main channels. With no underground water to sustain them and hordes of elk chomping their branches, the willow declined sharply.
Wetlands created by beaver dams act as giant sponges, absorbing spring runoff and releasing it slowly during dry periods to maintain more even stream flows throughout the year. By suppressing willow, elk are preventing beavers from restoring Moraine Park to its naturally soggy self, experts said.
Overbrowsing has also limited beaver recovery in Horseshoe Park and the Kawuneeche Valley on the Colorado River, although that problem may be from a combination of elk and a smaller number of moose, Baker said.
Tree-pruning styles differ
Baker said the combined effect of beaver cutting and elk browsing creates a feedback mechanism that reduces both beaver and willow populations.
One reason is because of the way the two animals feed.
Beaver nip off larger-diameter willow stems at ground level because it provides them with more of the bark that they eat. In response, willows generate a single stem to replace the eaten one, which beavers will let grow until it becomes large enough to be worth the effort of harvesting.
"By contrast, elk browse on the tips only," said Baker, pointing to one shrubby elk victim.
The plant responds by sending out more shoots. Constant browsing by elk keeps willow tips at mouth level. That's good for elk, but it prevents the new shoots from growing large enough to be beaver food.
To study what would happen if willow were protected from elk, researchers have constructed five fenced enclosures inside Moraine Park. The trees rebounded so strongly that beavers have since colonized four of the five pens and built dams inside them.
Baker said the data will help the park better understand how to manage beavers, elk and willows.
As the elk population continues to grow, the problem may be spreading to other parts of the park.
Just over a low hill to the south, Hollowell Park still has a flooded willow bottom inhabited by a beaver colony - one transplanted from Denver. Baker is not sure why the tiny valley has avoided the attention of elk, but willows on the edge of the wetland show clear signs of elk abuse.
Studies in Yellowstone and Glacier national parks have shown elk are limiting beaver recovery there.
The regional effects are hard to gauge but are certainly large, said McKinstry, who has studied current and historical beaver range across Wyoming since 1992. He estimates the loss of beavers has probably cut Wyoming's annual production of ducks by half a million birds. "And that's just one species," he said.
Keeping things flowing
Another ongoing study in Rocky Mountain National Park has shown just how effective beavers can be at cushioning the impact of severe drought.
During 2002, Colorado State University researcher Cherie Westbrook set up a grid of groundwater wells to measure how large an area was kept moist by a single beaver dam across the upper Colorado River. Westbrook found that the dam raised groundwater levels behind the dam next to the pond, but it also kept a large area downstream of the dam wet.
In 2003, a March blizzard contributed to record spring snowmelt that blew out the beaver dam. That summer, the wet meadows dried up.
Westbrook, who is studying beavers for her doctoral dissertation, noted that in 2002, the Grand Ditch, which carries 30 percent of the valley's snowmelt east to the Front Range, was operational. In 2003, the snowmelt caused the ditch to rupture and fail.
"So during the driest year on record, there was more water in the wetlands and we had larger areas inundated than during 2003, which saw the highest flows on record," she said. "It seems that beaver can mitigate the effect of water diversions."
A change in the weather
And as evidence of global warming mounts, some top beaver researchers think America's largest rodent can provide a vital brake against the local impacts of climate change - if people would only let them.
Beaver-created ponds and terraced wetlands act as strings of sanctuaries in times of extended warmth or drought, McKinstry said.
"Everything they do is geared towards moderating their environment and making it stable," McKinstry said. "They create habitats that are reliable and predictable for other species."
Yellowstone wolf biologist Doug Smith, who studied beavers for his dissertation, said the wetlands that beavers create serve as "escape terrain" for a range of animals in times of heat stress.
"The ponds and the vegetation that grows around them create cooler water and shade for fish, amphibians and other animals to get out of the heat," he said.
Beavers have a larger effect in areas that are inherently drier, Baker said. Given enough food, beavers can take a desert stream and create a little oasis, he said.
"If you place global warming in that context, some places that are wetter now are likely to become drier," he said. "Beaver will have larger impact on those areas."
