Origin,Persistence, and Resolution of the Rotational Grazing Debate: Integrating Human Dimensions Into Rangeland Research

The debate regarding the benefits of rotational grazing has eluded resolution within the US rangeland profession for more than 60 yr. This forum examines the origin of the debate and the major reasons for its persistence in an attempt to identify common ground for resolution, and to search for meaningful lessons from this central chapter in the history of the US rangeland profession. Rotational grazing was a component of the institutional and scientific response to severe rangeland degradation at the turn of the 20th century, and it has since become the professional norm for grazing management. Managers have found that rotational grazing systems can work for diverse management purposes, but scientific experiments have demonstrated that they do not necessarily work for specific ecological purposes. These interpretations appear contradictory, but we contend that they can be reconciled by evaluation within the context of complex adaptive systems in which human variables such as goal setting, experiential knowledge, and decision making are given equal importance to biophysical variables. The scientific evidence refuting the ecological benefits of rotational grazing is robust, but also narrowly focused, because it derives from experiments that intentionally excluded these human variables. Consequently, the profession has attempted to answer a broad, complex question—whether or not managers should adopt rotational grazing—with necessarily narrow experimental research focused exclusively on ecological processes. The rotational grazing debate persists because the rangeland profession has not yet developed a management and research framework capable of incorporating both the social and biophysical components of complex adaptive systems. We recommend moving beyond the debate over whether or not rotational grazing works by focusing on adaptive management and the integration of experiential and experimental, as well as social and biophysical, knowledge to provide a more comprehensive framework for the management of rangeland systems.     

Adaptive,Multipaddock Rotational Grazing Management: A Ranch-Scale Assessment of Effects on Vegetation and Livestock Performance in Semiarid Rangeland

A comprehensive understanding of multipaddock, rotational grazing management on rangelands has been slow to develop, and the contribution of adaptive management (Briske et al. 2011) and sufficient scale (Teague and Barnes 2017) have been identified as key omissions. We designed an experiment to compare responses of vegetation and cattle in an adaptively managed, multipaddock, rotational system with that of a season-long, continuous system at scales comparable with those of a working ranch. We hypothesized that 1) year-long rest periods in the adaptively managed, rotational pastures would increase the density and productivity of perennial C₃ graminoids compared with continuously grazed pastures and 2) adaptive management, supported with detailed monitoring data, would result in similar cattle performance in the rotational as in the continuously grazed pastures. However, we found little supporting evidence for grazing management effects on C₃ graminoid abundance or production under either above-average or below-average precipitation conditions during the 5-yr experiment. Furthermore, adaptive rotational grazing resulted in a 12–16% reduction in total cattle weight gain relative to continuous grazing each year. Our work shows that the implementation of adaptive management by a stakeholder group provided with detailed vegetation and animal monitoring data was unable to fully mitigate the adverse consequences of high stock density on animal weight gain. Under adaptive rotational grazing, C₃ perennial grass productivity and stocking rate both increased following above-average precipitation. But when adaptive rotational management was directly compared with continuous grazing with the same increase in stocking rate, continuous grazing achieved similar vegetation outcomes with greater cattle weight gains. We suggest that managers in semiarid rangelands strive to maintain cattle at stock densities low enough to allow for maximal cattle growth rates, while still providing spatiotemporal variability in grazing distribution to enhance rangeland heterogeneity and long-term sustainability of forage production.     

青藏高寒草地夏秋季不同轮牧强度对牧草及绵羊的影响

本试验是在四川省阿坝州若尔盖县辖曼种羊场进行的。对种羊场的草地进行夏秋季轮牧强度试验，对轮牧小区内牧草产量、营养成份、绵羊生产性能进行测定，结果表明：从保护利用的观点着眼，草地轮牧强度应选择7．5只羊／ha，草地的可利用牧草为90％。日增重与日食量和放牧强度之间存在显著的多元线性回归关系，日增重与采食量呈正比，而与放牧强度呈反比。日采食蛋白与日增重比与日食量和放牧强度之间存在显著的多元线性回归关系，当放牧强度为3．75只羊／ha时日食蛋白与日增重比达到最低，为0．875，即绵羊对蛋白质的利用率最高。     

Grazing History Effects on Rangeland Biomass,Cover and Diversity Responses to Fire and Grazing Utilization

Exclusion of large grazers from rangelands that evolved with significant grazing pressure can alter natural processes and may have legacy effects by changing magnitude or direction of community responses to subsequent disturbance. Three moderately grazed pastures were paired with 12-ha areas with 15 yr of livestock exclusion. Six treatments were assigned to each in a 2 x 3 factorial arrangement of fire (fall fire or no fire) and grazing utilization (0%, 50%, or 75% biomass removal) to determine grazing history effects on rangeland response to subsequent disturbance. Livestock exclusion increased C₃ perennial grass (1 232 vs. 980 ± 50 kg ? ha^-1) and forbs (173 vs. 62 ± 19 kg ? ha^-1) and reduced C₄ perennial grass (36 vs. 180 ± 25 kg ? ha^-1) with no effect on total current-year biomass. Diversity was greater in pastures than exclosures (H’ = 1.5400 vs. 1.3823 ± 0.0431). Every biomass, cover, and diversity measure, except subshrub biomass, was affected by fire, grazing utilization, or both. Contrary to expectations, grazing history only interacted with fire effects for old standing dead material and interactions with grazing utilization were limited to old dead, bare ground, richness and dominance. Fire by grazing utilization interaction was limited to bare ground. Fire reduced annual grass (64 vs. 137 ± 29 kg ? ha^-1), forbs (84 vs. 133 ± 29 kg ? ha^-1), and diversity (H’ = 1.3260 vs. 1.5005 ± 0.0537) with no difference in total current-year biomass (1 557 vs. 1 594 ± 66 kg ? ha^-1). Grazing to 75% utilization reduced total current-year biomass (1 467 vs. 1 656 ± 66 kg ? ha^-1) and dominance (0.4824 vs. 0.5584 ± 0.0279). Grazing history affected starting points for most variables, but changes caused by grazing utilization or fire were similar between pastures and exclosures, indicating management decisions can be made based on independent knowledge of grazing or fire effects.     

Rangeland Livestock Production in Relation to Climate and Vegetation Trends in New Mexico

A large statewide historical database involving livestock numbers, vegetation cover, precipitation, air temperature, and drought frequency and severity allowed us to explore relationships between climate and rangeland livestock grazing levels and livestock productivity from 1920 to 2017. Trends in vegetation cover and livestock grazing levels from 1984 to 2017 were also explored. Our climate time series was divided into two periods, 1920 ? 1975 and 1976 ? 2017, based on an apparent accelerated increase in mean annual air temperatures that began in the mid-1970s. Both mean annual precipitation (MAP) and mean annual air temperature (MAT) differed (P ≤ 0.05) between the two periods. MAP and MAT were 9.6% and 3.4% higher in period 2 compared with period 1, respectively. From the 1920s to 2010s the livestock grazing level and weaned calf numbers fell 30% and 40%, respectively, despite a significant increase in MAP. Long-term declines in livestock grazing levels and in weaned calf numbers were significantly (P ≤ 0.05) correlated with increasing MAT (r = ? 0.34 and r = ? 0.43, respectively). No long-term trends (1984–2017) in woody or perennial herbaceous cover were detected at the level of the entire state of New Mexico. Woody plant cover dynamics for New Mexico were not related to livestock grazing levels. However, at the county level we detected a 2% increase in woody plant cover coupled with a 9% decrease in cattle animal units between 2000 and 2002 and 2015 and 2017 for 19 select counties well distributed across New Mexico. Increases in woody plant cover varied greatly among counties and were higher for eastern than western New Mexico. Both global and New Mexico data show the climate warming trend is accelerating. Our findings have relevance to several other parts of the world because New Mexico occurs at midlatitude, has varied topography and climatic conditions, and several different range vegetation types.     

不同放牧密度对草原植被特征的影响分析

呼伦贝尔天然草原在不同放牧半径条件下的草原植被演替特征，包括植被组成、群落主要植物的优势度、植被演替度、植被高度、盖度以及生产力与放牧强度的变化关系等。结果分析表明：呼伦贝尔草原放牧密度的差异将导致植被组成中的减少种、增加种与侵入种比例呈有规律改变，特别是随放牧密度的增大，侵入种比例急剧开始升高；同时草原植被中优势种比例下降，而且植被演替度减小，植被生产力下降。应用植被生态学的定量分析方法，对不同     

营养菌剂对枯草期和青草期绵羊的增重试验

用自制的营养菌剂在枯草期和青草期对青海省湖东种羊场的种羊和土种羊分别进行灌服试验，１５ｄ灌服１次，枯草期灌服８次，青草期灌服７次，每次每只羊５ｍｌ，结果表明，在枯草期，种羊试验组平均增重４．０３ｋｇ，对照组增重３．１４ｋｇ，土种羊试验组平均增重０．０１ｋｇ，对照组增重－１．２１ｋｇ；在青草期，种羊试验组平均增重４．１５ｋｇ，对照组增重３．４０ｋｇ，土种羊试验组平均增重１．７２ｋｇ，对照组增重１．３     

划区轮牧与草地可持续性利用的研究进展

划区轮牧是一种充分利用饲草生长旺季而进行的集约、区块式放牧管理系统。本文总结了近年来国内外轮牧制度的发展现状,概括了划区轮牧的优势包括:提高草地生态系统的功能性、草地生产力;降低草食动物肠胃线虫感染率;分析了其与传统连续放牧相比所具有的局限性。进一步从放牧类型的延展、放牧策略的改进、人为因素的投入、生态模型研究等多角度综合考究,提出综合协调生物因素与环境、平衡生态与经济以及优化牧企合作现状的轮牧策略,以期为轮牧对于生态恢复和草地可持续性利用的生产实践应用提供科学依据和优化管理的决策参考。     

浑善达克沙地草地放牧制度和特殊经营管理行为的研究

草地放牧制度不仅反映畜牧业生产的特征.也决定其性质.草地放牧制度选择的合理与否,直接影响草地资源的可持续利用和草地生态环境质量以及牧户经营收入.在阐述草原牧区草地放牧制度演变的基础上,采用基于随机抽样的人户调查和实地考察的方法,对位于浑善达克沙地的6个苏木290个牧户进行了调查研究,分析了牧户草地放牧制度的不同类型以及草地利用中的经营管理行为.     

Semiarid Rangeland Is Resilient to Summer Fire and Postfire Grazing Utilization

Most wildfires occur during summer in the northern hemisphere, the area burned annually is increasing, and fire effects during this season are least understood. Understanding plant response to grazing following summer fire is required to reduce ecological and financial risks associated with wildfire. Forty 0.75-ha plots were assigned to summer fire then 0, 17, 34 or 50% biomass removal by grazing the following growing season, or no fire and no grazing. Root, litter, and aboveground biomass were measured before fire, immediately after grazing, and 1 yr after grazing with the experiment repeated during 2 yr to evaluate weather effects. Fire years were followed by the second driest and fifth wettest springs in 70 yr. Biomass was more responsive to weather than fire and grazing, with a 452% increase from a dry to wet year and 31% reduction from a wet to average spring. Fire reduced litter 53% and had no first-year effect on productivity for any biomass component. Grazing after fire reduced postgrazing grass biomass along the prescribed utilization gradient. Fire and grazing had no effect on total aboveground productivity the year after grazing compared to nonburned, nongrazed sites (1 327 vs. 1 249 ± 65 kg · ha^-1). Fire and grazing increased grass productivity 16%, particularly for Pascopyrum smithii. The combined disturbances reduced forbs (51%), annual grasses (49%), and litter (46%). Results indicate grazing with up to 50% biomass removal the first growing season after summer fire was not detrimental to productivity of semiarid rangeland plant communities. Livestock exclusion the year after summer fire did not increase productivity or shift species composition compared to grazed sites. Reduction of previous years' standing dead material was the only indication that fire may temporarily reduce forage availability. The consistent responses among dry, wet, and near-average years suggest plant response is species-specific rather than climatically controlled.     

青海省三江源区天然草地改良与合理利用建议

阐述了青海省三江源区草地畜牧业与草地利用的现状和存在的问题。在分析其他地区草地利用经验的基础上,提出了该地区退化草地改良与合理利用的建议,供有关人员参考。     

Defoliation Intensity and Simulated Grazing Strategy Effects on Three C4 Rangeland Bunchgrasses

Defoliation intensity and timing are two important factors determining plants response to grazing. These factors can be managed by adjusting stocking rate and applying a grazing strategy. In a 6-yr clipping experiment conducted in northwestern Argentina, we assessed the effect of different defoliation intensities (~ 30%, ~ 50%, and ~ 70% removal of the annually produced aboveground biomass) and simulated grazing strategies (continuous grazing, two-paddock rest-rotation, three-paddock rest-rotation, dormant season grazing) on plots of three C4 native bunchgrasses (Pappophorum vaginatum, Trichloris crinita, and Digitaria californica). Response variables were mean and trend of clipped-off biomass during the 6 yr of treatments, number of inflorescences, and aboveground biomass produced on the year following treatments end (to evaluate residual effect of treatments). Results were species dependent. Mean clipped-off biomass increased with defoliation intensity in T. crinita and D. californica. However, defoliation intensity negatively affected clipped-off biomass trend in T. crinita and the production of P. vaginatum and T. crinita during “residual effect” evaluation. The three species responded positively at least in one response variable to the amount of rest periods in the grazing strategy. Our results are not fully consistent with the concept that forage production is more influenced by defoliation intensity than by grazing strategy: In two of the three species, grazing strategy presented greater impact on response variables than defoliation intensity. When significant “defoliation intensity × grazing strategy” was detected, intensity tended to be more detrimental as grazing strategy allows fewer rest periods. We observed a residual effect of treatments in the three species (generally, negative effect of defoliation intensity and positive effect of grazing strategies with more rest periods). Our results show that dormant season utilization and rest periods are beneficial for maximizing mean clipped-off biomass and ensuring clipped-off biomass trend. High defoliation intensities can maximize short-term clipped-off biomass, but it may produce negative residual effects and trends.     

Rotational Grazing on Rangelands: Reconciliation of Perception and Experimental Evidence

In spite of overwhelming experimental evidence to the contrary, rotational grazing continues to be promoted and implemented as the only viable grazing strategy. The goals of this synthesis are to 1) reevaluate the complexity, underlying assumptions, and ecological processes of grazed ecosystems, 2) summarize plant and animal production responses to rotational and continuous grazing, 3) characterize the prevailing perceptions influencing the assessment of rotational and continuous grazing, and 4) attempt to direct the profession toward a reconciliation of perceptions advocating support for rotational grazing systems with that of the experimental evidence. The ecological relationships of grazing systems have been reasonably well resolved, at the scales investigated, and a continuation of costly grazing experiments adhering to conventional research protocols will yield little additional information. Plant production was equal or greater in continuous compared to rotational grazing in 87% (20 of 23) of the experiments. Similarly, animal production per head and per area were equal or greater in continuous compared to rotational grazing in 92% (35 of 38) and 84% (27 of 32) of the experiments, respectively. These experimental data demonstrate that a set of potentially effective grazing strategies exist, none of which have unique properties that set one apart from the other in terms of ecological effectiveness. The performance of rangeland grazing strategies are similarly constrained by several ecological variables establishing that differences among them are dependent on the effectiveness of management models, rather than the occurrence of unique ecological phenomena. Continued advocacy for rotational grazing as a superior strategy of grazing on rangelands is founded on perception and anecdotal interpretations, rather than an objective assessment of the vast experimental evidence. We recommend that these evidence-based conclusions be explicitly incorporated into management and policy decisions addressing this predominant land use on rangelands.