Effects of livestock grazing on rangeland biodiversity: A meta‐analysis of grouse populations

Livestock grazing affects over 60% of the world's agricultural lands and can influence rangeland ecosystem services and the quantity and quality of wildlife habitat, resulting in changes in biodiversity. Concomitantly, livestock grazing has the potential to be detrimental to some wildlife species while benefiting other rangeland organisms. Many imperiled grouse species require rangeland landscapes that exhibit diverse vegetation structure and composition to complete their life cycle. However, because of declining populations and reduced distributions, grouse are increasingly becoming a worldwide conservation concern. Grouse, as a suite of upland gamebirds, are often considered an umbrella species for other wildlife and thus used as indicators of rangeland health. With a projected increase in demand for livestock products, better information will be required to mitigate the anthropogenic effects of livestock grazing on rangeland biodiversity. To address this need, we completed a data‐driven and systematic review of the peer‐reviewed literature to determine the current knowledge of the effects of livestock grazing on grouse populations (i.e., chick production and population indices) worldwide. Our meta‐analysis revealed an overall negative effect of livestock grazing on grouse populations. Perhaps more importantly, we identified an information void regarding the effects of livestock grazing on the majority of grouse species. Additionally, the reported indirect effects of livestock grazing on grouse species were inconclusive and more reflective of differences in the experimental design of the available studies. Future studies designed to evaluate the direct and indirect effects of livestock grazing on wildlife should document (i) livestock type, (ii) timing and frequency of grazing, (iii) duration, and (iv) stocking rate. Much of this information was lacking in the available published studies we reviewed, but is essential when making comparisons between different livestock grazing management practices and their potential impacts on rangeland biodiversity.     

内蒙古草原草场放牧退化模式研究及退化监测专家系统雏议

本文将定位研究与路线考察相结合,将放牧影响下草原的动态演替及其在牧压梯度上的空间变化相对比,研究了内蒙古主要草原草场的放牧退化模式,并在此基础上初步探讨了判别草场退化的数量指标和退化监测专家系统。1)植物种与牧压关系的分析,区别出放牧的定性和定量指示植物及宜中牧植物,并划分植物为不同的放牧生态种组。2)退化草原恢复过程的研究表明,根茎禾草的恢复快于丛生禾草;群落恢复过程是单稳态的,且恢复演替动态与其牧压梯度上的空间变化相对应。3)内蒙古高原主要草原草场在持续放牧影响下均趋同于冷蒿(Artemisia frigida)草原。冷蒿是最可靠的正定量放牧指示植物,但同时又是优良牧草和草原退化的阻击者。4)讨论了草原草场退化的概念,论述了草原逆向演替与草场退化的区别和联系,提出了区分草原的逆向演替为草场熟化和退化两个过程,并依草场群落与牧压的关系建立了判定草场是否退化及退化程度的数量指标。5)初步设计了草原草场退化监测—决策专家系统,包括监测、判别和决策三个步骤。     

Rangeland Mismanagement in South Africa: Failure to Apply Ecological Knowledge

Chronic, heavy livestock grazing and concomitant fire suppression have caused the gradual replacement of palatable grass species by less palatable trees and woody shrubs in a rangeland degradation process termed bush encroachment in South Africa. G razing policymakers and cattle farmers alike have not appreciated the ecological role fire and native browsers play in preventing bush encroachment. Unpredictable droughts are common in South Africa but have deflected too much blame for bush encroachment away from grazing mismanagement. Bush encroachment is widespread on both black and white farms, although the contributing socioeconomic, cultural, and political forces differ. Managers at Madikwe Game Reserve have reintroduced fire and native game animals into a formerly overgrazed system in an attempt to remediate bush encroachment, with encouraging preliminary results. A bush control program is needed that educates cattle farmers about the ecological causes of bush encroachment and encourages the use of fire and native browsers as tools for sustainable grazing management.     

Grassland-herbivore interactions: how do grazers coexist?

We develop a new approach to modeling grazing systems that links foraging characteristics (intake and digestive constraints) with resource dynamics via the probability of encounter with different grass heights. Three complementary models are presented: the generation of a grass height structure through selective grazing; investigating the conditions for consumer coexistence; and, using a simplified resource structure, the consequences for consumer abundance. The main finding is that coexistence between grazers differing in body size is possible if a single-resource type becomes differentiated in its height structure. Large grazers can facilitate food availability for smaller species but with the latter being competitively dominant. The relative preference given to different resource partitions is important in determining the nature of population interactions. Large-body and small-body grazer populations can interact through competitive, parasitic, commensalist, or amensalist relationships, depending on the way they partition the resource as well as their relative populations and the dynamics of resource renewal. The models provide new concepts of multispecies carrying capacity (stock equilibrium) in grazed systems with implications for conservation and management. We conclude that consumer species are not substitutable; therefore, the use of rangeland management concepts such as "livestock units" may be inappropriate.     

Ecology of grazing lawns in Africa

Grazing lawns are a distinct grassland community type, characterised by short‐stature and with their persistence and spread promoted by grazing. In Africa, they reveal a long co‐evolutionary history of grasses and large mammal grazers. The attractiveness to grazers of a low‐biomass sward lies in the relatively high quality of forage, largely due to the low proportion of stem material in the sward; this encourages repeat grazing that concomitantly suppresses tall‐grass growth forms that would otherwise outcompete lawn species for light. Regular grazing that prevents shading and maintains sward quality is thus the cornerstone of grazing lawn dynamics. The strong interplay between abiotic conditions and disturbance factors, which are central to grazing lawn existence, can also cause these systems to be highly dynamic. Here we identify differences in growth form among grazing lawn grass species, and assess how compositional differences among lawn types, as well as environmental variables, influence their maintenance requirements (i.e. grazing frequency) and vulnerability to degradation. We also make a clear distinction between the processes of lawn establishment and lawn maintenance. Rainfall, soil nutrient status, grazer community composition and fire regime have strong and interactive influences on both processes. However, factors that concentrate grazing pressure (e.g. nutrient hotspots and sodic sites) have more bearing on where lawns establish. Similarly, we discuss the relevance of enhanced rates of nitrogen cycling and of sodium levels to lawn maintenance. Grazer community composition and density has considerable significance to grazing lawn dynamics; not all grazers are adapted to foraging on short‐grass swards, and differences in body size and relative mouth dimensions determine which species are able to convert tall‐grass swards into grazing lawns under different conditions. Hence, we evaluate the roles of different grazers in lawn dynamics, as well as the benefits that grazer populations derive from having access to grazing lawns. The effects of grazing lawns can extend well beyond their borders, due to their influence on grazer densities, behaviour and movements as well as fire spread, intensity and frequency. Variation in the area and proportion of a landscape that is grazing lawn can thus have a profound impact on system dynamics. We provide a conceptual model that summarises grazing lawn dynamics, and identify a rainfall range where we predict grazing lawns to be most prevalent. We also examine the biodiversity associated with grazing lawn systems, and consider their functional contribution to the conservation of this biodiversity. Finally, we assess the utility of grazing lawns as a resource in a rangeland context.     

Population and clonal level responses of a perennial grass following fire in the northern Chihuahuan Desert

Relationships involving fire and perennial grasses are controversial in Chihuahuan Desert grasslands of southern New Mexico, USA. Research suggests that fire delays the resprouting of perennial grasses well after two growing seasons. However, such results are confounded by livestock grazing, soil erosion, and drought. Additionally, post-fire grass responses may depend on initial clone size. We evaluated the effects of fire, grazing, and clone size on Bouteloua eriopoda (black grama) in southern New Mexico grasslands. Four 2-ha plots were established in each of four sites. Fire and grazing were applied or not applied in 1999 such that four treatment combinations were assigned randomly to plots within each site. Within each plot, small (0–10 cm² basal area), medium (10–30 cm²), and large ( > 30 cm²) clones were initially mapped in five 0.91-m² quadrats where grass attributes and litter cover were evaluated before and at the end of two growing seasons following fire. Maximum fire temperature was also measured. At a population level, canopy and litter cover were each approximately 50% less in burned than unburned areas. However, compared to initial levels, canopy height had increased by 10% at the end of the study, regardless of fire. At a clonal level, basal cover reductions were attributed mostly to large clones that survived fire. Smaller clone densities had decreased by as much as 19% in burned compared to unburned areas, and fire reduced the basal cover of medium clones. Basal and canopy cover, recruitment, and clone basal area decreased with increased fire temperatures. Almost all responses were independent of grazing, and interactive effects of grazing and fire were not detected. Fire did not kill all perennial grass clones, regardless of size. However, rapid responses were likely influenced by above-average precipitation after fire. Future studies in desert grasslands should examine how perennial grass dynamics are affected by fire, precipitation patterns, and interactions with grazing.     

Sustainable Rangeland Grazing in Norse Faroe

The introduction of domestic livestock, particularly sheep, and rangeland grazing by Norse settlers to Faroe during the ninth century has generally been described as a major pressure on a sensitive landscape, leading to rapid and widespread vegetation change and contributing to land degradation. This view has, however, been developed without consideration of Norse grazing management practices which may have served to minimize grazing impacts on landscapes as well as sustaining and enhancing vegetation and livestock productivity. These alternative scenarios are considered using a historical grazing management simulation model with Faroese climate and vegetation inputs and given archaeological, historical and palaeoenvironmental parameters. Three contrasting rangeland areas are investigated and, based on the maximum number of ewe/lamb pairs the rangeland could sustain, modeling suggests that utilizable biomass declined with the onset of grazing activity, but not to a level that would cause major changes in vegetation cover or contribute to soil erosion even under climatically determined poor growth conditions. When rangeland areas partitioned into what are termed hagi and partir are modeled, grazing levels are still within rangeland carrying capacities, but productivities are variable. Some rangeland areas increase biomass and livestock productivities and biomass utilization rates while other rangeland areas that were too finely partitioned were likely to suffer substantial decline in livestock productivity. Partitioning of rangeland is a likely contributor to long-term differentiation of landscapes and the relative success of settlements across Faroe beyond the Norse period.     

Wildfire effects and post-fire responses of an invasive mesquite population: the interactive importance of grazing and non-native herbaceous species invasion

Aim To determine how responses of an established velvet mesquite (Prosopis velutina Woot.) population to a 2002 wildfire were shaped by grazing and non‐native herbaceous species invasions, both of which influenced fire behaviour. Location The study was conducted on contiguous ranches (one actively grazed by cattle, one that had not been grazed since 1968) in the Sonoita Valley of southern Arizona. Plant communities on both ranches were comprised of Chihuahuan semi‐desert grassland, savanna, and Madrean evergreen woodland ecosystems, but large areas were dominated by Lehmann and Boer lovegrass, African grass species that were introduced more than 50 years ago. Methods We selected 243 individuals that had been defoliated and bark scorched during the fire using a stratified random design based on pre‐fire grazing status and dominant grass cover. After the start of the 2003 growing season, we recorded individual tree characteristics, fire damage, and measures of post‐fire response, and tested for relationships among classes of: grazing status, bark damage, dominant grass cover type, abundance of live and dead aboveground branches, flowering status, and sprout number and size. Analyses of fire damage and post‐fire response were interpreted with respect to values of fireline intensity, scorch height and energy release that were projected by a fire behaviour model, nexus . Results Nearly all of the trees on grazed areas suffered low levels of fire damage, while a majority on ungrazed areas suffered moderate to severe damage. Trees on grazed areas consequently had significantly more leaf‐bearing twigs and branches in 2003 but a very low number of root sprouts, while individuals on ungrazed areas had a greater density of root sprouts but little post‐fire dead branching and almost no living branches. Among the ungrazed grassland types, more than 75% of the trees on Boer lovegrass plots suffered moderate to severe damage, while a similar percentage of trees in native grass areas suffered low damage. These differences were: (1) attributed to variations in fire characteristics that were caused by differences in litter production and removal, and (2) ecologically significant because trees in the severe damage class showed almost no aboveground post‐fire branching, either live or dead in 2003, while trees in the low damage class exhibited a greater amount of both. Main conclusions Our results affirm the notion that effective management of western grasslands where mesquite encroachment has or will become a problem requires a better understanding of how interactions among key ecosystem influences (e.g. fire, grazing, non‐native species) affect not only mesquite seedlings and saplings but also larger, established individuals and thereby the long‐term structure and functioning of semi‐desert grassland ecosystems. As managers shift their focus from eradication to management of mesquite in western grasslands and savannas, our results provide insights into how prescribed fires (and their effects on mesquite populations) differ from wildfires and how such effects may be mediated by the altered land uses and ecosystem characteristics that now exist in many western ecosystems.     

Leaf litterfall, fine-root production, and decomposition in shrublands with different canopy structure induced by grazing in the Patagonian Monte, Argentina

Selective sheep grazing in the Patagonian Monte induces the reduction of total and perennial grass cover, species replacement within life forms, and the increase in dominance of long-lived evergreen woody plants with slow growth rates and high concentration of secondary compounds in leaves. We hypothesized that these changes in the canopy structure induced by sheep grazing will affect the mass, chemistry and decomposability of leaf litter and fine roots. We selected two sites in the Patagonian Monte, representative of ungrazed and grazed vegetation states. At each site, we assessed canopy structure (total cover and absolute and relative grass and shrub cover), monthly leaf litterfall, and fine-root biomass and production in the upper soil (15 cm). We also estimated the rates of mass, C, soluble phenolics, lignin and N decay in litterbags containing both leaf litter and fine roots of each site under field conditions during two consecutive years. The ungrazed site exhibited higher total plant cover, absolute and relative grass- and shrub-cover than the grazed one. Leaf litterfall was lower at the grazed site than at the ungrazed site. Fine-root production did not vary between sites. Leaf litter and fine root tissues had higher concentration of secondary compounds at the grazed than at the ungrazed site. However, fine roots showed lower mass and C decay than leaf litter, attributable to the predominant secondary compound (lignin and soluble phenolics, respectively). Leaf litter decomposed slower but released more N during decay at the ungrazed than at the grazed site, probably due to its low concentration of secondary compounds. We concluded that changes in canopy structure induced by grazing disturbance such as those explored in our study could reduce leaf litterfall mass and increase the concentration of secondary compounds of both leaf litter and fine roots leading to slow N release to soil during decay.     

Intraspecific changes in plant morphology,associated with grazing,and effects on litter quality,carbon and nutrient dynamics during decomposition

Abstract: Continuous biomass removal by grazing usually changes the resource allocation pattern of plants. These changes often increase resistance to tissue removal and produce individuals with different morphometric traits, such as root to shoot or blade to sheath ratios. Shifts in morphometric traits, in turn, may alter nutrient cycling through changes in the average quality of litter that decomposes in soil. Previous work has shown that Paspalum dilatatum, a native grass from the Pampas grasslands, which inhabits a vast area and supports a wide range of grazing conditions, increases its blade to sheath ratio under continuous grazing with respect to ungrazed conditions. Here, we explored the consequences of these changes apparently associated with grazing regime on litter quality and nutrient dynamics during litter breakdown in soil. We separately analysed litter quality of blades and sheaths of P. dilatatum and determined under controlled conditions their decomposition and nutrient release kinetics over a maximum period of 1 year. We also studied the mineral nitrogen contents in soil amended with each litter type. Blade quality was significantly higher than sheath quality, nitrogen concentrations of blades and sheaths were approximately 1% and 0.6%, respectively, and lignin to nitrogen ratios were approximately 5 and 11 for blades and sheaths, respectively. Phosphorus concentration, however, was similar in both litter types. Blades decomposed 10% faster than sheaths, released 20% more nitrogen and released 15% more phosphorus than sheaths during the last half of the incubation period. During the first 3 months, the soil nitrogen content of litter‐amended incubations indicated immobilization with respect to non‐amended control; however, later blade incubations mineralized nitrogen, whereas sheath incubations continued immobilizing it. Results revealed that grazing potentially accelerates nutrient cycling during decomposition by increasing the blade to sheath ratio of P. dilatatum individuals, and suggest that this may be an important mechanism underlying grazing impact on nutrient cycling.     

放牧对青藏高原东部两种典型高寒草地类型凋落物分解的影响

为认识放牧对青藏高原东部中生性的高寒草甸草地和半湿生的沼泽草地凋落物分解的影响,在这两种草地上分别设置了围栏和放牧样地,研究了其各自的混合凋落物样品和4个优势物种(发草Deschampsiacaespitos、鹅绒委陵菜Potentilla anserine、木里苔草Carexmuliensis、藏嵩草Kobresiatibetica)凋落物的分解和养分释放动态,这4个优势物种也大致代表了当地沼泽草地生态系统在放牧和气候变暖驱动下逆行演替不同阶段的优势物种类群。结果表明,各优势物种凋落物的分解速率有显著差异;放牧在总体上促进了凋落物的分解,但不同物种的响应有所不同;放牧对凋落物C的释放影响不显著或有抑制作用,但对N、P的释放具有一定促进作用。对各优势物种凋落物分解和养分释放模式的分析表明,群落逆行演替过程中,凋落物分解和C释放加速,可能促进沼泽湿地退化的正反馈效应。草甸草地的退化标志物种鹅绒委陵菜具有较高的凋落物质量和分解速度,反映了中生条件下植物应对牲畜啃食采用"逃避"而非"抵抗"策略的趋向。     

Long-Term Grazing Accelerated Litter Decomposition in Northern Temperate Grasslands

Livestock grazing affects plant community composition, diversity, and carbon (C) and nutrient cycling in grasslands. Grazing leads to plant communities that have higher relative abundance of grazing-tolerant species, which in turn may alter the chemical composition of biomass and subsequent litter decomposition rates. To better understand the effects of long-term grazing and associated vegetation shifts on biogeochemical cycling in northern temperate grasslands of western Canada, we studied litter decomposition over 18 months at 15 locations, stratified across the Mixed-grass Prairie, Central Parkland, and Foothills Fescue natural subregions. At each location, we examined decomposition in an area exposed to grazing and an area where cattle were excluded. We used litterbags containing leaf litter from seven major grass species representing different grazing tolerances and included a local source of community litter from each study site and cellulose paper as standards. Decomposition was affected by litter types, with litter from grazing-tolerant species such as Poa pratensis and Bouteloua gracilis having faster decomposition rates compared to grazing-intolerant species, supporting the hypothesis that changes in vegetation composition due to grazing influences biogeochemical cycling by modifying litter decomposition in grasslands. Litter decomposition was also overall most rapid in the cool–wet Foothills Fescue, followed by the temperate mesic Central Parkland, and slowest in the warmer–drier Mixed-grass Prairie. Combined with known grazing-induced changes in grassland composition, these findings indicate that livestock grazing may accelerate litter decomposition rates in the more mesic Foothills Fescue and parkland regions, but not the more arid Mixed-grass Prairie. Overall, this study elucidates the role of livestock grazing and its associated effects on litter decomposition and ecosystem processes in northern grassland ecosystems.     

The importance of monkey beetle (Scarabaeidae: Hopliini) pollination for Aizoaceae and Asteraceae in grazed and ungrazed areas at Paulshoek, Succulent Karoo, South Africa

The relative importance of monkey beetles (Hopliini, Scarabeidae) as pollinators of Asteraceae and Aizoaceae in the Succulent Karoo as well as the influence of livestock grazing on their abundance and diversity was investigated. Hopliine beetles proved to be the, or among the, most abundant flower visitors of 12 investigated plant species. However, during single flower observations at three Aizoaceae species, bees (Apoidea), bee flies (Bombyliidae) and pollen wasps (Masaridae) were the most frequent flower visitors. However, monkey beetles carried the highest Asteraceae and Aizoaceae pollen loads, and are therefore considered to play a vital role in the pollination of these two families. Abundance, species richness and diversity of Hopliini did not appear to be heavily affected by livestock grazing. Annual variation in the composition of monkey beetle populations was more dramatic. Still, some species showed higher abundances on heavily grazed rangeland while others only occurred under low grazing pressure. It is presumed that changes in the composition of the vegetation, especially the observed decrease of perennial plants in favour of annuals and geophytes (Todd and Hoffman 1999) could in turn affect the composition of monkey beetle assemblages.     

Habitat use by Hen Harriers Circus cyaneus on Orkney: implications of land-use change for this declining population

The use of habitats by hunting Hen Harriers Circus cyaneus just prior to the settlement period was investigated on Orkney, where numbers have declined by 70% over the last 20 years. Both males and females hunted over areas that were closer to subsequent breeding territories. Neither sex differed in the amount of time they hunted over areas dominated by either intensive pasture, moorland or rough grazing. However, male hunting was significantly related to the amount of unmanaged grass habitat with a litter layer. Female hunting was related negatively to vegetation height, and to the prevalence of both Heather Calluna vulgaris and managed grass; after controlling for these habitat features, female hunting also tended to be associated negatively with Common Starling Sturnus vulgaris abundance. Dramatic changes in land use on Orkney have occurred over the last 40 years, with increases in the amount of intensive pasture and decreases in the amount of rough grazing. These changes, coupled with a doubling in sheep Ovis aries densities over the last 20 years, are likely to have reduced the amount of unmanaged grass. These changes will have been detrimental to hunting male Harriers by reducing the amount of food they can supply to the females prior to egg laying and during the incubation period.     

Defoliation and competition effects in a productivity gradient for a semiarid Mediterranean annual grassland community

Grazing and competition are two main factors shaping range plant communities; however, few studies have investigated their interaction. The current study aimed to investigate the effects of defoliation, competition and their interaction on production of annual grasses in semiarid Mediterranean areas. Competition treatments (absence/presence of neighbors) were combined with three defoliation intensities (0%, 30% and 60%) in a complete factorial design. Competition significantly reduced grass biomass. However, the role of competition was eliminated under heavy defoliation or under dry growth conditions. Defoliation showed variable results on final biomass (FB) and cumulative biomass (CB). While heavy defoliation (60% clipping intensity) reduced grass FB down to 80% during the two growing seasons, light defoliation (30%) significantly increased CB. Results showed that competition may limit the direct effect of defoliation on dominant grass species. Further, the relationship between site productivity and competition effect was best explained by a negative linear model. This hypothesized model may suggest that facilitation and competition alternatively affect grassland communities along a productivity gradient. The results suggest that light grazing may sustain or even enhance grassland productivity. The results also indicated the suitability of annual grass species to re-vegetate degraded rangeland in semi-arid climate. Further, optimum grazing practices to conserve biodiversity of Avena grassland may involve moderate stocking rate.     

Change in percentage ground cover of perennial grasses under different burning regimes

Summary Differences in the ground and perennial grass covers under different burning and grazing regimes are presented for three vegetation types in Kainji Lake National Park. It is shown from the results that perennial grasses established higher basal cover under late burning treatments than under early burning and no burning treatments. Late fires destroy litter which hinders grass growth while no burning treatments cause accumulation of litter. The highest number of grass tillers are produced under late burning treatments, while the lowest occurred under no burning treatments. The early burning plots have intermediate results. Occasional late burning in controlled small blocks of land is recommended for optimum grass production in the study area.Nomenclature follows Hutchinson & Dalziel 1954–1972. Flora of West Tropical Africa 2nd ed., edited by R.W.J. Keay & F.N. Hepper, Crown Agents, London.I am most grateful to Kainji Lake Research Institute for giving me great moral and financial support during the course of field work for this study. I am also very grateful to Dr. S.S. Ajayi of the Department of Forest Resources Management for allowing me to use part of his Senate Research Grant for the study.     

The effect of land management on carbon sequestration in salty rangelands of Golestan province,Iran

Land management is one of the most important factors affecting the protection and carbon sequestration of natural ecosystems. If the ecosystem is maintained naturally, it will have suitable vegetation and soil stability. One of the important factors that affects land management is livestock grazing. In order to evaluate the impact of exclosure rangeland on carbon sequestration (CS) in salty rangelands, the study was carried out in Inchehboroun rangelands of Golestan province, Iran. The main purpose of current research was to evaluate the effectiveness of management of salt rangeland on CS by topsoil and halophytes species. For this purpose, 40 plots (with 2 m² area) were located along 8 transects of 100 m in exclosure rangeland (ER) and grazing rangeland (GR) sites. The sampling method was randomized-systematic. In the area sampled, plant biomass was estimated. In addition, the content of above ground and underground biomass carbon, litter carbon, and soil organic carbon were determined for both ER and GR. The difference between the means was compared using Duncan test and t-test at P < 0.05. The result showed that the total CS for ER site was 15.02 ton/ha while it was 11.934 ton/ha in the case of GR. The total carbon sequestration (TCS) in ER was higher than the GR site. The CS of Halocnemum strobilaceum with 17.4 and 11.74% in ER and GR relatively was higher than that of other species. The results showed that the CS of shrubs in GR was lower than the ER site. The results revealed that the amount of C is affected by the land management in the production of OM and its degradation in the topsoil of salt rangeland. Aerial part of plants are the most important and sensitive part of an ecosystem that directly affects the C uptake and is also strongly influenced by the effect of animal grazing.     

Manipulation of vegetation communities on the Abu Dhabi rangelands. I. The effects of irrigation and release from longterm grazing

The effect on vegetation communities of release from grazing by camels and goats has been investigated in the Baynunah region of Abu Dhabi emirate, in The United Arab Emirates, by the study of an exclosure established 11 years previously. Also the effect of sprinkle irrigation (in the absence of grazing) on the rangeland vegetation was investigated. Perennial species richness was significantly lower outside the exclosure compared with inside on both sand and gravel substrata. Annual species richness however was not significantly different. Perrenial percentage covers were lower outside the exclosure compared with inside, especially on sand substrata. The perennial grass Stipagrostis plumosa (L) showed the greatest difference in percentage cover in this respect. The species richness of annuals and perennials was not significantly different between irrigated and non-irrigated areas within the exclosure. The perennial percentage cover was much greater on sprinkle irrigated sand and gravel substrata. The perennial which benefited the most was Zygophyllum hamiense, Scweinf. Annual percentage cover was lower in irrigated quadrats. Suggestions are made about the effect of intensive grazing on the vegetation communities at Baynunah and on the effectiveness of irrigation as a tool for increasing the quality of the rangeland for livestock and wildlife.     

稻田穗期主要捕食性天敌对两种盲蝽集团内捕食的初步研究

【目的】集团内捕食是影响农业系统广食性天敌对靶标害虫控制作用的重要因素,全面揭示稻田广食性天敌对稻飞虱重要天敌黑肩绿盲蝽Cyrtorhinus lividipennis Reuter和中华淡翅盲蝽Tytthus chinensis(St?l)(半翅目:盲蝽科)的集团内捕食作用有助于更好地保护利用天敌。【方法】建立以两种盲蝽为猎物对象的种特异性二重定量PCR系统,检测比较不同抗性品种穗期田间主要捕食者对两种盲蝽的集团内捕食作用。【结果】(1)本研究建立的二重定量PCR具有的物种专化性,两种检测靶标灵敏度高且相似,可用于田间捕食者猎物分析;(2)感虫水稻品种上捕食者对盲蝽的捕食强度高于抗性水稻品种;不同种类捕食者对盲蝽的集团内捕食强度有显著差异;捕食者对黑肩绿盲蝽集团内捕食强度显著高于中华淡翅盲蝽。【结论】捕食性盲蝽在稻田生态系统遭遇集团内捕食,其集团内捕食强度与水稻品种抗性、捕食者种类和猎物丰富度有关。     

Facilitation of a native pest of rice, Stenotus rubrovittatus (Hemiptera: Miridae), by the non-native Lolium multiflorum (Cyperales: Poaceae) in an agricultural landscape

Source populations of polyphagous pests often occur on host plants other than the economically damaged crop. We evaluated the contribution of patches of a non-native meadow grass, Lolium multiflorum Lam. (Poaceae), and other weeds growing in fallow fields or meadows as source hosts of an important native pest of rice, Stenotus rubrovittatus (Matsumura) (Hemiptera: Miridae), in an agricultural landscape of northern Japan. Periodical censuses of this mirid bug by using the sweeping method, vegetation surveys, and statistical analysis revealed that L. multiflorum was the only plant species that was positively correlated with the density of adult S. rubrovittatus through two generations and thus may be the most stable and important host of the mirid bug early in the season before the colonization of rice paddies. The risk and cost of such an indirect negative effect on a crop plant through facilitation of a native pest by a non-native plant in the agricultural landscape should not be overlooked.