One species of woody plant that’s been in decline on the National Elk Refuge for decades is showing some signs of bouncing back in northern parts of the preserve.
Aspen trees, a food source for wintering elk and other ungulates, need to reach a height of at least 8 feet to be impervious to browsing and to ensure a shot at reaching adulthood. A collaborative Montana State University-Elk Refuge study is now underway, and will attempt to quantify how many young aspens are positioned to survive and where they’re located, refuge biologist Eric Cole said.
“There’s some evidence that, at least on the extreme north end of the refuge, some aspen regeneration has been taking place,” Cole said.
“What we’re most interested in is the capacity of the stand to regenerate,” he said, “as measured by the number of young trees in the stand and their rate of height growth.”
Jenny Edwards, the graduate student heading the project, is assessing the makeup of 35 different tree stands spread out around the north end of the refuge.
“The measurements I take and the observations I note tell a story of browsing,” Edwards said in a refuge statement. “You can learn how an area has been used by wildlife.”
Southern portions of the 25,000-acre preserve weren’t included in the study because heavy browsing makes quick work of young trees, Cole said.
“The aspen stands on the south end of the refuge are a lost cause,” Cole said. “There’s no potential for regeneration.”
“Woody plant communities in general on the refuge are subject to high browsing,” he said. “What we found on the extreme north end of the refuge is the exception, not the rule.”
“Imperfect Pasture,” a 2004 book Cole co-authored with now-retired refuge biologist Bruce Smith, includes photos that illustrate just how extensively the refuge’s tree stands have declined.
“Willow plants were so reduced in height that they simply were no longer a dominant species across 95 percent of their present distribution on the south half of the refuge,” the biologists wrote.
Accounting for all woody plants, including willows, aspens and cottonwoods, there was an estimated 78 percent reduction, according to “Imperfect Pasture.”
Edwards’ research will help refuge managers understand why and to what extent aspens are recovering in the hillier, northern portions of the refuge, Cole said.
One explanation could be a recent decline in the percentage of the elk in the vicinity of the refuge that are eking out an existence foraging on native range. A larger and larger portion of the herd has relied on the refuge’s alfalfa pellet feed lines in recent years, Cole told the News&Guide last winter.
Management of aspens and other vegetation is prescribed in the 2007 interagency Bison and Elk Management Plan. The refuge’s upcoming Comprehensive Conservation Plan, expected this summer, also calls for a “sufficient level of aspen recruitment and maintenance of various class conditions,” the refuge’s statement said.