Landscape Changes in Browse Condition by Wild and Domestic Ungulates

The level of browsing by wild and domestic ungulates is an important influence on the structural diversity and species composition of plant communities. Under low browsing pressure, young plants attain their potential stature and contribute to the structural diversity of the community by replacing older plants as they die. The resulting vegetation structure and species composition produces habitat that is of value to a variety of wildlife, including breeding birds. If browsing pressure increases to a level that prevents young plants from growing through the browse zone, structural diversity will decrease and species composition will be altered. The resulting habitat becomes less suitable for the original suite of wildlife, including the wild ungulates that contributed to the altered state. Over the past several decades, many parts of Montana have experienced an increase in the population of wild ungulates. While mule deer populations have declined from peak levels, elk populations have increased. As a result of these population changes, herbivory has increased at some locations to levels that prevent young plants from growing through the browse zone. At these locations, the vegetation community consists of plants that attained full stature when browsing pressure was low, and short, heavily-browsed younger plants. As the older plants die over a period of decades, structural diversity diminishes.

Fire accelerates the loss of structural diversity by removing the mature plants before they die of old age. Without the mechanical protection of the older plants, all plants are accessible to ungulates. The recent increase in fire frequency in combination with the increase in ungulate population size places large areas of habitat at risk. To effectively manage for sustainable habitat requires the ability to detect declines in structural diversity at an early stage.

Current Projects

• Develop Methods of Detecting Declines in Structural Diversity
• Conduct Case Study of Post-fire Effect on Skunkbush and Chokecherry in Eastern Montana
• Conduct Case Study to Explore Potential for Documenting the Effect of Herbivory on Big Sagebrush

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