PREDICTABILITY OF EFFECTS OF ROTATIONAL GRAZING SYSTEMS ALONG ENVIRONMENTAL GRADIENTS

Authors: Derner, Justin; Gillen, Robert

Submitted to: Society for Range Management Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 9/1/2005
Publication Date: 2/11/2006
Citation: Derner, J.D., Gillen, R.L. 2006. Predictability of effects of rotational grazing systems along environmental gradients. Society for Range Management Meeting Abstracts. CD-ROM Rangeland to Rainforests #87.

Interpretive Summary:

Technical Abstract: Rotational grazing systems have been implemented in numerous rangeland ecosystems with the desired objectives of increasing homogeneity of use of vegetation through high stocking densities within small pastures and increasing stocking rate. Vegetation and livestock responses to rotational grazing, with rare exceptions, are similar to continuous, season-long grazing in native rangeland ecosystems receiving <1000 mm annual precipitation. This is attributable to belowground constraints (e.g., soil water) determining plant-soil relationships in these systems as rotational grazing does not directly modify belowground parameters. In contrast, forage agro-ecosystems in high precipitation environments (>1000 mm), which are characterized by aboveground constraints (e.g., light) being the drivers of plant-soil relationships, benefit from rotational grazing as leaf area can be optimized and forage quality maintained by reducing the proportion of plants in a reproductive state. Thus, effects of rotational grazing are predictable along environmental gradients with benefits of this management practice in simple, low-diversity forage agro-ecosystems where high stocking densities on very small land areas reduce light competition, but no advantages are realized in native rangeland ecosystems where strong water limitation and high relative allocation of resources belowground are largely unaffected by rotational grazing. Because rangeland ecosystems are comprised of heterogeneous assemblages of plant communities, each distinguished by relative proportions of plants differing in photosynthetic pathway, physiognomy, growth form, and spatial and temporal distributions, we suggest that the paradigm of rotational grazing in these systems be changed. Rather than attempt to use rotational grazing to achieve the objective of increasing homogeneity of use of vegetation, we envision that land managers use rotational grazing to manipulate seasonality of grazing and utilization levels within individual pastures to achieve a suite of resulting plant communities that, although homogeneous at the pasture level, collectively achieve the desired objective of vegetation that is heterogeneous in structure and composition at ranch-to-landscape scales.