ReviewMulti-paddock grazing on rangelands: Why the perceptual dichotomy between research results and rancher experience?
Introduction
Rangelands are diverse ecosystems and landforms that cover about half of the world's terrestrial area, excluding Antarctica and Greenland, and that are unsuited for intensive agriculture or forestry because of climatic, edaphic or topographic limitations (Holechek et al., 2004). People in many rural and urban populations depend on them for their livelihoods, often through livestock production, and for the ecosystem services that affect human well being. Such services include the maintenance of stable and productive soils, the delivery of clean water, the sustenance of plants, animals and other organisms that support human livelihoods, and other characteristics that support aesthetic and cultural values (Daily, 1997, Grice and Hodgkinson, 2002).
Healthy rangelands are more productive, stable and resilient than those in poorer condition and they provide greater earnings and more abundant ecosystem services (Heitschmidt and Taylor, 1991, Oesterheld et al., 1992, Milchunas and Lauenroth, 1993, Wessels et al., 2007, Teague et al., 2009a, Teague et al., 2011). Therefore, to support their sustainability, anyone who manages rangelands should aim to enhance the health and socio-ecological resilience of these ecosystems (Walker et al., 2002). This requires adopting long-term planning horizons, conserving primary resources, choosing appropriate management goals, and continually adapting to dynamic ecological, social, and economic conditions.
Changes in environmental conditions often happen so gradually that most people are unaware of them until some threshold condition has been exceeded (Senge, 1994). Unless sufficiently sensitive indicators of change are continually monitored, landowners who focus on short-term profit maximization may not realize that the ecosystems upon which their production systems depend are being systematically degraded (Kothmann et al., 1971, Whitson et al., 1982, Knight et al., 1990, Teague et al., 2009a). As a result, maximizing livestock production from rangelands is inevitably an unsustainable goal both ecologically and economically (Workman, 1986). To remain economically viable, managers must maintain or improve the biophysical functions and processes necessary for sustaining ecosystem health and resilience, including soil organic matter accumulation, solar energy capture, water infiltration, and nutrient cycling while also maintaining ecosystem biodiversity. In the long term, this strategy provides the greatest cumulative production potential and economic profits without decreasing delivery of ecosystem services for society.
Ranchers with secure land tenure generally have a vested interest in managing their resources for sustained high yields and profitability. Achieving this goal requires ranchers to integrate knowledge from biological, economic and management disciplines and to continually adjust management actions in response to changing environmental and socio-economic conditions. In response, people have developed numerous grazing strategies for sustaining and improving rangeland health. However, applying any of them successfully requires the use of adaptive management based on relevant scientific information and, equally importantly, local knowledge and experience to respond to ever-changing circumstances (Walters, 1986, Holling and Meffe, 1996, Walker et al., 2002). The benefits of multi-paddock grazing for maintaining productivity and profitability and for adaptive management responses to changing conditions have been evident to ranchers for many years in many countries (Tainton et al., 1999, Teague et al., 2009b). However, recent reviews of published rangeland grazing studies suggest that multi-paddock rotational grazing improves neither vegetation nor animal production relative to single-paddock continuous stocking (Briske et al., 2008).
The goal of our paper is to provide a framework for rangeland management decisions to enhance ecosystem resilience and delivery of ecosystem services and to develop testable hypotheses that explain the differences in perspectives of ranchers' observations and scientific research results. In presenting the framework and hypotheses, we distinguish between principles and processes of adaptation and their local manifestations for plants, herbivores, and people. Many publications report the manifestations of particular responses unique to local conditions for plants, herbivores and researchers, and do not focus on principles and processes, which are required to increase broader understanding of responses to management actions. While principles and processes apply generally across time and space, the application of treatments varies from time-to-time and place-to-place, which makes their responses unique in space and time.
The reason for developing and implementing grazing management strategies as alternatives to continuous grazing is to prevent the degradation of rangeland ecosystems and to enhance ecological functions that increase primary and secondary production, and to provide other ecosystem services. Short-term field studies of grazing management have generally incorporated a minimal number of grazing system variables, notably plant and animal production, to obtain publishable results. In most cases, they have not investigated grazing management impacts on other system elements nor the interaction of these components. In addition, the spatial and temporal scales of such research are generally smaller and shorter, respectively, than those faced by ranchers. Therefore, the results of these grazing systems studies must be interpreted carefully to determine their value and applicability at a ranch-operation scale. When applied rigidly at these larger scales, they have often led to different and unsatisfactory outcomes. Accordingly, we concentrate our inquiry on determining the management principles, processes and approaches needed to maintain or improve the ecological function and biological resources upon which productivity is based, rather than on examining what management results in the highest productivity without examining long-term consequences on ecosystem function (see Van der Ploeg et al., 2006 for a discussion of these ideas regarding a grassland experiment).
The manuscript is based on five focal areas of inquiry. First, we outline the ecology of grazed ecosystems under free-ranging and single-paddock herbivory conditions. Second, we identify five principles underpinning the actions used by successful grazing managers and the ecological, physiological, and behavioral framework they use to achieve desired conservation, production, and financial goals. Third, we examine the adaptive management principles needed for sustainability in variable environments. While understanding ecological processes is critically important, such knowledge is insufficient for sustainable outcomes; to respond to ever-changing ecological, social, and economic conditions, people must combine knowledge of plant and animal ecology, physiology, and behavior with adaptive, goal-oriented decision-making. Fourth, we describe differences between the interpretation of results of grazing systems research reported in the scientific literature and the knowledge gained by successful grazing managers. In association with this we outline the shortcomings of grazing system research for providing information relevant for rangeland managers to meet their desired environmental and economic goals. Finally, we outline knowledge gaps and associated research needed to provide a clearer understanding of how grazing management can achieve desired socio-ecological goals. To facilitate future research, we develop testable hypotheses to explain why recent reviews of research have arrived at conclusions that differ from those obtained by many successful conservation award-winning ranchers. Given that the scientific procedure involves formulating testable hypotheses that aim to explain observations (Popper, 1959, Kuhn, 1970), we present well-founded observations from numerous sources to formulate testable hypotheses.
Section snippets
Grazing effects under free-ranging herbivory
From the late Mesozoic Era, grazing by large ungulates has been an integral part of most ecosystems. The co-evolution of plants and herbivores under changing environmental conditions has resulted in highly resilient grazed ecosystems that support more animal biomass and sustain considerably higher levels of herbivory than other terrestrial habitats (Stuart Hill and Mentis, 1982, Frank et al., 1998). Grazing, fire and fluctuating climatic regimes create the dynamic resilience of organisms that
Principles of successful grazing management
Ranching in rangeland ecosystems is characterized by ever-changing and unpredictable environmental conditions and circumstances due to low, variable and spatially and temporally heterogeneous precipitation and plant productivity, and to fluctuating economic conditions driven by market price fluctuations and shifting social values. Successful rangeland managers enhance the health of the ecosystems upon which they depend, their profitability and their life quality, while also providing ecosystems
Adaptive management in variable environments
Management is relatively easy when resources for plant growth are abundant and predictable and when forage quality is reasonably high and consistent. Rangelands, by contrast, are difficult to manage because decisions must accommodate substantial change and uncertainty including inter- and intra-seasonal climatic variations with periodic droughts, low and variable forage quality, and variation in social preferences and economic factors that affect profitability (Tainton et al., 1999; Sayre, 2001
Limitations of experimental evidence
To be scientifically sound and meaningful for managers, a primary goal of any grazing experiment and the execution of any grazing treatment should be to enhance soil, vegetation, animal, and human performance over many years. Without this emphasis, and if the experimental design and implementation favors one outcome, it is inaccurate to claim that a given grazing treatment produced no better or inferior results than another treatment. When researchers conduct grazing trials, they become
New theories and testable hypotheses
Although many disciplines have historically operated on the tenets of a single major paradigm, considering and comparing more than one paradigm often generates more complete knowledge than is possible with only one (Burrell and Morgan, 1979, Frost, 1980, Provenza, 2000). Different paradigms are based on fundamentally different assumptions and produce markedly different ways of approaching and building a theoretical foundation for any discipline (Gioia and Pitre, 1990). Moreover, according to
Conclusions and recommendations
The benefits of effective multi-paddock grazing management, as well as the results of poor grazing management, have been observed and reported for many years and in many countries. Ironically, despite the observed and reported benefit to species composition and vegetation cover with planned grazing and adequate recovery, recent reviews of rangeland grazing studies suggest that multi-paddock grazing improves neither vegetation nor animal production relative to continuous stocking (Briske et al.,
Acknowledgments
The authors gratefully acknowledge the funding provided by the Texas A&M AgriLife Research under project H 8179. Some of the ideas presented in this manuscript were previously published in: Benefits of Multi-Paddock Grazing Management on Rangelands: Limitations of Experimental Grazing Research and Knowledge Gaps. In: Grasslands: Ecology, Management and Restoration, Editor: Hans G. Schroder, pp. 41–80. Nova Science Publishers, Inc. ISBN 978-1-60692-023-7. They are included with permission from
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