By Hayes Goosey and David Naugle
Land use such as livestock grazing — the most common use of rangelands — influence the abundance and composition of insects, which may have far-reaching effects on rangeland ecosystems. Grazing impacts arthropods through direct habitat disturbance as well as by changing the composition and physical structure of plant communities they rely upon.
That’s what a study comparing insect communities in grazed, rested, and idled pastures in Montana found. The types of insects that provide a critical food source for sage grouse chicks and other shrub- and grassland-dependent birds were 13% more prevalent on managed versus idled rangelands.
Studies show that grazing strategies that incorporate variation in grazing intensity, such as rest-rotation grazing that defers grazing certain pastures for a year or so, may be an effective tool for maintaining arthropod biodiversity on managed rangelands.
Research shows that 50% to 60% of the diet of 1- to 4-week-old sage grouse chicks is composed of insects such as beetles, ants, and caterpillars. Predatory spiders— which researchers found in abundance in idle, ungrazed pastures — eat the bugs that sage grouse need to survive and thrive.
About the research
Researchers from Montana State University investigated relative abundance and diversity of ground-dwelling arthropods in sagebrush habitats in central Montana from 2012–2015. The percentage of bare ground and the height of grass and sagebrush were also averaged for each location. Samples were collected weekly in three types of pastures:
- Deferred: Pastures in the “rest” phase of a rest-rotation grazing system, which involves moving livestock herds through multiple pastures during the season while leaving at least one pasture ungrazed for about 15 months to allow for plant growth and reproduction.
- Grazed: Pastures where livestock were present.
- Idle: Pastures where livestock grazing was absent for years.
Total insect catches were twice as high on idle pastures compared to managed pastures, and the totals trapped in grazed and deferred pastures did not differ. This corresponds to the reduced percentage of bare ground documented in sample areas on idled rangeland — increased grass and shrub cover likely support a higher abundance of arthropods.
But researchers discovered that the specific insect classes preferred by sage grouse were 13% more prevalent on managed pastures. Plus, managed rangeland supported a more diverse assemblage of ground-dwelling insects, which may be particularly beneficial for birds that rely on this critical food resource.
Grazing good for ecosystems and production
Well-managed livestock grazing of native plants is one of the best ways to benefit wildlife and working lands. Rangelands with lush native grasses, wildflowers, sagebrush, and wet meadows are the best habitat for arthropods, as well as sage grouse and hundreds of other species. Plus, managing for diverse, healthy plants put more pounds on livestock, too.
Goosey is a rangeland entomologist at Montana State University. Naugle is a wildlife biology professor at University of Montana.