Comparison of biodiversity and ground cover between a commercial rotationally grazed property and an adjacent nature reserve in semi‐arid rangeland

Continuous livestock grazing can have negative effects on biodiversity and landscape function in arid and semi‐arid rangelands. Alternative grazing management practices, such as rotational grazing, may be a viable option for broad‐scale biodiversity conservation and sustainable pastoral management. This study compared ground cover, plant species composition and floristic and functional diversity along gradients of grazing intensity between a pastoral property rotationally grazed by goats and an adjacent nature reserve (ungrazed by commercial livestock) in semi‐arid south‐eastern Australia. Understorey plant species composition differed significantly between the rotationally grazed property and the nature reserve, with a greater proportion and frequency of palatable species recorded in the nature reserve. Understorey plant species richness, diversity, functional biodiversity measures and ground cover declined with increasing grazing pressure close to water points under commercial rotational grazing management. However, at a whole‐paddock scale, there were few differences in plant biodiversity and ground cover between the rotationally grazed property and the nature reserve, despite differences in overall plant species composition. Flexible, adaptive, rotational grazing should be investigated further for its potential to achieve both socio‐economic and biodiversity conservation outcomes in semi‐arid rangelands to complement existing conservation reserves.     

水源圈研究进展

在干旱、半干旱区草场上,由于饮水的需求导致牲畜经常性地集中在水源点周围,从而使草地生态系统以水源点为中心呈梯度退化,形成水源圈.按照放牧影响程度的大小,以水源点为中心由内向外可将水源圈划分为“牺牲带”、过渡带和自然带3部分,水源圈内的植被、土壤等对放牧的响应也呈梯度变化.由于水源圈内存在着“天然的放牧梯度”,使其成为研究放牧对植被、土壤的影响和自然资源保护及其可持续利用的绝佳场所.本文对水源圈的概念、研究的发展历程和研究方法等进行了综述,并对国内研究现状进行了评述,以促进干旱、半干旱区草场的科学管理和可持续利用.     

Spatial variation in the demography and population dynamics of a perennial shrub (Atriplex vesicaria) under sheep grazing in semi‐arid Australian rangelands

Atriplex vesicaria Heward ex Benth. (Chenopodiaceae) is a widespread perennial shrub in southern Australia's chenopod rangelands but is sensitive to grazing. A detailed investigation of the demography and population dynamics of A. vesicaria under sheep grazing was conducted over 6.5 years at a range of sites across a typical paddock to assess the long‐term effects of grazing on the species and elucidate the mechanisms of population change under grazing. The effects of rainfall on recruitment and mortality were also examined. Six‐monthly censuses of all A. vesicaria individuals were conducted in permanent grazed and ungrazed plots at sites located across an 1100‐ha paddock. Grazing increased adult shrub mortality close to water and reduced recruitment over a broader area of the paddock, but seedling survival did not appear to be affected by grazing. As a result of these changes, the population declined on grazed plots up to 2200 m from water during the study, but the decline was greatest closer to water. The population was most dynamic at the sites furthest from the water point where it was unaffected by grazing because of the greater recruitment and mortality of young plants, but because these processes balanced out over time, population density was effectively unchanged by the end of the study. Although statistical models indicated that six‐monthly rainfall did not explain temporal variation in recruitment or mortality, rainfall nevertheless has a central role in both processes. In particular, longer periods of favourable rainfall and drought appear to have an important influence on recruitment and mortality, respectively, with heavy grazing during a drought period increasing mortality. Occasional shortages of seed or rains occurring during the warmer months when seed germination is limited possibly explain poor recruitment at sites unaffected by grazing following good rainfall.     

Long-term effects of daily grazing orbits on nutrient availability in Sahelian West Africa: 2. Effects of a phosphorus gradient on spatial patterns of annual grassland production

Abstract. This paper reports on an investigation of the effect of a livestock-generated gradient in phosphorus-availability on spatial patterns of annual rangeland production around pastoral watering points in the Sahelian region of West Africa. The study was conducted along a major transhumance corridor used for at least the past century by herds managed by agropastoralists of the Inland Niger Delta of Mali. Eighteen sites on sandy substrate were established at varying distances from: (1) a more persistent pan from which livestock disperse to graze primarily during the early dry season (D1); and (2) a line of ephemeral pans from which livestock disperse to graze during the rainy season (D2). Data on the species composition, standing herbaceous mass, and annual herbaceous cover were collected at these sites over the 2 years following a significant drought. These vegetative parameters show considerable interannual variation in their spatial pattern. As reported elsewhere (companion paper), chemical analyses of soil and plant samples collected at these sites show a significant negative correlation between phosphorus availability and D2. This is consistent with livestock-mediated nutrient transfer from outlying zones toward rainy-season pans. The effect of this phosphorus gradient on annual rangeland production was analysed using a regression modelling approach. Two vegetative production parameters, vegetated surface fraction (VSF) and herbaceous above-ground standing mass of vegetated surface (VAGM), were regressed in a two-and three-step process on the following factors: (1) background soil and rainfall data; (2) forb fraction of herbaceous production (for VAGM only), followed by: (3) D1 and D2. These analyses find that while the phosphorus-availability gradient had a significant effect on spatial patterns of herbaceous production during the year immediately following the drought, it had little effect in the subsequent year's production. This difference is explained by the increased importance of nitrogen in limiting herbaceous production during the second year, resulting from its different rainfall history.     

Using ants to manage sustainable grazing: Dynamics of ant faunas along sheep grazing gradients conform to four global patterns

Ants are considered an important faunal group for the functioning of arid rangelands, they have a long history of use for environmental monitoring, and exhibit four global patterns in grazing lands: (i) soil and vegetation type are primary determinants of ant community composition, and have a far greater effect on ant community composition than grazing; (ii) grazing induces species compositional change, but does not necessarily affect species richness or abundance; (iii) a species response to grazing is not necessarily consistent across habitats; and (iv) approximately one‐quarter to one‐half of species that are common enough for statistical analysis have significant responses to grazing. Here we report the patterns of arid zone ant faunas as they exist after several decades of sheep grazing in southern Australia, and examine the extent to which they conform to the four global patterns. We measured ant faunas along grazing gradients (varying distance to water) in seven paddocks containing two soil and two vegetation types on five pastoral properties. Total site abundance and richness of ants did not differ significantly with distance from water, but the abundance of 10 (34%) of the 29 most common species did differ; three were increasers, three were decreasers, and four had mixed responses dependent on soil/vegetation type. Rare species showed no trend with grazing intensity. The ant fauna of the more structurally complex vegetation types appeared to be the most vulnerable to grazing effects. Multivariate analysis showed soil type was the primary factor influencing ant faunal composition, followed by vegetation structure; however, grazing treatment effects were present. This study fully supports the recently identified global patterns of ant responses to grazing. It also shows that sampling regional ant faunas using widely dispersed traps can detect ant faunal patterns comparable to studies that use smaller‐scale grids of traps.     

Water distribution at local and landscape scales affects tree utilization by elephants in Chobe National Park,Botswana

African elephant distribution and impacts are influenced by water availability. This study investigates the formation of piospheres – gradients of vegetation degradation with increasing proximity to water – at local and landscape scales in Chobe National Park, Botswana. Thirty‐four plots record elephant impact on trees in a transect extending over 60 km from the Chobe River, differentiating between debarking and browsing on branches. Elephant utilization exhibits local patterns nested within a landscape‐level context. At a local scale, branch herbivory decreases with distance from water, while debarking first decreases and then increases again. At a landscape scale, regression and canonical correlation analyses show decreasing debarking with distance from the river. Surprisingly, branch herbivory increases with distance from river, except within the first 10 km where previous studies have focused. Elephant impact on vegetation is both more complex and extensive than previously assumed. Piosphere predictions are upheld at the local scale, with utilization decreasing with distance from water. This does not hold at the landscape scale, however, likely due to seasonal shifts in elephant distribution, diet and the presence of water in ephemeral pans. These findings have important implications for elephant management and emphasize the importance of looking across scales when assessing elephant impact.     

水源圈研究进展

在干旱、半干旱区草场上,由于饮水的需求导致牲畜经常性地集中在水源点周围,从而使草地生态系统以水源点为中心呈梯度退化,形成水源圈.按照放牧影响程度的大小,以水源点为中心由内向外可将水源圈划分为“牺牲带”、过渡带和自然带3部分,水源圈内的植被、土壤等对放牧的响应也呈梯度变化.由于水源圈内存在着“天然的放牧梯度”,使其成为研究放牧对植被、土壤的影响和自然资源保护及其可持续利用的绝佳场所.本文对水源圈的概念、研究的发展历程和研究方法等进行了综述,并对国内研究现状进行了评述,以促进干旱、半干旱区草场的科学管理和可持续利用.     

Ecological impact of large herbivores on the woody vegetation at selected watering points on the eastern basaltic soils in the Kruger National Park

A lack of quantitative data on the impact of large herbivores on woody vegetation around watering points in the Kruger National Park gave rise to an in depth study. This paper reports on trends found at two artificial watering points on the basaltic soils in the Satara Land System. As a result of the almost complete lack of woody individuals in the immediate vicinity of the watering points, this area could be described as a 'sacrifice area'. Shrub density increased with distance from the watering point, with the impact of large herbivores on shrub density extending up to 2.8 km. The practice of providing artificial water in troughs at windmills in the Kruger National Park causes the formation of a multiple 'piosphere' effect, with the existence of a zone of high utilization in woody vegetation extending far beyond the sacrifice area.     

Correlations of stocking with the cryptogamic soil crust of a semi-arid rangeland in southwest Queensland.

Abstract The soil crust community from a sub-tropical grassland in southwest Queensland was found to include 34 taxa with cyanobacteria, other algae, lichens, fungi, mosses and liverworts represented. Cyanobacteria and liverworts were the major components of the cryptogamic cover. This is a significant component of the biodiversity of the region. Changes in the structure of this community were significantly correlated with distance from a linear water supply (bore drain) and with dung density. It was concluded that hoof impact by grazing stock had measurably affected the cryptogamic community even under a moderate stocking policy. This research suggests that management for sustainable use of low-nutrient rangelands should include consideration of soil crust condition.