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Copyright © 2002 by the author(s). Published here under license by The Resilience Alliance.

The following is the established format for referencing this article:
Fehmi, J. 2002. The context of grassland defoliation. Conservation Ecology 6(1): r7. [online] URL: http://www.consecol.org/vol6/iss1/resp7/


Response to Gutman et al. 2002. "Biomass partitioning following defoliation of annual and perennial Mediterranean grasses"

The Context of Grassland Defoliation

Jeffrey Fehmi


ERDC-CERL Ecological Processes Branch

Published: April 1, 2002


The underlying assumption of Gutman et al. (2002) seems to be that livestock management is the determinant of vegetation structure. With stocking rates typical of the developed world, which may use even less than half of the available forage, this may not be true. Experimental treatments in this study (as well as in most other field-based livestock studies) may have inadvertently combined the direct impact of livestock with an indirect response of voles or other rodents. In the control or lesser-grazed treatments in livestock grazing studies, the increased biomass and vegetation cover greatly enrich rodent habitat and often allow populations to increase (especially voles). The disproportionately high metabolic rates, activity levels, and corresponding appetites of such rodents have the potential to profoundly impact these systems. In addition to the food consumed, other behaviors, such as the aboveground runways (tunnels made from clipped vegetation) constructed by many species of voles, can also destroy substantial amounts of vegetation.

The interacting effects of cattle and voles might explain the inconsistent results from grazing experiments and their derived management practices, including seasonal grazing practices designed to maintain and enhance native perennial grasses. It seems easy to conclude that grazing studies that control only livestock may not answer important questions about the forces that structure plant communities or control the responses of individual species. For instance, one recent study demonstrated that the impact of six months of vole activity was still apparent nearly 3 yr after voles were excluded from the study area (Howe and Brown 2001). Future livestock impact studies need to better document the relationship between the plant community and rodent activity, especially with experiments that directly manipulate rodent numbers.


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LITERATURE CITED

Gutman, M., I. Noy-Meir, D. Pluda, N. A. Seligman, S. Rothman, and M. Sternberg. 2002. Biomass partitioning following defoliation of annual and perennial Mediterranean grasses. Conservation Ecology 5(2): 1. [online] URL: http://www.consecol.org/Journal/vol5/iss2/art1

Howe, H. F., and J. S. Brown. 2001. The ghost of granivory past. Ecology Letters 4:371-378.


Address of Correspondent:
Jeffrey Fehmi
U.S. Army Corps of Engineers
Engineer Research and Development Center
Construction Engineering Research Laboratory
Ecological Processes Branch
2902 Newmark Drive
Champaign, Illinois 61822 USA
Phone: (217) 352-6511 Ext.: 6366
jeffrey.s.fehmi@erdc.usace.army.mil



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