Community responses of arthropods to a range of traditional and manipulated grazing in shortgrass steppe

Authors: NEWBOLD, SCOTT - COLORADO STATE UNIVERSITY; STAPP, PAUL - CAL-STATE FULLERTON; LEVANSAILOR, KATHERINE - CAL-STATE FULLERTON; Derner, Justin; LAUENROTH, WILLIAM - COLORADO STATE UNIVERSITY

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/10/2014
Publication Date: 5/29/2014
Citation: Newbold, S.T., Stapp, P., Levansailor, K.E., Derner, J.D., Lauenroth, W.K. 2014. Community responses of arthropods to a range of traditional and manipulated grazing in shortgrass steppe. Environmental Entomology. 43(3):556-568.

Interpretive Summary: Effects of experimental treatments involving grazing in the shortgrass steppe rangeland ecosystem have emphasized livestock gains and plant community changes, with responses of consumer groups (arthropods (e.g. insects, spiders) and small mammals) largely unknown. Here we used a gradient of livestock grazing including no grazing (long-term excluded from grazing since 1939), traditional season-long (May-October) grazing at the recommended stocking rate without areas colonized by prairie dogs, very heavy grazing with double stocking rates in the spring or summer, and grazing at the recommended stocking rate with areas colonized by prairie dogs. Grazing influenced vegetation structure (height) but not arthropod communities, and small mammal communities only differed between the no grazing and grazing plus prairie dog treatments. Consumer responses may lag behind responses of plants in this ecosystem, and these results suggest that grazing can be an important tool in the toolbox for land manager to balance production and conservation goals.

Technical Abstract: Livestock grazing has context-dependent impacts on grassland plant and animal communities. In grassland ecosystems that have evolved with large herbivores, such as the North American Great Plains with bison (Bison bison), responses of plants to grazing are better understood, and more predictable, than responses of consumers. In 2003, we began a large-scale, replicated experiment to examine effects of a grazing gradient on communities of two important consumer groups, arthropods and small mammals, in shortgrass steppe of northeastern Colorado, USA. Our objectives were: 1) to assess whether modifications of the intensity and seasonality of livestock grazing alter structure and diversity of arthropod and small mammal communities compared to traditional grazing regimes; and 2) to determine whether responses by these consumer groups are similar, and therefore provide broader generalizations of consumer responses. Treatments consisted of long-term grazing exclosures, moderate summer grazing (traditional), very intensive spring and summer grazing, and moderately grazed pastures that were also colonized by prairie dogs (Cynomys ludovicianus). In 2004 and 2006, attributes of vegetation structure and arthropod and small mammal communities were sampled on each study plot (n = 4--6 0.81-ha plots per treatment; 25 total plots). Grazing treatments affected vegetation structure, and treatments representing the extremes of the grazing gradient (long-term exclosures and grazed prairie dog colonies) affected small mammal, but not arthropod, consumer communities. Our findings suggest that responses of consumers to grazing may lag behind those for plants in this ecosystem. These results indicate that grazing is a useful tool for balancing production and conservation issues in the shortgrass steppe where services can be provided to society with only marginal impacts on community responses of consumers.