Abstract
Livestock grazing can be used as a key management tool for maintaining healthy ecosystems. However, the effectiveness of using grazing to modify habitat for species of conservation concern depends on how the grazing regime is implemented. Timing of grazing is one grazing regime component that is less understood than grazing intensity and grazer identity, but is predicted to have important implications for plant and higher trophic level responses. We experimentally assessed how timing of cattle grazing affected plant and arthropod communities in high-elevation grasslands of southwest Montana to better evaluate its use as a tool for multi-trophic level management. We manipulated timing of grazing, with one grazing treatment beginning in mid-June and the other in mid-July, in two experiments conducted in different grassland habitat types (i.e., wet meadow and upland) in 2011 and 2012. In the upland grassland experiment, we found that both early and late grazing treatments reduced forb biomass, whereas graminoid biomass was only reduced with late grazing. Grazing earlier in the growing season versus later did not result in greater recovery of graminoid or forb biomass as expected. In addition, the density of the most ubiquitous grassland arthropod order (Hemiptera) was reduced by both grazing treatments in upland grasslands. A comparison of end-of-season plant responses to grazing in upland versus wet meadow grasslands revealed that grazing reduced graminoid biomass in the wet meadow and forb biomass in the upland, irrespective of timing of grazing. Both grazing treatments also reduced end-of-season total arthropod and Hemiptera densities and Hemiptera biomass in both grassland habitat types. Our results indicate that both early and late season herbivory affect many plant and arthropod characteristics in a similar manner, but grazing earlier may negatively impact species of conservation concern requiring forage earlier in the growing season.
Highlights
Grazing is a key process in grasslands that has far reaching effects on plant and animal diversity [1,2,3], vegetation structure [4], and ecosystem functioning [5] over multiple spatial scales
Our grazing experiment in high-elevation, western U.S grasslands demonstrated that grazing altered plant and arthropod characteristics within a single growing season. We found that both timing of grazing treatments generally reduced plant biomass and height, and grazing earlier versus later in the growing season did not result in greater recovery for graminoid or forb biomass
Our results suggest that the influence of grazers on plant communities may depend on both grassland habitat type and plant functional group, but climatic variation is likely to influence grazing outcomes
Summary
Grazing is a key process in grasslands that has far reaching effects on plant and animal diversity [1,2,3], vegetation structure [4], and ecosystem functioning [5] over multiple spatial scales. Native ungulate grazers dominated certain landscapes prior to European settlement, many of these grasslands around the world are grazed by domestic livestock [6]. In 2007, approximately 27% of U.S land area was classified as grassland pasture and range for livestock production [7]. Current grazing management strategies aim to balance both ecological sustainability and economic considerations [8]. Most conservation practitioners recognize that grazing may be used as an important land management tool [9,2]. Grazing can be used to modify habitat for species conservation, as demonstrated through improvements of grassland bird habitat [10,11]
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