The systems approach to ecological research

Although it has become standard practice in Southern Africa to recommend grazing systems based on a maximum of five camps, there are indications that the use of multicamp layouts, employing a greater number of camps per herd, may increase the efficiency of animal production from natural veld. The basic advantage of multicamp layouts appears to lie in the inherent flexibility of the management which may be applied within such layouts, allowing the grazier to apply management as dictated by variable rainfall and according to the specific requirements of each camp.

Although multicamp layouts cannot be finally evaluated at this early stage, practical cases in a variety of veld types indicate that this approach is neither too expensive nor too complicated for commercial use.     

A comparison of grass and grass/legume pastures under irrigation in the Outeniqua area of the southern Cape

Two grass and five grass/legume pastures were evaluated over a period of two seasons at two seasonally set grazing pressures and under two grazing management systems, involving five and seven paddocks per flock and a seven‐day period of stay. Grazing capacity was most limiting during winter. Pastures with fescue as grass component had, overall, the highest grazing capacity, while white clover‐based pastures had the highest animal production. The legume content of the grass/legume pastures was markedly higher on the seven than on the five‐paddock system. Dry matter and animal production of white clover‐based pastures was favoured by a seven‐paddock system as opposed to a five‐paddock system, while mixtures containing lucerne and pure grass pastures were either not influenced by grazing management or promoted by a five‐camp system.     

2. Veld reinforcement for increased meat production

A programme of radical veld improvement applied on a farm in a cool, high rainfall area of East Griqualand is described. The veld was burnt in spring and fertilized with 300 kg/ha superphosphate and 45 to 60 kg/ha N. It was then heavily grazed with cattle and sheep during summer, using an eight‐camp rotational system, and in February it was oversown with cocksfoot and given a further 45 kg/N/ha. Grazing, with cattle only, continued into autumn. In the second year clover was sod‐seeded into part of the area.

With the eight‐camp grazing system, the number of MLU grazing days per ha increased from 161 on unimproved veld to 411 in the third year after improvement. In addition, the conception rate of cows increased from 85% to 97% and lambs could be run on the area which previously would support only mature, dry sheep.     

An analysis of the fundamentals of grazing management systems

The resting and grazing components of grazing management cycles as practised in South Africa are evaluated from the points of view of objective and effect. While the desirability of resting for seeding and an increase in vigour is recognized, little is known of the optimum duration and frequency of rests in the various types of grazing. The upper limit of camp numbers per group of animals beyond which an increase in resting benefit is only slight appears to be approximately six. While continuous grazing is generally believed to be detrimental to sward composition because of selective grazing, it seems that this effect is due rather to incorrect stocking rates than continuous grazing per se. Rotational grazing does, however, offer a means of attaining higher stocking rates without detrimental effects. High Utilization Grazing and High Production Grazing are two different methods of applying rotational grazing which have different objectives and different effects. The most suitable method to use in any situation depends on the nature of the sward and the reaction of the component species to defoliation. However, both methods require multi‐camp systems for best results.     

A physiological approach to research in pasture utilization

A study of species selection by cattle under a system of controlled selective grazing using wheel‐point surveys and fistulated animals has demonstrated that both techniques provide valuable information on the preference shown for such species as Andropogon amplectens, Eulalia villosa, Themeda triandra, Trachypogon spicatus, Tristachya hispida and Monocymbium ceresiiforme.

The wheel‐point survey, which presents information on the degree of utilization of different species over the entire grazing period, is complemented by the more detailed information obtained by identifying grass species from oesophageal fistula samples obtained at specific times within the grazing period.

Preference for species does not appear to be markedly affected by their relative contribution to basal cover, but apparently is subject to seasonal variations.     

Recent trends in grazing management philosophy in South Africa

Abstract

Reasoned argument by researchers in veld management in South Africa and elsewhere has not generally supported a number of contentious recommendations made in recent years in the popular and semi‐popular press. The only major changes to general management thinking has been that high performance grazing (or controlled selective grazing) is, except for a few notable exceptions, more appropriate than high utilisation grazing (non selective grazing). In contrast, considerably more evidence has emerged to support the general philosophy which has built up over the years on such issues as optimum stocking rates, periods of absence, stocking densities and the required number of camps in grazing layouts.     

The effect of veld condition on the quality of diet selected by cattle grazing the Natal Sour Sandveld

The quality of diet selected by steers fistulated at the oesophagous was related to veld condition in a simulated rotational grazing system on the Natal Sour Sandveld. Six camps, ranging in veld condition score from 8,5 to 53%, were grazed simultaneously for a two‐week period in spring, summer, autumn and winter. Fistula samples were collected on the first, middle and last day of a period of occupation in a camp. Samples were analysed in terms of crude protein (CP), in vitro digestibility (IVD) and plant‐part (% leaf, % stem and % dead material) composition. Dietary quality in terms of CP, IVD and plant‐part composition was not related to veld condition but was dependent largely (P≤0,01) upon season and to a lesser extent upon period of occupation in a camp. It was concluded that in sourveld areas, where dietary quality may be limiting, the veld condition score may be a poor index of potential animal production.     

Recent progress in the study of behavior and management in grazing cattle

Recent progress in studies concerning behavior of, and management for, grazing cattle are reviewed. Since 1950, much study has been conducted on ‘How’, ‘When’, ‘Where’ and ‘How long’ regarding grazing. After the 1980s, grazing ecology introduced the concept of hierarchy at different spatial and temporal scales, and since then grazing behavior has been investigated on the foraging hierarchy of large grazing herbivores: bite, feeding station (FS), patch, feeding site, camp and home range. From the sequence of activities, FS is grouped within a feeding patch, and movement of grazing cattle has been studied between FSs, feeding patches, feeding sites and between camps. Grazing behavior and production relates closley with defoliation, and grazing management should control both grazing behavior and vegetation according to three rules: planning, operational and adaptation rules. Planning rules relate the stocking rate of cattle; operational rules relate to defoliation; and adaptation rules vary with regional situations. Recent studies on grazing have been carried out in the fields of animal diversity and welfare. Future studies in this field should be conducted on the ecology, neurophysiology and psychology of grazing. Nonlinear analysis will also be significant in this field. Grazing cattle production should also utilize supplementation by roughage and/or grains.     

Development of veld management research in the karoo region

The development of veld research in the semi‐arid Karoo areas since 1934 is outlined. It entailed key experiments on different types of veld, and the synthesis of grazing systems and their testing in experimental camps and co‐operatively on a practical farming scale. The experiments were primarily conducted with Merino sheep but Angora goats, Boer goats, cattle and Persian sheep were also employed. A large number of rotational grazing systems, special treatments and methods have been set out for the entire Karoo Region. The group camp approach serves as a basis for complete veld management planning in the Karoo Region.

Supporting research covered plant physiological, phenological and ecological studies; the determination of selective grazing habits of livestock; production of karoo bushes; and the development of research techniques especially in connection with quantitative and qualitative vegetation surveys.     

Twice-Over Rotational Grazing and Its Impacts on Grassland Songbird Abundance and Habitat Structure

The majority of native prairie has been lost throughout North America. Much of the remaining prairie is used for livestock grazing, so conservation of prairie species depends on sustainable grazing practices. Our objective was to evaluate the benefits of twice-over rotational grazing, in comparison with continuous season-long grazing and ungrazed “idle” fields, in conserving prairie songbirds. Northern mixed-grass prairie in southwest Manitoba, Canada is near the northern range limits for many endangered grassland birds, and thus is an important area for evaluating the contribution of twice-over grazing in the conservation of songbirds, including species at risk. In 2008 and 2009, we compared the relative abundances and diversity of grassland birds on 22 twice-over rotation, 15 season-long, and 8 ungrazed sites, using multiple 100-m fixed-radius point-count plots per site. Analyses were conducted using generalized linear mixed models. Although one obligate grassland bird, Savannah sparrows (Passerculus sandwichensis), had significantly higher relative abundances on twice-over than season-long sites in 2009, season-long pastures had higher species richness and diversity of obligate grassland birds in both years. Season-long grazing may actually benefit grassland bird communities by creating spatially heterogeneous but temporally stable areas of high and low livestock use within the pasture, thus increasing diversity of microhabitats. We found little evidence that twice-over grazing contributed to the conservation of grassland songbirds in subhumid northern mixed-grass prairies.     

Are Droppings,Distance From Pastoralist Camps,and Pika Burrows Good Proxies for Local Grazing Pressure?

Grazing is regarded as one of the most important factors influencing rangeland ecosystems. Many previous studies have used indirect measures (proxies) of grazing intensity, such as the distance from congregation areas and the number of herbivore excreta, to estimate effects of grazing on vegetation parameters in rangeland ecosystems. However, little is known about how such proxies reflect the true grazing intensity, and if their suitability is consistent across landscape conditions. We measured grazing intensity based on the amount of plant ramets being grazed in 75 plots positioned across a rangeland landscape in central Tibet. Several grazing intensity proxies (distance from pastoral camp sites, number of yak dung patches (old and fresh), sheep and goat dropping piles, and pika (Ochotona curzoniae) burrows (active and abandoned)) were also measured in each plot. Regression models were used to examine the suitability of these proxies in predicting our measure of real grazing intensity. None of the examined proxies satisfactorily predicted real grazing intensity in our study system. The distance from camp sites was the best proxy for grazing intensity (P<0.001), but it explained only 30% of its variation. Fresh yak dung and active pika burrows explained only 10% and 3% of the variation in grazing intensity, respectively. The suitability of using proxies for grazing intensity did not significantly differ along landscape parameters (elevation, aspect directions, and slope angle) (P>0.05), except that the number of animal excreta and pika burrows functioned better as proxies at low, compared to high, elevation (P<0.05). Our results should be of concern since many studies use proxies to estimate effects of grazing on vegetation dynamics and ecosystem properties. We recommend awareness of potential limitations and suitability of proxies, when real grazing intensity is not measured.     

放牧强度对羊草草地植被特征的影响

通过小区控制放牧实验，研究了放牧强度对松嫩平原羊草草地植被特征的影响。结果表明：主要种群的高度、密度和生物量随季节的变化趋势不同，草地高度随放牧强度的增大而降低；一定程度的放牧可增加禾草在群落中的比例，提高牧草质量；随着放牧强度的增大，群落密度有增大的趋势，植物多样性指数先增高后降低，即中度放牧下多样性指数最大，有利于多样性的维持，多样性增加又增强草地对放牧的缓冲力。植物种数与多样性指数间没有明显的线性关系。     

马鹿夏季放牧对祁连山草原群落多样性的影响

祁连山草原是我国重要的生态安全屏障,素有“高原冰原水库”和“生命之源”之称,同时也是我国西北地区“江河源”、河西走廊水资源安全的战略基地。祁连山北坡高寒灌丛作为这个安全屏障的重要组成部分,对区域内畜牧业发展的贡献不可忽视。马鹿是祁连山草原重要的特色放牧家畜,目前关于马鹿放牧对高寒灌丛群落学过程的影响研究缺乏。本研究在祁连山中段北麓以甘肃马鹿-高寒灌丛放牧系统为研究对象,探讨了夏季马鹿的放牧强度和地形对高寒灌丛β和γ多样性的影响。结果表明:1) 阴坡和谷地放牧强度之间β多样性差异显著,谷地β多样性嵌套现象显著;2) 中度放牧促进γ多样性,地形间差异不显著。总体来讲,马鹿适度放牧显著提高了高寒灌丛草地的γ多样性。研究结果以期为祁连山草原的可持续放牧管理提供科学理论依据。     

放牧强度对高寒混播人工草地群落特征及地上现存量的影响

为探讨高寒牧区牧草生长季放牧强度对多年生混播人工草地群落特征及地上现存量的影响,从2003年至2005年在垂穗披碱草(Elymus natans)/星星草(Puccinellia tenuflora)混播草地上开展了牦牛放牧控制试验。结果表明:植被盖度随放牧强度的增加而降低,放牧强度对放牧区植物群落盖度的影响极显著(P<0.01);放牧强度与物种丰富度S、多样性指数H′、多样性指数D(除了第1年)和均匀度指数J′(除了第2年)均呈显著或极显著的二次回归,各放牧区与对照区植物群落的相似性系数与放牧强度成显著负相关(R=-0.9205),说明各放牧区植物群落朝着远离对照群落的方向演替;放牧强度和放牧时间对地上生物量的影响极显著(P<0.01),且随着放牧强度的增加,各处理组同一时期地上生物量逐渐减小。     

藏北高寒草地土壤真菌群落系统发育多样性对放牧的响应

本研究依托沿海拔梯度布设的三个配对的围栏和自由放牧样地探讨了土壤真菌系统发育多样性对放牧的响应规律.结果表明:暖季放牧和冷季放牧都没有改变高寒草原化草甸土壤真菌系统发育α多样性,暖季放牧也没有改变高寒草甸土壤真菌系统发育α多样性;暖季放牧和冷季放牧都显著改变了高寒草原化草甸土壤真菌群落系统发育结构,且暖季放牧也显著改变...     

人类放牧活动与气候变化对科尔沁沙质草地植物多样性的影响

为了解人类放牧活动和气候变化对我国北方沙质草地植物多样性的影响,笔者于1992-2006年在科尔沁沙地开展了草地放牧和封育试验,分析研究了人类放牧活动和降水、气温变化对草地植物多样性的影响.结果表明,1)放牧干扰对草地物种丰富度和多样性有着明显的影响,随着草地放牧干扰强度的增加,草地物种丰富度和植物多样性呈下降趋势,但只有持续重牧才会导致草地物种丰富度和多样性的明显降低;2)放牧干扰对草地不同生活型多样性和不同经济类群多样性的影响有很大差异,表现为随着放牧强度的增加,一年生植物多样性和禾本科植物多样性明显增加,多年生植物及菊科、藜科和杂类草植物多样性明显下降;3)不同放牧强度下的不同生活型多样性和经济类群多样性对气候变化的反应有很大差异,但除了重牧区菊科植物多样性与降水变化、中牧区杂类草植物多样性与气温变化达到显著相关外,其他相关性均未达到显著水平;4)在草地自然恢复演替过程中,暖湿气候有利于草地物种丰富度和多样性的增加,特别是可以明显促进多年生植物以及菊科、豆科植物多样性的增加,而持续暖干气候可以降低草地的物种丰富度和多样性,但对禾本科和藜科植物多样性的不利影响较小.     

短期放牧强度对半干旱草地植物群落多样性和生产力的影响

本文以晋北农牧交错带半干旱草地生态系统为研究对象,于2016年设置不放牧、轻度、中度和重度放牧4个不同放牧强度试验,研究短期放牧强度下羊对草地植物群落多样性与生产力的影响,以确定最佳放牧强度。研究结果表明,植物群落多度随放牧强度增加呈先升后降趋势,高度与盖度则随放牧强度的增加逐渐降低;物种多样性在中度放牧最高,重度放牧时最低;植物地上生物量随放牧强度增加呈抛物线形式变化,中度放牧时最高,分别为757.04 g·m^-2和398.37 g·m^-2,植物地下生物量随放牧强度增加逐渐降低;草地土壤容重随放牧强度的增加逐渐增大。短期放牧下中度放牧的植物群落多度、物种多样性与地上生物量最高,轻度放牧植物群落高度、盖度和地下生物量最高,重度放牧的物种多样性与生产力较低,因此适度放牧有利于保持草地植物群落稳定。     

Effects of pre-feeding of a corn silage-based supplement on the feed intake, milk production and nitrogen utilization of grazing dairy cows

Four Holstein cows were used to determine the effect of timing of the feeding of a corn silage (CS)‐based supplement on the feed intake, milk production and nitrogen utilization of grazing dairy cows. The cows were fed the supplement 2 h before grazing (pre‐grazing) or immediately after grazing (post‐grazing). Cows were grazed for 5 h per day under a rotational grazing system. There was no difference in the herbage and total feed intake between treatments. The milk protein yield for pre‐grazing tended to be higher than that for post‐grazing, whereas the milk yield did not differ between treatments. The total nitrogen intake for pre‐grazing tended to be higher than that for post‐grazing (P = 0.06). There was no difference in the urinary nitrogen output between treatments, whereas the proportion of urinary nitrogen output : total nitrogen intake for pre‐grazing tended to be lower than that for post‐grazing (P = 0.06). The milk nitrogen output and nitrogen retention for pre‐grazing tended to be higher than that for post‐grazing (milk nitrogen, P = 0.06; nitrogen retention, P = 0.05). Nitrogen utilization of grazing dairy cows was improved by feeding a CS‐based supplement before grazing.     

长期不同放牧强度下短花针茅荒漠草原物种多样性季节性动态变化

为揭示短花针茅（Stipa breviflora）荒漠草原物种多样性季节性动态变化对长期放牧强度的响应机制,本研究以内蒙古四子王旗短花针茅荒漠草原为研究对象,2018年5月至9月对围封14年（2004-2018）不同放牧处理下的物种组成、植物高度、盖度和密度进行观测,并对物种多样性、丰富度和均匀度分析。结果表明：5次观测对照区物种Shannon-Wiener多样性指数、Margalef丰富度指数均显著大于中度放牧区和重度放牧区;所有处理均是7月和8月的物种Shannon-Wiener多样性指数、Margalef丰富度指数较高,6月和9月观测值较小;Pielou均匀度指数变化差异由大到小排序为：重度放牧区 > 中度放牧区 > 轻度放牧区 > 对照样地;月份和放牧对短花针茅荒漠草原物种α多样性指数影响均达到极显著水平,且放牧处理对物种α多样性指数影响效应大于月份。研究认为,长期重度放牧对短花针茅荒漠草原物种多样性的影响在6月和9月表现最为明显,且会威胁草地生态系统的稳定性。     

放牧强度对环青海湖高寒草原群落物种多样性和生产力的影响

通过2年的连续放牧试验,采用比较样地法,调查了不同放牧强度对环青海湖高寒草原生物多样性和生产力的影响,并探讨了植物物种多样性与草地生产力之间的关系,为高寒草原的合理利用提供基础资料。结果表明:物种丰富度和多样性指数随放牧强度的增加基本呈单峰变化,即在中度放牧下多样性最高,重度放牧下群落物种丰富度、多样性指数和均匀度指数均表现为最小;群落生产力随放牧强度的增加而降低(P<0.05);莎草科地上生物量差异不显著,禾本科和豆科生产力降低(P<0.05),杂类草生物量有增加趋势;禾草和豆科比例减小,莎草和杂类草比例增加;草地生产力与Simpson多样性指数和Alatalo均匀度指数呈显著的单峰函数关系(R²=0.910, P=20.027; R²=0.953, P=20.010),结合Simpson多样性指数和Alatalo均匀度指数才能更好地反映维持草地生产力水平的多样性指标。放牧强度是影响群落物种多样性和生产力及其关系的重要因素。