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Study measures condition of aspen stands

06_25_14_AspenStudy_ArticleMaybe it’s their shimmering leaves rustling in the summer breeze. Perhaps it’s their striking yellow brilliance in the autumn light. Regardless, aspen trees are loved by people for their aesthetic qualities. But as widely appreciated as they are by human populations, quaking aspen forests provide important breeding, foraging, and resting habitat for a variety of birds and mammals.

June 25, 2014

Maybe it’s their shimmering leaves rustling in the summer breeze. Perhaps it’s their striking yellow brilliance in the autumn light. Regardless, aspen trees are loved by people for their aesthetic qualities. But as widely appreciated as they are by human populations, quaking aspen forests provide important breeding, foraging, and resting habitat for a variety of birds and mammals.

The northern hills of the National Elk Refuge are dotted with aspen, but little research has been done to document the ongoing health and vibrancy of the stands. Aspen have been declining throughout the West over the past few decades, causing concern among wildlife managers because of the importance of the species to wildlife. Whether it’s through providing hiding cover, thermal protection and summer shade, a source of food, or a site for nesting birds, aspen communities meet diverse habitat needs for many animals. 

This month, a graduate student from Montana State University is working with U.S. Fish and Wildlife Service biologists to collect baseline data at the National Elk Refuge, documenting aspen age classes and calculating the amount of browsing by ungulates in relation to their distance from supplemental feeding areas. 

Jenny Edwards, a teacher from Casper, Wyoming is working towards a Masters of Science in Science Education degree. Her graduate school capstone project will capture aspen stand structure in 35 sites on the Refuge. Edwards is using GIS information to locate known Refuge aspen stands, classify the height of the trees within a designated plot, and measure both the tallest browsed stem and the highest base on the current year’s growth. “The measurements I take and the observations I note tell a story of browsing,” Edwards explains. “You can learn how an area has been used by wildlife.” Browse line refers to the range of lower stripped and eaten-back stems, indicating the height reached in feeding by ungulates like elk, deer, and moose. Saplings that are 8 feet or taller are less vulnerable to damage and have a greater chance of becoming adult trees. 

While it may be unclear to Edwards why some stands break up and die when others remain stable, the information she’s collecting will identify trends and help track changes in the landscape and its use. 

There is increasing concern that in the West, poor quaking aspen regeneration may in part be due to wildlife overbrowsing of saplings. Where browsing pressure is heavy, ungulates can limit quaking aspen regeneration before the shoots grow to adult height. To provide for quaking aspen regeneration in such areas, a surplus of new saplings needs to grow so that even after browsing animals use the area, enough new growth remains to attain adult height. 

The most common method of regeneration in aspen is through root sprouting. As a fire adapted species, aspen can be stimulated to send up new shoots after a disturbance. However, areas that have large elk populations may see little growth of new shoots even after large-scale wildfires because of intense browsing. In these areas, quaking aspen saplings may require protection from browsing. 

The Bison & Elk Management Plan, as well as the Refuge’s upcoming Comprehensive Conservation Plan, addresses the need for a sufficient level of aspen recruitment and maintenance of various class conditions. 

While in the field, Edwards is also noting the bird communities using the aspen stands. A diverse array of birds benefit from aspen by using them as feeding, hiding, and nesting sites. Through sight and sound, Edwards documents which bird species are present in each of the sites she visits. 

Edwards will wrap up her work during the beginning of July. Her study will be used in combination with elk GPS collar data to determine what levels of elk activity have led to current aspen conditions. The information will also help predict how aspen stands may be affected if elk patterns change due to a shift in Refuge management activities. 

 

 

Last Updated: Jun 30, 2014
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