The influence of Pechuel-Loeschea leubnitziae (wild sage) on grass sward and soil seed bank composition

Soil seed banks provide not only a historical record of vegetation composition but also the potential for post-disturbance revegetation. Pechuel-Loeschea leubnitziae (wild sage) is a multistemmed, aromatic shrub, occurring in Namibia, Botswana, Swaziland, Zimbabwe and the northern regions of South Africa, that colonises disturbed regions on sandy, alkaline soils. The influence of differing levels of P. leubnitziae cover on soil seed-bank characteristics and aboveground herbaceous species composition was determined by examining aboveground species composition, recorded in the field, and soil seed-bank species composition, determined by recording germinations from topsoil samples collected at each of 104 sites in the southern Okavango Delta. No correlation was observed between aboveground and soil seed-bank composition (p = 0.209). Cover of P. leubnitziae did not affect soil seed-bank species composition (p = 0.31) or the grass:non-grass ratio within the seed bank (p = 0.308). It did, however, affect aboveground grass composition (p = 0.018), with increasing P. leubnitziae cover associated with increasing abundance of poor-quality, shade-tolerant grass species. This confirms the observations that encroachment of P. leubnitziae may be associated with a decrease in veld quality and carrying capacity, and highlights the necessity for further study to facilitate a better understanding of the species for management purposes.     

Land use and dingo baiting are correlated with the density of kangaroos in rangeland systems

Rangelands worldwide have been subject to broadscale modification, such as widespread predator control, introduction of permanent livestock water and altered vegetation to improve grazing. In Australia, these landscape changes have resulted in kangaroos (i.e. large macropods) populations increasing over the past 200 years. Kangaroos are a key contributor to total grazing pressure and in conjunction with livestock and feral herbivores have been linked to land degradation. We used 22 years of aerial survey data to investigate whether the density of 3 macropod species in the southern rangelands of Western Australia was associated with: (i) land use, including type of livestock, total livestock, density of feral goats, type of land tenure, and kangaroo commercial harvest effort; (ii) predator management, including permitted dingo control effort, estimated dingo abundance, and presence of the State Barrier Fence (a dingo exclusion fence); and (iii) environmental variables: ruggedness, rainfall, fractional cover, and total standing dry matter. Red kangaroos (Osphranter rufus) were most abundant in flat, open vegetation, on pastoral land, where area permitted for dingo control was high, and numbers were positively associated with antecedent rainfall with a 12-month delay. Western grey kangaroos (Macropus fuliginosus) were most abundant on flat, agricultural land, but less abundant in areas with high permitted dingo control. Euros (Osphranter robustus) were most abundant in rugged pastoral land with open vegetation, where permitted dingo control was high. While environmental variables are key drivers of landscape productivity and kangaroo populations, anthropogenic factors such as land use and permitted dingo control are strongly associated with kangaroo abundance.     

The effects of topo-edaphic variables and cultivation on the woody vegetation of Weenen Nature Reserve,KwaZulu-Natal

The soil types and woody vegetation of Weenen Nature Reserve (WNR), KwaZulu-Natal, were described. Mispah, overlying shale, and Shortlands, overlying dolerite were the most common of 18 the soil forms encountered. Six vegetation types were identified by TWINS PAN which differed in slope, aspect, land-use history, species richness and tree density. Vegetation types ranged from species-rich, dense 'Coddia rudis-Dombeya cymosa Closed Woodland' overlying dolerite and occurring on steep north-east facing slopes that had never been cultivated, to previously cultivated, species-poor 'Acacia sieberiana Open Woodland' on flat topography, overlying shale. Ordination analyses further described the main associated floristic-environmental gradient from steep slopes supporting a high diversity of broad leaved species through to species-poor, flatter areas with an abundance of microphyllous plants. A second main gradient described was from uncultivated sites on steep slopes of usually dolerite-derived soils through to flat, previously cultivated land on shallow soils overlying shale. Topo-edaphic variables and previous cultivation, which were confounded, were therefore the main determinants of floristic variation in WNR, whereas fire had no influence. Half of the dominant woody species exhibited a reverse-J size structure, indicating relatively constant population change. A number of species had a preponderance of individuals in the smallest (0.5–1.5m height) size class, owing possibly to recruitment during the exceptional wet season of 1995/6, and/or the inability of individuals to escape the 'fire-trap'. Several, mostly Acacia, species appear to have recruited intermittently. The vegetation changes of this system will have an affect on browse availability. The woody vegetation of WNR appears to be changing in response to successional processes and management influences.     

Fuel Reduction,Seeding, and Vegetation in a Juniper Woodland

Western juniper has increased in density and distribution in the interior Pacific Northwest since the late 1800s. Management goals for many juniper woodlands are now focused on reducing tree densities and promoting biodiversity, prompting the use of fuel reduction treatments. Fuel reduction often involves mechanical cutting and disturbances such as slash pile burning and skid trail formation. While these activities may reduce tree densities, the extent to which they will restore native biodiversity and community composition, particularly in woodlands invaded by exotic annual grasses, is unclear. We evaluated the effects of juniper cutting in two experiments of disturbance type (slash piles and skid trails) followed by three native seeding treatments (cultivar, locally sourced, and no seed) on vegetation in central Oregon. Prior to cutting, native perennial grass cover and richness were positively associated and exotic grass cover was negatively associated with juniper basal area. After cutting and 2 yr after seeding, species composition was altered for both disturbance types. Some seeded areas had higher total species richness, higher native species richness, higher cover of seeded species, and higher overall cover compared to areas that were not seeded. But seeding effectiveness in mitigating exotic species spread varied based on exotic species functional group, pretreatment propagule pressure, and experiment disturbance type. Neither seed mix lowered exotic grass cover. There was limited evidence that the cultivar mix outperformed the locally sourced native seed mix. In the short term, fuel reduction activities may have facilitated further conversion of this woodland to an exotic grassland, but longer-term evaluation is needed. In juniper woodlands that have been invaded by exotic species, fuel reduction activities may facilitate further invasion, and exotic species control may be needed to limit invasion and promote native vegetation.     

Long-Term Effects of Fire,Livestock Herbivory Removal,and Weather Variability in Texas Semiarid Savanna

We examined how the occurrence and structure of grasses and woody plants changed after 12 yr of a fire season manipulation and removal of livestock herbivores. Applying high intensity fires in the summer preserved the structural integrity of this semiarid live oak (Quercus virginiana Mill.) savanna while decreasing or eliminating numerous problematic plants in the understory and overstory, such as prickly pear cactus (Opuntia spp.), sacahuista (Nolina texana S. Watson), Ashe juniper (Juniperus ashei J. Buchholz), Pinchot's juniper (J. pinchotii Sudw.), and honey mesquite (Prosopis glandulosa Torr.). In the less intense repeat winter burning treatments, undesirable woody plants were generally maintained at pretreatment levels in the overstory but all woody plants except Ashe juniper increased in the understory. Alternatively, areas excluded from fire in the control treatment rapidly transitioned from a grass-tree codominated savanna environment to one that is heavily dominated by woody plants. In the grass community, the most frequently occurring grass species in the winter burn treatment differed from summer burn and control treatments, whereas the summer burn treatment was not different from the control. Of the herbaceous plants, only little bluestem (Schizachyrium scoparium [Michx.] Nash) responded to fire treatments. Little bluestem increased in the winter burn treatment, remained fairly constant in the summer burn treatment, and decreased in the control. Other grasses varied largely as a function of annual weather variability, the removal of livestock, and legacy effects resulting from pre-existing variability. These findings suggest that fire can reduce or eliminate woody plant species that threaten the stability of live oak savannas while having little long-term effect on grasses desired by rangeland managers.     

Vegetation change over 40 years in the Weenen/Muden area,KwaZulu-Natal: evidence from photo-panoramas

The utility of panoramic photographs for studying the extent and pattern of vegetation change, in particular of bush encroachment, was investigated by revisiting thirteen sites in the Weenen and Muden areas of KwaZulu-Natal that had been photographed in 1955. The ubiquitous feature of all sites was the marked increase in woody cover, from a mean of 21% woody cover for all topographic units (plains, hill slopes, river bank and river terrace) in 1955, to 59% woody cover in 1998. Although sample sizes were small, the increase in woody cover was greater on hill slopes (45% mean increase in woody cover) than on the plains (26%), and on north-facing slopes (56%) rather than on south-facing slopes (32%). The increase in woody plant cover was accompanied by a change in composition from open or mixed woodland, to one dominated by Acacia species, in particular by A. tortilis at lower altitudes and by A. karroo at higher altitudes. In some cases, scrub Acacia individuals were already evident in the photographs in 1955, and had grown into mature trees by 1998. Recruitment of both Acacia and broad-leafed species was also observed in 1998 and there was a tendency for bush clumps to develop. Broad-leafed species have dominated on moist south-facing slopes and at higher altitudes. Increases of the arborescent leaf succulents. Aloe spectabilis and Opuntia ficus-indica and of the dwarf, stem succulent shrub, Euphorbia pseudocactus, have occurred. Fire is no longer a component of this landscape which, together with the open condition in 1955, resulting from overgrazing. may account for the vegetation changes that have taken place. Panoramic photographs proved an effective tool for monitoring vegetation change because changes in composition and structure were revealed, and because each photograph samples a large area of ground at an adequate resolution.     

Assessing the Carbon Consequences of Western Juniper (Juniperus occidentalis) Encroachment Across Oregon,USA

Our ability to assess the continental impacts of woody encroachment remains compromised by the paucity of studies quantifying regional encroachment rates. This knowledge gap is especially apparent when it comes to quantifying the impact of woody encroachment on large-scale carbon dynamics. In this study, we use a combination of aerial photography from 1985–1986 and 2005 and near-annual Landsat satellite imagery over the same period to assess the rates of encroachment by western juniper, Juniperus occidentalis Hook., into the grasslands and shrublands of eastern Oregon. The approximately 20-yr Landsat reflectance trajectories identified for the juniper woodlands of eastern Oregon did not correlate well with changes in juniper crown cover over the same period, suggesting that systematic trends in reflectance are being driven by vegetation other than juniper. Using a random sample of 150 aerial photography plots, we estimate the average aboveground accumulation of carbon in undisturbed juniper woodlands to be 2.9 kg C · m^-2 · yr^-1; about 0.20 Tg C · yr^-1 across all of Oregon. However, juniper removal by cutting and or burning, occurring at a rate of < 1% yr^-1, counteracted regional encroachment by about 35%, bringing the net change in aboveground carbon down to 1.9 kg C · m^-2 · yr^-1, about 0.13 Tg C · yr^-1 across all of Oregon. This study illustrates the capacity of woody removal, over very small areas, to offset encroachment over very large areas and cautions against scaling site-level encroachment studies over entire regions.     

Grazing Intensity Influences Ground Squirrel and American Badger Habitat Use in Mixed-Grass Prairies

Ground squirrel (Spermophilus spp.) and American badger (Taxidea taxus) burrowing activities are ecologically important disturbances that contribute to the heterogeneity of prairie environments. These activities also have a strong impact on habitat suitability for many other grassland species. However, effects of cattle grazing intensity on ground squirrel and American badger burrows are not well understood. From 2006 to 2012 we evaluated effects of grazing intensity and vegetation type on American badger burrow occurrence and ground squirrel burrow abundance using a manipulative grazing experiment in Grasslands National Park of Canada, Saskatchewan. The study area consisted of nine 300-ha pastures at a range of stocking rates, from very low to very high for the region. Each pasture had 10 plots (six upland and four lowland) where vegetation and burrow surveys were completed. Burrow abundance and occurrence as well as vegetation structure were assessed for 2 yr prior to the introduction of cattle to this landscape in 2008, which followed at least 15 yr without livestock, and from 2009 to 2012, following introduction of livestock. Data were analyzed using generalized linear mixed models. In upland habitats, ground squirrel burrow counts increased with increasing grazing intensity and decreasing vegetation biomass; conversely, badger burrow occurrence increased with decreased stocking rates and increasing average litter cover and vegetation biomass. Abundance and occurrence of both ground squirrel and badger burrows in lowland habitats was relatively independent of grazing intensity or vegetation. Vegetation composition had little impact on ground squirrel or badger burrows. A range of grazing intensities may contribute to maintaining diversity of burrowing mammals in prairie environments.     

Effect of Pinyon–Juniper Tree Cover on the Soil Seed Bank

As pinyon–juniper (specifically, Pinus monophylla and Juniperus osteosperma) woodlands in the western United States increase in distribution and density, understory growth declines and the occurrence of crown fires increases, leaving mountainsides open to both soil erosion and invasion by exotic species. We examined if the loss in understory cover that occurred with increasing tree cover was reflected in the density and diversity of the seed bank. Seed banks in stands with low, medium, and high tree cover were measured in late October for 2 yr. Multivariate analyses indicated that cover and diversity of standing vegetation changed as tree cover increased. However, the seed bank did not differ in overall seed density or species diversity because seeds of the 13 species that comprised 86% of the seed bank occurred in similar density across the tree-cover groups. Sixty-three percent of the species that were in the seed bank were absent from the vegetation (mostly annual forbs). In addition, 49% of the species that occurred in the standing vegetation were not in the seed bank (mostly perennial forbs and shrubs). Only Artemisia tridentata, Bromus tectorum, and Collinsia parviflora displayed positive Spearman rank correlations between percent cover in the vegetation and density in the seed bank. Thus, much of the standing vegetation was not represented in the seed bank, and the few species that dominated the seed bank occurred across varying covers of pinyon–juniper.     

Indigenous Rangeland and Livestock Management Among Pastoralists and Agro-pastoralists in Miombo Woodlands,Eastern Tanzania

Indigenous rangeland management practices, forage quality and availability, and livestock production by pastoralists and agro-pastoralists in miombo woodlands were investigated in a study conducted in Kilosa district, Tanzania. The study methods comprised household interviews, key informant and focus group discussions, and forage laboratory analyses. Preferred forage species and indigenous rangeland and livestock management practices among pastoral and agro-pastoral communities in miombo woodlands were identified, and the nutrient content of the forages was determined. In general, rangeland management in the study area faces challenges such as unclear or disputed land tenure regime and lack of technical knowledge. Moreover, the nutritional value of some native forage species identified in miombo was found to be too low to meet the nutrient requirements of livestock. Livestock in miombo contribute greatly to household livelihoods and food security, but forage scarcity was identified as a limiting factor. Overall, it was concluded that rangeland improvement practices are poor or nonexistent in allocated grazing areas in Kilosa’s miombo woodlands.     

The effect of tebuthiuron on the vegetation of the thorn Bushveld of the Northern Cape – a preliminary report

Abstract

Two formulations of tebuthiuron i.e. Graslan 20P and Graslan 40P are currently being evaluated in the Molopo area. Tebuthiuron was applied aerially at ten application rates, in combination with two application dates.

After only two seasons, the chemical has already shown a reasonable selectivity for the woody species. Of these, Acacia mellifera, A. reficiens and Grewia flava are very sensitive while A. erioloba and Dichrostachys cinérea are less sensitive and Boscia albitrunca seems almost resistant to the lower application rates (<1,0 kg a.i./ha).

The standing crop of grass on the treated plots increased by between 220 and 740 per cent. Changes in the total grass density and botanical composition can be ascribed to an increased density of Eragrostis lehmanniana.

At this stage of the trial, its selectivity in favour of the more desirable woody species, suggests that tebuthiuron shows great promise for controlling bush encroachment in the Northern Cape, although a final conclusion would only be possible 5 years after its application.     

Long-Term Response Patterns of Tallgrass Prairie to Frequent Summer Burning

Knowledge of how tallgrass prairie vegetation responds to fire in the late growing season is relatively sparse and is based upon studies that are either spatially or temporally limited. To gain a more robust perspective of vegetation response to summer burning and to determine if repeated summer fire can drive vegetational changes in native tallgrass prairie, we evaluated species cover and richness over a 14-yr period on different topographic positions from ungrazed watersheds that were burned biennially in the growing season. We found that annual forbs were the primary beneficiaries of summer burning, but their fluctuations varied inconsistently among years. Concomitantly, species richness and diversity increased significantly with summer burning but remained stable through time with annual spring burning. After 14 yr, species richness was 28% higher in prairie that was burned in the summer than in prairie burned in the spring. Canopy cover of big bluestem (Andropogon gerardii Vitman) and Indiangrass (Sorghastrum nutans [L.] Nash) increased significantly over time with both summer and spring burning, whereas heath aster (Symphyotrichum ericoides [L.] Nesom), aromatic aster (Symphyotrichum oblongifolium [Nutt.] Nesom), and sedges (Carex spp.) increased in response to only summer burning. Kentucky bluegrass (Poa pratensis L.) cover declined in both spring-burned and summer-burned watersheds. Repeated burning in either spring or summer did not reduce the cover or frequency of any woody species. Most perennial species were neutral in their reaction to summer fire, but a few species responded with large and inconsistent temporal fluctuations that overwhelmed any clear patterns of change. Although summer burning did not preferentially encourage spring-flowering forbs or suppress dominance of the warm-season grasses, it is a potentially useful tool to increase community heterogeneity in ungrazed prairie.     

基于地理探测器模型的川西北家畜空间分布差异影响因素分析

川西北放牧家畜分布具有空间尺度分异的特征,以乡镇为单位的基础数据,在研究自然和人为因素对家畜空间分布的影响方面,有助于得出更细致、更客观的结果,将为川西北地区畜群结构的优化提供科学依据.试验以气象、地形、植被类型、植被覆盖度、土地利用类型、人口、出栏管理等方面的数据为基础,利用GIS空间分析和地理探测器模型相结合的方法...     

Molecular and Statistical Analysis of Campylobacter spp. and Antimicrobial‐Resistant Campylobacter Carriage in Wildlife and Livestock from Ontario Farms

The objectives of this study were to (i) compare the carriage of Campylobacter and antimicrobial‐resistant Campylobacter among livestock and mammalian wildlife on Ontario farms, and (ii) investigate the potential sharing of Campylobacter subtypes between livestock and wildlife. Using data collected from a cross‐sectional study of 25 farms in 2010, we assessed associations, using mixed logistic regression models, between Campylobacter and antimicrobial‐resistant Campylobacter carriage and the following explanatory variables: animal species (beef, dairy, swine, raccoon, other), farm type (swine, beef, dairy), type of sample (livestock or wildlife) and Campylobacter species (jejuni, coli, other). Models included a random effect to account for clustering by farm where samples were collected. Samples were subtyped using a Campylobacter‐specific 40 gene comparative fingerprinting assay. A total of 92 livestock and 107 wildlife faecal samples were collected, and 72% and 27% tested positive for Campylobacter, respectively. Pooled faecal samples from livestock were significantly more likely to test positive for Campylobacter than wildlife samples. Relative to dairy cattle, pig samples were at significantly increased odds of testing positive for Campylobacter. The odds of isolating Campylobacter jejuni from beef cattle samples were significantly greater compared to dairy cattle and raccoon samples. Fifty unique subtypes of Campylobacter were identified, and only one subtype was found in both wildlife and livestock samples. Livestock Campylobacter isolates were significantly more likely to exhibit antimicrobial resistance (AMR) compared to wildlife Campylobacter isolates. Campylobacter jejuni was more likely to exhibit AMR when compared to C. coli. However, C. jejuni isolates were only resistant to tetracycline, and C.  coli isolates exhibited multidrug resistance patterns. Based on differences in prevalence of Campylobacter spp. and resistant Campylobacter between livestock and wildlife samples, and the lack of similarity in molecular subtypes and AMR patterns, we concluded that the sharing of Campylobacter species between livestock and mammalian wildlife was uncommon.     

Mixed livestock grazing in diverse temperate and semi-arid environments

The need for an annual increase of 2% in global food production demands knowledge on how best to use natural grazing land resources. Taken with the requirement to protect resources, this need creates conflicting demands on grazing land management. Concerns for product quality, uniformity and continuity and for animal welfare will increasingly drive production processes. In this paper, the potential of mixed grazing for higher output of quality animal products, within these constraints, is assessed under both temperate and semi-arid conditions. Complementary behavioural patterns between domestic livestock types, particularly in their dietary selection, appear to be the primary basis for development of improved grazing ecosystems. Many of these processes operate at the landscape scale. In addition to increasing animal output, mixed grazing can be used to modify the vegetation. This is of particular importance for manipulating woody species cover in semi-arid areas and hence for improvement of range condition. For rural development, identification with the system and confidence in the purveyor sets the basis for success.     

Trial by fire: social spider colony demographics in periodically burned grassland

Nature conservation authorities in southern Africa burn the grassland in nature reserves to reduce the incursion of woody plants and to encourage the growth of new grass for grazing. Studies have shown significant negative effects of burning on the abundance, species diversity and community composition of smaller vertebrates and invertebrates. Social arthropods are likely to suffer from repeated burning, as destruction of the colony means a permanent loss of the entire reproductive unit. Nests of social spiders of the genus Stegodyphus (Eresidae) are a prominent feature of African savannas and their size and visibility make them potentially good indicators of ecological consequences of fire. The colonies are sedentary and their nests may persist for several years, although individuals have an annual life cycle. We explored the mortality patterns and the effects of burning on survival of colonies of two species of social spider, Stegodyphus mimosarum and S. dumicola that live sympatrically. We compared colony mortality in burned and unburned areas to determine if colony mortality was due to burning or, alternatively, to natural senescence. Analysis of five years of nest mortality data together with information on the burning regime in Spioenkop Nature Reserve, KwaZulu Natal province (South Africa), indicates that colony extinction in S. mimosarum is independent of the burning regime, while burning is a significant cause of colony mortality in S. dumicola. The different responses of the two species are likely a result of different colony dynamics and nesting sites.     

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.     

Plant and Small Vertebrate Composition and Diversity 36–39 Years After Root Plowing

Root plowing is a common management practice to reduce woody vegetation and increase herbaceous forage for livestock on rangelands. Our objective was to test the hypotheses that four decades after sites are root plowed they have 1) lower plant species diversity, less heterogeneity, greater percent canopy cover of exotic grasses; and 2) lower abundance and diversity of amphibians, reptiles, and small mammals, compared to sites that were not disturbed by root plowing. Pairs of 4-ha sites were selected for sampling: in each pair of sites, one was root plowed in 1965 and another was not disturbed by root plowing (untreated). We estimated canopy cover of woody and herbaceous vegetation during summer 2003 and canopy cover of herbaceous vegetation during spring 2004. We trapped small mammals and herpetofauna in pitfall traps during late spring and summer 2001–2004. Species diversity and richness of woody plants were less on root-plowed than on untreated sites; however, herbaceous plant and animal species did not differ greatly between treatments. Evenness of woody vegetation was less on root-plowed sites, in part because woody legumes were more abundant. Abundance of small mammals and herpetofauna varied with annual rainfall more than it varied with root plowing. Although structural differences existed between vegetation communities, secondary succession of vegetation reestablishing after root plowing appears to be leading to convergence in plant and small animal species composition with untreated sites.     

An Assessment of Nonequilibrium Dynamics in Rangelands of the Aru Basin,Northwest Tibet,China

An assessment of nonequilibrium rangeland dynamics was conducted in the Aru basin, a semiarid site located in the very dry northwest part of the Chang Tang Nature Reserve, Tibet, China. A grazing gradient approach was used to examine the effects of different livestock grazing intensities on vegetation, providing data to determine if plant–herbivore interaction has been a major structuring force of the plant community and thus to indicate what type of dynamic might apply in the study area. No significant differences were found between a highly grazed site and a lightly grazed site in vegetation cover, standing biomass, and Shannon–Wiener species diversity index of total, graminoid, forb, and tomtza (Oxytropis glacialis Benth. ex Bunge) functional groups, with the exception that tomtza coverage was significantly higher at the highly grazed (1.04%) than at the lightly grazed site (0.02%). Grazing intensity alone did not explain a significant amount of variation in the plant species data. These results indicate that a dominance of nonequilibrium dynamics appears to be the case in the basin, probably one of the least-arid sites in the northwest Chang Tang region of the Tibetan Plateau. Thus, opportunistic livestock management strategies adapted to variable vegetation production from year to year, rather than the setting of a rigid stocking rate that assumes a stable carrying capacity, is probably the most plausible approach for managing livestock and its relationship to biodiversity values in this region.     

Macro and trace elements of 26 browse species growing in semi-arid grazing lands of Eastern Cape,South Africa

ABSTRACT

Leaves and twigs from woody plants provide essential nutrients to range animals. We examined variation in the mineral status of 26 woody species, and the influence of harvesting height as well as the interactions of the main effects on minerals levels. Leaves were harvested from five individual plants per species at two height levels: low (<1 m) and upper (>1.5 m). For trees, all mineral levels showed variation (p < 0.05) between species. For shrubs and intermediate growth forms (between shrubs and trees), mineral levels except potassium (K) and zinc (Zn) were influenced (p < 0.05) by height × species interactions. Most browse species had calcium (Ca) contents (8.5–50 g kg^-1) above the required levels, with the majority of the species having Ca beyond the maximum tolerable limit. Most browse plants had sufficient K, phosphorus, magnesium, manganese, iron and Zn concentrations to meet the requirements for ruminants. Copper was deficient in many browse leaves, thus supplementation should be considered in winter. We conclude that such knowledge is essential for sustainable use of browses as mineral supplements, especially during critical periods when climatic conditions limit the feed value of grasses.