The lack of consensus regarding potentially detrimental effects of livestock grazing on rangelands is epitomised in two papers from Sahelian Africa. Discussion about the relative merits of the two approaches to understanding rangeland dynamics has been intensified when the debate progresses to encompass views on how best to manage grazing in rangelands.
In this context, both natural and social sciences are represented since the focus is on the sustainability of pastoralist land use. Views on the sustainability of grazing have also diverged, largely reflecting the different ideas on rangeland ecology. This view argues that traditional pastoralists frequently graze their livestock in unsustainable numbers because they pursue their short-term survival at the expense of the long-term conservation of commonly owned natural resources. The opposing view adopts a non-equilibrium understanding of rangelands, in which grazing has only a marginal influence on vegetation dynamics.
In the former approach, traditional pastoralism is seen as unsustainable and in need of modernisation Lamprey The latter view leads to the opposite conclusion: pastoralist land use practices are an effective and sustainable response to the highly variable natural environment Behnke et al. Most arid and semiarid rangelands encompass elements of both equilibrium and non-equilibrium approaches and both grazing and variable rainfall are important drivers of vegetation dynamics on different temporal and spatial scales Vetter ; Gillson and Hoffman Hence, any sustainable approach to management must take account of temporal variability and spatial heterogeneity Joly et al.
Of course there are also many nuances to a debate that is frequently presented in simple dualistic terms. The notion that a certain level of grazing has the effect of enhancing plant productivity has a considerable history, although plants respond to a whole suite of environmental factors, and the variety of plant responses is subject to the constraints of plant genetics, developmental stage and the plant tissues affected McNaughton Further, different plants respond to being eaten by animals in different ways Matches Similarly, different species of domestic livestock have different forage demands and foraging behaviours and can therefore reasonably be expected to have different impacts on vegetation communities.
One form of vegetation change that is commonly associated with heavy grazing in some grasslands is an increase in biomass and abundance of woody plant species that are frequently thorny or unpalatable, with the suppression of herbaceous plant cover. The direct defoliation effects of grazing or browsing are just one set of impacts associated with livestock.
Soil surfaces and soil profiles are materially affected by compaction caused by animal trampling, and excretion by grazing animals has impacts on vegetation, soils and surface waters Bilotta et al. The time and space scales of observations on which we base our understanding also have consequences. One study in the Eastern Cape, South Africa concluded that historical land use change was critical: particularly intense erosion was associated with cultivated land that had been abandoned and reverted to grazing Rowntree et al.
In a global review of ecosystem sensitivity to grazing by large herbivores, Milchunas and Lauenroth concluded that an evolutionary history involving grazing animals and the local environment was a critical factor in determining negative impacts of grazing on productivity. Establishing the extent of any particular desert is complicated by the use of localised names for areas within large deserts Middleton , but this paper follows Sternberg et al.
There are many reports in the literature indicating that desertification is a serious issue in the Gobi Fullen and Mitchell ; Yang et al. Among the causes, an increase in the number of domestic livestock is frequently cited as a major driver of degradation in Mongolia Sasaki et al. However, not all agree about the extent or severity of desertification in the Gobi or about the importance of the human impact.
In a review, Wang et al. Similarly, Khishigbayar et al. Assessments of rangeland condition and desertification also vary widely. Of course the UNCCD definition of desertification cited above means that rangeland degradation can be the result of both climatic variability and human activities e. Liu et al. However, some of the disagreements in the literature may also be the result, at least partly, of the methodology used. Khishigbayar et al. Yang et al. Despite the difficulties and disagreements surrounding our understanding of change in dryland landscapes, regions that are inherently variable in biophysical terms and prone to stochastic disturbances, there remains a prevalent view of desertification as being widespread and of overgrazing as a core cause in both Mongolia and China, a perspective that has informed policies.
The design of policy responses, particularly many of those applied to Chinese grasslands, incorporates a specific aim of reducing the generation of dust and sand storms. Under Pasture to Grassland, grazing on existing pastures is banned either permanently, for a few years, or seasonally in specific zones; Beijing—Tianjin Sand Source Control involves a mix of measures, including grazing prohibition or rotation or rest, and the conversion of cropland to forest or grassland though not for grazing.
Assessments of the efficacy of these projects in remediating desertification in general, and specifically in preventing dust storms, do not all agree. Tan and Li show that the GGW programme greatly improved vegetation cover, as measured by the normalised difference vegetation index NDVI , and effectively reduced dust storm intensity in northern China. A similar conclusion about vegetation is reached by Zhang et al.
After a decade-long fencing experiment to assess the impacts of a grazing ban on sandy rangelands in Inner Mongolia, Su et al. They conclude that some degree of grazing by livestock may provide critical ecosystem services by regulating woody plant encroachment.
Other researchers point to warmer temperatures and greater rainfall as being more important drivers of greening trends in northern China Piao et al. Qu et al. That said, Huang et al. Tree planting initiatives have also been promoted in Mongolia, where state-sponsored planting programmes date back at least to the s in many parts of the country, including forestry offices in the Gobi region Dorjsuren and Sainbayar A major new national initiative was launched in the Gobi in , when the government pledged considerable investment for a large-scale planting scheme designed to reduce dust storms and mitigate the impacts of desertification.
The scheme, variously known as the Great Green project or the Korea-Mongolia Greenbelt Project since planting sites are co-funded with Korean bilateral aid money , is intended to extend east—west across the country for km with a width of at least m.
A number of dust storm studies in the Gobi region point to rainfall and other climatic drivers of change as being of greatest importance. Lee and Sohn found that most dust source areas in China experienced a continuous decrease over a year data period — which they attribute to enhanced precipitation and its effects on soil moisture and surface vegetation.
Fan et al. Zhu et al. Lee and Sohn also conclude that an increase in dust occurrence after the mids over eastern Mongolia and Chinese Inner Mongolia may be largely influenced by drought conditions and associated soil moisture change, while Kurosaki et al.
Forty years of dust event data from Seoul in South Korea show an increasing trend from the early s Kim which is attributed to an eastward shift in the regional source of dust from Mongolia to Manchuria but also to changes in upper-level synoptic transport patterns.
Intensified atmospheric circulation and an associated increase in wind speed as well as changes in snow cover, soil moisture and potential evaporation rates throughout Inner Mongolia and Manchuria are considered to be the main causes of the increasing number of dusty days in Korea.
No mention is made of policies to control desertification or dust storms in any of these dust storm papers. The deserts and semideserts of China and Mongolia are well established as significant sources of desert dust, although on the global scale the most important regional source is not the Gobi but the Taklamakan Desert Goudie and Middleton , located further west in the Tarim Basin.
The regional preeminence of the Taklamakan is confirmed by many studies e. Shao and Wang ; Zhang et al. Several specific sources within the Gobi are also identified. Prominent among these are the Badain Jaran Zhang et al. The standing of rangelands in this picture remains unclear. There are many uncertainties and gaps in our knowledge about how grasslands may act as dust sources Shinoda et al. In a rare field experiment, Hoffmann et al. However, areas with significant livestock populations the lowlands of the eastern Mongolian Plateau, including Dornogovi province in Mongolia, and the Otindag and Horqin sandy lands of Inner Mongolia were identified by Zhang et al.
Zhang et al. These uncertainties are of course compounded by the doubts surrounding the overall extent and severity of desertification in the Gobi, the debate over the relative importance of biotic vs abiotic drivers of vegetation dynamics in rangelands, and the sustainability of pastoralism in general. All these factors are to some extent facets of different paradigms of rangeland ecology. Contemporary policies towards pastoralism in rural China have multiple objectives Addison and Greiner Generally, they aim is to improve both the environment and the livelihoods of pastoralists.
They are designed to address the former by restoring grassland ecology, combatting desertification and reducing dust storms, and the latter by supplementing the incomes of herders and encouraging them away from traditional forms of extensive pastoralism. Central facets of these mandatory schemes for pastoralists include a shift towards exclusive user rights enforced by fencing, prescribed carrying capacities per hectare where grazing is allowed, and grazing bans elsewhere, with cash payments to compensate pastoral households, or to incentivise herd sizes being kept below set stocking rates.
There is no doubt that these schemes are significantly altering the livelihoods of a great many pastoralists living in China and that a critical aspect of these changes is a trend towards less mobility. Ecological migration programmes have also affected pastoralists in other drylands in China, notably in Tibet where the goal is to move , herders off pastures to begin new lives in towns and cities Wang et al. Both Yeh and Wang et al. These high numbers in resulted in an average stocking rate of 4.
The results showed an increase of sparse and medium density shrublands mainly phryganic ecosystems at the expense of the dense ones, as well as of forests.
This evolution indicates degradation, since fewer shrubs suggest less woody cover to protect the soil and sustain productivity. The impact of overgrazing was more severe when it was combined with pastoral wildfires. Overgrazing is management oriented but as a process it is affected by several physical and socio-economic factors as well. Assessment indicators may relate to management, vegetation and abiotic conditions as well as to social, economic and political ones.
Overgrazing is caused when the number of animals carried in a rangeland are more than its grazing capacity, suggesting these extra animals could be from a few to too many. As a result, the number of animals grazing in a rangeland or the grazing intensity, expressed as stocking rate, is a very important indicator of rangeland degradation Papanastasis, ; Due to the different way that the various grazing animals collect the forage, their impact on vegetation is different Rook et al.
Also, the system with which animals graze in rangelands is important, too. For example, continuous grazing on a year-long basis is more adverse to species composition than a seasonal or rotational grazing system Sternberg et al. It has been already mentioned that combining overgrazing with wildfires can be more detrimental than either of the two processes alone. The distribution of available infrastructure may decide whether a rangeland will be evenly used or not; normally the animals tend to graze more intensively near the watering points and animal sheds than away from them Ghossoub, Finally, overgrazing will be avoided if alternative feed resources are available and therefore the production system applied is affecting the impact of grazing animals on rangelands Papanastasis, For vegetation, important indicators are the amount of biomass produced or left at the end of the grazing period, the plant cover Papanastasis et al.
Usually, when overgrazing has occurred, the pasture is filled with weeds, which are undesirable plant species to animals. Soil and climatic variables such as soil depth, slope gradient, parent material, soil erosion, rainfall amount and distribution , and temperature are all affecting vegetation and therefore the number of animals that can be grazed on a rangeland. There is a direct relationship between the soil depth Papanastasis, or the amount of surface rocks Alexandris et al.
Also, herbage production is very much affected by rainfall and air temperature Papanastasis, Considering socio-economic indicators, they may include EU subsidies for animal numbers, the local traditions as far as the flock size is concerned, the land tenure private, state or communal rangelands , the alternative income that the farmers can have apart form raising livestock and the laws that dictate the use of rangelands by the farmers. All these indicators interrelate with each other and with several physical indicators e.
Overgrazing is related ro other issues, particularly land abandonment and deforestation. Land abandonment Intensive irrigation Overgrazing Deforestation Littoralisation Agricultural practices Economic activity Land degradation Water resources Social structure Institutional organisation. DIS 4 ME. Working Paper. Nairobi, Kenya. Rangelands have environmental, social and economic benefits, including support to national economies through tourism and employment.
In Tanzania, tourism contributed 9. Despite their benefits, rangelands are under threat of continued degradation driven by anthropogenic and natural causes. Natural causes of rangeland degradation include climate change and variabilities, aridity and desertification, drought, as well as alien species invasion. Satellite photos revealed an area of privately-owned rangeland that was managed sustainably by the rotation of pastures for grazing.
Because the owner had a vested interest in maintaining the quality of the rangeland, he managed it with the future in mind. However, the public land that lay adjacent to his property had been overgrazed past its carrying capacity. The soil was compacted and invading plants unfit for grazing had taken over. As a consequence, large numbers of grazing animals died off, followed by many humans who depended on them for sustenance Hardin, Bogbit Chiras, D.
Natural Resource Conservation 10th ed.
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