Livestock grazing on public lands has become one of the most contentious issues in the southwestern United States during the 1990s. On one side of the debate are environmentalist activists that perceive the impact of livestock on native, intact ecological communities as extreme and unacceptable. On the other side of the debate are traditional ranchers, many of whom are long-time residents contending that the overall condition of rangelands has improved in their lifetimes. Somewhere in the middle are an increasing number of ranchers and land managers who argue that while traditional grazing practices can result in rangeland degradation, grasslands can actually be improved through the use of high-intensity, short duration grazing rotation strategies.
Is there a role for science amidst this debate? We believe
that the answer is yes, and that scientists can help to clarify
the biological resource issues at stake and, once clarified,
design experiments involving the ideas and participation of different
constituencies in the debate. The discussion of livestock grazing
on arid lands is often muddled by the use of ill-defined terms
such as "ecosystem health" or "rangeland condition."
We believe that the discussion can be clarified and moved forward
if such general terms are replaced by two distinct, measurable
ecosystem characteristics: biological diversity and ecosystem
productivity. We have initiated a research project that will
examine how plant and arthropod diversity and net primary productivity
of arid grasslands vary as functions of livestock grazing intensity.
The four treatments include: 1) livestock exclosure, 2) traditional
low-intensity, long-duration grazing rotation, 3) high density,
short-duration, HRM-style grazing and 4) extremely high density,
short-duration grazing (to simulate herd-impact).
In central Arizona we established one long-term study site in 1997 and another in the fall of 1998. Both sites are comprised of replicated, 1-ha plots on grasslands managed under the 4 different management treatments listed above. Blocks of these four treatments are replicated three times at the study sites. Unlike most other studies that have compared the effects of different stocking densities on soils and vegetation, this study stresses practical implications by working on operating ranches. Ranchers are responsible for deciding animal stocking densities and grazing durations while researchers examine changes in plant and arthropod diversity, net primary productivity as well as factors that underlie diversity and/or productivity, such as soil moisture dynamics, associative nitrogen fixation, standing biomass, decomposition, and cycling of nitrogen and phosphorus.
Our research program has developed a strong educational component involving graduate and undergraduate students at two institutions, as well as ranchers, environmentalists, and other interested citizens. A fundamental objective of this study is to bridge the existing gulf between research science, ranchers and other land managers, and the public.