13 ALPINE RANGELAND ECOSYSTEMS AND THEIR MANAGEMENT IN THE QINGHAI-TIBETAN PLATEAU by Long Ruijun^[15]

Overview

There are about 8.5 million sq km areas of alpine land at an elevation higher than 3 000 m above sea level distributed throughout the world, of which the single largest and the highest plateau is the Qinghai-Tibetan Plateau covering an area of nearly 2.5 million sq km. Thus, it is referred to as the "third pole" or "the roof of the world". Given the high altitude and extreme harsh environmental conditions, this high elevation grazing land ecosystem might, up to the present, be among the least affected by modern society. The alpine rangeland ecosystem of the Qinghai-Tibetan Plateau displays inherent characteristics that lead the system to being relatively stable. The alpine pastures have retained a certain level of productivity over thousands of years. It has also resulted in a weaker and slower response to some arguably advantageous management measures, and consequently they are very difficult to rehabilitate once destroyed. Temperature and moisture are thought to be two key factors that drive formation and development of the alpine rangelands. Heat (temperature) seems to play a predominant role in limiting growth and the reproductive pattern of alpine vegetation growth, while the annual rainfall mostly determines the distribution of ecozones of alpine rangelands.

In general, the yield of native alpine pastures is low and seasonal, thus leaving a feed gap between annual pasture provision and the requirements of the grazing animals. Since agricultural cultivation is not possible, continuous year-round extensive grazing - either transhumance grazing on the vast plain of the central Plateau, or seasonal rotation within certain mountain regions - is the land-use pattern throughout the Tibet-Qinghai Plateau. Thus, both livestock (including yak, Tibetan sheep and goats) and wildlife species largely depend on alpine pastures for survival. The alpine native forages have characteristically high protein, fat and sugar contents with relatively low fibre content compared with lowland plants. Another advantageous feature of these plants is that they contain a reasonable quantity of tannins, which potentially enhance the absorption of nitrogen by the host animal. The high quality of fresh alpine forages allow grazing yak and sheep to recover the bodyweight loss sustained over winter through compensatory growth during a short growing season of 90 - 120 days.

Although degradation of alpine rangeland has occurred over decades on the Plateau, it has become worse during the past decade due to a rapid increase in human and animal populations across the Plateau. This has led, in turn, to increasing demands on the alpine rangelands. A conventional seasonal rotation or transhumance system has been considered an effective way of avoiding the rangeland degradation.

However, the distance that herds can move has been restricted since the start of the "Household Responsibility System" in the 1980s, which was intended to encourage a semi-sedentary or completely sedentary lifestyle.

The nutrient resource of the soil pool is the most important basis for the growth and maintenance of the alpine vegetation. Any small change in this soil nutrient pool will have a profound effect on other components in the system.

The varied topography, altitudes and climate give rise to great diversity in alpine rangeland types. The rangelands include the lush, alpine meadows in the Himalayan mountains and eastern Tibetan Plateau, semi-arid scrublands of the dry valleys of central Tibet, the spacious alpine steppes of Tibet's northern plains and the cold, dry deserts of the Kunlun mountains. Therefore, no single management strategy can be applied to all the alpine rangeland types.

The Plateau's rangeland-livestock husbandry has lasted for centuries. Tibetan nomads acquired complex knowledge about the utilization and management of the alpine rangelands in which they lived and upon which the animals' survival depended. Serious degradation of alpine rangeland over the whole Plateau has brought a great threat to the alpine ecosystem and its nearby environment. Coping with these problems more effectively will require a clear understanding of the vast body of indigenous knowledge of the alpine rangeland ecosystem and herders' traditional experience. This is in order to work out sound utilization and management guidelines for the rangeland and ensure that herders get the best out of their pastures. This chapter aims to contribute to that understanding.

Background and present status

The alpine rangelands where yak can be found currently cover more than 2.5 million sq km of the Qinghai-Tibetan Plateau and its surrounding territories. As referred to in Chapter 1, these rangelands are at altitudes from 2 000 m to 5 000 m with a cold, semi-humid climate. They extend from the southern slopes of the Himalayas in the south to the Altai in the north and from the Pamir in the west to the Minshan mountains in the east. The alpine rangeland resource is vital for the livelihood of the people and their livestock raising. Much of this region offers an important habitat for many wildlife species, such as blue sheep (Pseudois nayaur), kiang or Asiatic wild ass (Equus kiang), Tibetan antelope (Pantholops hodgoni), black necked crane (Grus nigricollis) and the endangered snow leopard (Panthera uncia) (Miller and Craig, 1996; Richard, 2000). Apart from these, many areas are now designated as protected with a high potential for the development of tourism. The available alpine rangelands of the Plateau cover about 128.2 million ha, or approximately 30.7 percent of China's total area of rangelands (Bureau of Animal Husbandry and Veterinary Medicine, Ministry of Agriculture, China, 1994).

These alpine rangelands consist mainly of alpine steppe (including alpine meadow steppe and alpine desert steppe), alpine desert and alpine meadow (Table13.1). Due to the high altitude and harsh environment, agricultural cultivation is not possible on most alpine plateaux. The only way the land can be used is for livestock grazing (Goldstein et al., 1990). Therefore, ruminant (yak and Tibetan sheep) farming plays the most important role in the socio-economic and environmental systems of the Plateau. These rangelands, especially the verdant pastures of the eastern Plateau, offer great reserves of forage for grazing livestock, the products of which account for a significant percentage of the gross national product (GNP) of these areas (Wu, 1997).

Table 13.1 Types of available alpine rangeland on the Qinghai-Tibetan Plateau and their theoretical carrying capacity in 1994 [Source: Bureau of Animal Husbandry and Veterinary Medicine, Ministry of Agriculture, China, 1994]

Thirteen million yak and 41.5 million sheep (Long, et al, 1999a) as well as large numbers of wildlife raised on the Plateau support a human population of 9.8 million. These animals are either largely (livestock) or totally (wild herbivores) dependent on the native alpine rangelands for their survival (Long et al., 1999a,b). Consequently, competition for feed between domestic and wild animals is inevitable in areas where they overlap. Continuous year-round extensive grazing (either transhumance grazing on the vast plain of the central Plateau or seasonal rotation within certain mountain regions) is a unique land-use pattern on the Qinghai-Tibetan Plateau. This form of utilization differs from other alpine rangeland ecosystems in the world where the pastures are only grazed by livestock in the summer season. Until the 1950s, a transhumance pastoral system was the main grazing pattern in most of the plateau areas, the distance travelled by herds being dependent on forage availability and quality.

Thus, the distances covered by herders could vary from tens to hundreds of kilometres, or even more, according to the particular rangeland productivity of that area. Pastoral mobility was probably the simplest and the most effective way of optimizing the use of alpine rangeland resources without harming the ecosystem, but only if the rangeland resources were sufficiently abundant to allow the livestock free access, both in space and across time.

From the 1960s to the 1970s, most of the pastoral communities living in the eastern (Sichuan and Gansu) and northern (Qinghai) parts of the Plateau have changed from a migratory lifestyle to semi-sedentary or completely sedentary grazing practices.

However, these changes are still a relatively new phenomenon within Tibetan territory, associated as they are with the Household Responsibility System policy that was implemented in China from the beginning of the 1980s (see Chapter 12). Under this system, communal livestock were divided among every family, based on family numbers, and consequently, some of the pastures used during cold season (the so-called winter-pastures near by the herders' sedentary houses) were also allocated to herders individually in yak-raising areas. The rest of the rangelands are normally situated in remote or alpine mountainous areas grazed mainly during the warm season (the so-called summer pastures). These still belong to the State or are used as communal lands and so engender less concern for graziers than the winter pastures. Of course, the Household Responsibility System is intended to benefit most herdsmen and help raise their income through culling out more livestock, improving animal husbandry and managing their rangelands in a sustainable way. But such changes from a long-ranging and highly mobile yak-herding system in the past to a short-ranging and sedentary lifestyle also carry some potential risks for the alpine rangeland ecosystem since the rangelands of the Qinghai-Tibetan Plateau are more than just a resource to sustain livestock. They form the headwaters of the six major river systems of Asia - in particular, the Yellow River is regarded as the "Mother river", and the Yangtse being the "life river" of Chinese nationality. Their diverse ecosystems of forest-alpine ecozones, shrub alpine meadows and range alpine meadows lead to extensive quantities of water being held underground and regarded as the "underground reservoirs" of the Plateau and also called the Chinese "water tower".

The Plateau, as a natural protective screen for China in its southwest, plays a tremendous role in driving and regulating climate of western and southwestern China, even the northern hemisphere. In the past two decades, animal numbers have increased rapidly. This has, in turn, aggravated grazing pressures and accelerated the rangeland degradation (Table 13.2). This degradation is now one of the most serious environmental and socio-economic issues in the Qinghai-Tibetan Plateau region accounting for 32.1 million ha and 42.5 million ha in the 1980s and 1990s, respectively. In Qinghai, the headwater areas, where the Yangtse and Yellow rivers have their source, are particularly affected. Some pastures have degraded so badly that "black patch" land has formed (i.e. rangelands with a high density of black soil patches) from which most perennial vegetation has disappeared and been replaced by annual grasses or forbs, which are normally consumed completely by animals at some times of the year. These degraded rangelands with black, denuded soil covered 3.79 million ha and 7.03 million ha of alpine rangeland in the 1980s and 1990s, respectively.

Table 13.2 Areas and distribution of degraded rangelands on the Qinghai-Tibetan Plateau [Source: after Long and Ma, 1997] (unit ha x 10 000)

Ma Yushou et al. (1998) reported that in Dari county of Qinghai province, grassland converted to "black patch" due to overgrazing, extended from 0.17 million ha in 1985 to 0.58 million ha in 1994 - an annual increase of 14.7 percent. In these areas, herbage production is only 13.2 percent of that on the non-degraded grassland, and herbage cover is less than 30 percent. Inedible and poisonous grasses accounted for up to 76 percent of the sward.

Thus, rangeland degradation is often manifested by decreased diversity of plant species, reduced sward height and vegetation cover, increased undesirable and unpalatable grass species and even the occurrence of toxic species harmful to animals. Above all, there is a sharp reduction of acceptable biomass production. If the vegetation density is insufficient to cover the ground surface, wind erosion and desertification take place. In general, the alpine rangelands of the Qinghai-Tibetan Plateau are suffering degradation, soil wind erosion and desertification. These problems make the sustainable management and utilization of the rangeland resources more difficult and, in addition, make the alpine ecosystem even more fragile and unstable than before. Overall, overgrazing is recognized as the most fundamental cause of the degradation.

Climate

Air and solar radiation

The average depth of the atmospheric layer above the alpine rangeland of the Qinghai-Tibetan Plateau is about two thirds of that in the coastal areas. The atmospheric pressure and density are only about 50 - 60 percent and 60 - 70 percent, respectively, of those at sea level. These features, together with a smaller proportion of moisture and dust in the air, lead to much short-wave light of blue and particularly ultraviolet passing through the atmosphere that can then be absorbed by the green leaf material of the alpine vegetation. Annual sunshine is between 2 000 and 3 600 hours and the value of solar radiation varies from 5 000 to 8 000 MJ sq m per year, compared with only 2 000 to 3 000 MJ sq m per year in the eastern lowland area of China at the same latitudes. Hu et al. (1988a) calculated the annual energy conversion efficiencies from total solar radiation and physiological radiation to above-ground biomass energy in sedges (Kobresia capillifolia) meadow as 0.11 percent and 0.22 percent respectively, while it reached 0.40 percent for physiological radiation during the growth period. These figures are relatively low compared with corresponding values of 0.16 percent, 0.32 percent and 0.69 percent found in forbs (Polygonum viviparum) meadows in the same region (Hu et al., 1988b). Physiologically, high solar radiation associated with high density of short-wave light has a profound effect on plant development: It limits cell elongation and thus reduces vegetative growth and forces cell division to accelerate reproductive development. Consequently, compact, stubbed and even cushion plant forms appear above ground while a well-developed root system is formed in the topsoil layer.

Temperature

The average annual air temperature is generally below 0°C, while the average temperature in January drops below -10°C. The average in the hottest month (July) does not exceed 13°C (Table 13.3). In meteorological terms, an absolutely frost-free season does not exist on the Plateau. The growing season of native plants varies from 90 to 120 days, but periods of relatively vigorous plant growth are even shorter than that. Temperature differs between day and night by 12° - 17°C, which is propitious for the accumulation of nutrients assimilated. Zhang and Ma (1982) reported that assimilation lost through respiration at night in alpine plants is only equal to about one third of that produced by photosynthesis during the day. Thus, alpine vegetation characteristically has relatively high levels of nutrients in the form of crude protein, fat and sugar (nitrogen-free extract), and a low fibre content compared with that of lowland and tropical pastures. These compositional characteristics also help native plants resist cold weather and other harsh environmental conditions.

Rainfall and wind

Drought is another feature of the plateau climate. More than 65 percent of the area receives less than 300 mm rainfall per year; the rest has an annual rainfall not exceeding 500 mm.

With the rainfall decreasing from southeast to northwest, the alpine rangelands display a diverse assortment of plant communities, including three dominant rangeland types: alpine meadow, alpine steppe and alpine desert (Table 13.1). Alpine shrub meadow appears if rainfall is sufficient on the north slopes of mountains.

Table 13.3 Climatic characteristics of typical regions on the Qinghai-Tibetan Plateau [Source: adapted from Hu, 2000]

¹Above sea level; ²annual average temperatures; ³average temperature in January; ⁴average temperature in July; ⁵differences in temperature between day and night; ⁶annual cumulative temperature above 0°C; ⁷annual rainfall; ⁸annual sunshine hours.

Disasters from hailstorms occur frequently in summer and from snowstorms in the spring. Strong winds occur throughout the late winter and spring seasons, with a mean wind velocity of 3 - 4 m s^-1, even reaching over 5 m s^-1 in spring. Such winds can blow away about one third of the yield of standing vegetation from winter-spring pastures.

Effect of climate on alpine rangeland formation and evolution

Climate plays the most active and effective role on rangeland formation and evolution. In terms of alpine rangeland, water and heat (temperature) have more profound effects on its formation and development than any other indigenous factor, such as soil and topography. The summer temperature of the whole troposphere above the Plateau is higher than that of surrounding regions (at the same elevation). Moreover, with stronger solar radiation to the Plateau and the low level of moisture in the air, low heat loss through evaporation is yet another feature of the Plateau's climate. Thus, the distributional upper limits of rangeland types are much higher on the Plateau than on solitary or smaller mountains (Chang, 1981). A moisture gradient from humid and subhumid to semi-arid and arid, from southeast to northwest, results in a corresponding series of diverse rangeland ecozones on the Plateau.

In the western part where rainfall is only about 50 mm annually, the vegetation is of suffrutescent desert and desert-steppe types composed mainly of Ceratoides latens. In the northwestern part, the climate is very dry and cold by reason of high altitude and the more northerly latitude, and so a sparse alpine desert of low suffrutescent and cushion-like Ceratoides compacta has developed there. On the vast flat lands of the central Plateau, the annual precipitation increases to about 200 mm, and alpine steppe vegetation of Stipa species prevails. In the eastern part of the Plateau there is a cold, low-pressure zone where annual precipitation normally reaches up to 600 mm. With this cold and wet climate, a special kind of alpine meadow has developed, which represents the main body of alpine rangelands. This meadow consists of sedge species and low scrub, such as Salix and Rhododendron species. This series of alpine vegetation ecosystems, from southeast to northwest, was formed and developed in the Quaternary period (Chang, 1983). Even now, the three main kinds of pastures are still the most common rangeland types in the Plateau (Table 13.1) on which more than 800 forage species are growing. Among them, the two genera of Carex and Kobresia (grass-like plants having achenes and solid stems, which belong to the Cyperaceae family) are by far the most important indigenous plants. This is not only because of their high biomass production, early "green-up", wide distribution and good resistance to extreme climatic conditions, but also due to an incredibly high grazing tolerance.

Grasses such as Stipa and Poa species comprise a large proportion of the alpine-steppe sward. Forbs, i.e. broad-leaf herbaceous plants, are companion species in the alpine meadow swards or interspersing plants in the alpine desert.

Vegetation characterization

Patterns of production and growth

In general, temperature is the single most important factor determining the distribution, diversity, growth rate and biomass production of alpine vegetation. Fortunately, during the short growing season, warmth coincides with water supply (rainfall). These, as already mentioned, are the most fundamental factors supporting the primary productivity of the alpine rangeland ecosystems. Productivity ranges from 1 to 4.5 tonnes DM per ha per year. Thus, a high-efficiency and unique vegetation growth pattern is formed within the ecosystem.

Three distinct phases of biomass availability to the animals can be identified: Phase I has a surplus of green forage (June - September); Phase II has a relative surplus of more mature and dry forage (October - January) and Phase III has a shortage of dry forage (February - May). Based on seasonal growth, phenological and climatic aspects, the points concerning the growth pattern of alpine herbage can be summarized as follows:

Growth

Green-up (after winter) starts relatively late but growing activity ends early. Consequently, the growth season of the native vegetation lasts for only 90 - 120 days from May to August or September (Long et al., 1999a) as shown in Figure 13.1. The first (July) and second (September) peaks of biomass production are the result of a faster growth of sedges after green-up till July, and then grasses take over.

Figure 13.1 Biomass production in alpine meadow in the Qinghai-Tibetan Plateau

In view of this short growing period, the alpine plants, particularly the sedge species, have evolved strong tiller extensibility, since their seeds have poor germination. In order to finish the growth cycle (from germination to seed formation) within a short period, sedge has developed clonal or asexual ways to continue its regeneration.

Accumulation of above-ground biomass

Within the growing season, fresh biomass accumulates quickly but the maximum yield of dry matter does not appear until vegetation growth is finished. Nu Xindai (personal communication, 2002) indicated that Kobresia littledalei, a sedge species distributed in Dangxong valley, Tibet, showed a rapid absolute mean growth rate (expressed as DM g m^-2 per day) of 1.1 from green-up to 15 May, 1.9 from 16 May to 15 June, and thereafter reached 2.8 from 16 June to 15 July from 1983 to 1985. Hu et al. (1988b) found that the biggest absolute growth rate (5.8 DM g m^-2 per day) appeared one month after the green-up in forb (Polygonum viviparum) meadow, while its net primary productivity above ground was 481.1 DM g m^-2 per year. This is higher than the value of 340.1 found in sedge (Kobresia capillifolia) meadow in the same part of the eastern Qilian mountain. Due to low temperatures, sedge and grass species are normally not able to generate tillers to contribute to the final biomass production in autumn.

Storage of dry biomass

Wilted herbage remaining on the rangeland from the summer's growth is available to the animals from autumn to winter. Owing to livestock trampling and grazing on the stand, a proportion of stems and leaves fall off the plants to form herbage fractions in the stand. If not consumed timeously, this biomass is liable to be lost by wind or snowstorms during spring. The proportion lost probably reaches up to 30 percent of total biomass yield per year from winter stands.

Defoliation and decomposition

Due to above-ground biomass production being generally low, there is less accumulation of the fallen herbage fractions. While the proportion decomposing varies from 51 to 63 percent annually during the warm season, the decomposition is suppressed to a large extent by relatively low temperatures. Consequently, the senescent herbage is removed by soil fauna mainly between July and September. Other factors, such as grazing activity, may reduce the rate of decomposition; in contrast, improving soil moisture and fertility would lead to enhancing of the degradability of these materials (Li et al., 1982). A lower cellulose decomposition rate occurs where animal access is blocked or the meadows are under-grazed. This results in a considerable amount of the residual herbage mass being left in some areas, particularly under shrubs. In turn, this may reduce the forage growth and yield because the increased amount of dead material relative to vegetative growth creates shading by dead material, and thus reduces photosynthetic capacity.

Absence of legume species

In alpine vegetation communities there is a characteristic lack of forage legume species that, in turn, leads to an insufficiency of forage protein for livestock during the cold season. Moreover, legumes are difficult to establish in the Plateau due to its cold weather. No perennial forage legume has been developed as yet that is well adapted to the Plateau's weather. However, single or mixed grass communities can be easily established by proper selection of adapted grass species for the relatively lower land areas (around 3 000 m a.s.l.).

Accumulation of underground biomass

The underground biomass production is generally higher than that above ground, irrespective of the type of alpine rangeland. The average total underground biomass of different alpine vegetation meadows varies from a lowest of 627 g m^-2 (Elymus nutans meadow) to the highest of 12 827 g m^-2 (Carex spp. meadow). Other types include Kobresia humilis meadow (1 265 g m^-2), (Polygonum viviparum) meadow (5 702 g m^-2) and Dasiphora fruticosa (shrub) meadow (6 014 g m^-2) (Hu et al., 1988b). It is estimated that about 65 percent of total underground biomass is distributed between the surface and 10 cm down in the soil layer. The live root yield accounts for about two thirds of the total underground biomass. Due to the decomposition rate of dead root and fallen herbage lagging behind their accumulation in alpine rangelands, a large quantity of organic matter is preserved in the soil, the proportion varying - depending on soil type - from 0.49 percent in alpine desert soil to 15.7 percent in subalpine meadow soil (Table 13.4) (Xiong and Li, 1987).

Nutritive value of alpine vegetation

The quality of alpine rangelands is influenced by management, environment and plant species. Attaining the optimum stage of growth at grazing is recognized as the most significant management factor, due to the negative relationship between vegetation maturity and forage quality. (The map of the Qinghai-Tibetan Plateau in the Appendix shows most of the locations referred to in subsequent sections of this chapter).

Table 13.4 Variation in organic matter (OM) and total nitrogen (N) contents of alpine soil types to a of 10 cm [Source: adapted from: Xiong and Li, 1987]

Chemical composition profile

Sedges, as the fundamental species of many types of alpine sward, are generally components of pasture along with grasses and forbs. Sedge, grass and forb species differ in chemical composition as shown in Table 13.5, and so, their contribution to the pasture composition will also affect forage quality. For example, crude protein (CP) contents of sedge and grass species range from 6 to 16 percent on a dry matter basis - relatively lower than for forbs, which vary from 12 to 22 percent. It seems also that there is no significant variation in contents of crude fat (CF) (about 4 percent) and nitrogen-free extract (NFE) (45 - 50 percent) when samples are harvested during the flowering stage in July. Zhou and Simon (1995) reported similar results for CP content in Sunlian (the southern part of the Plateau) and in Hongyuan (northwestern Sichuan). Long et al. (1999a) also indicated that for Tibetan forages, increasing age at harvesting led to a significant decrease in nitrogen (N) content and an increase in neutral detergent fibre (NDF) content of both forbs and shrubs. Nitrogen content in sedges and forbs tended to be greater than that in grasses.

Intake, acceptability and dry matter digestibility

Feeding value of pasture depends on acceptability, dry-matter intake, forage digestibility and the efficiency of utilization of the end products of rumen digestion. On the grazing systems of the Tibetan Plateau, forage intake is largely influenced by pasture availability.

It may reach 4 - 5 kg DM per day for adult yak in summer and autumn, and be reduced to 1 - 1.5 kg DM per day, or even less, during late winter and early spring. Consequently, the animal's live weight varies much among seasons. On the summer pastures, acceptability and digestibility of forages become perhaps the major factors affecting the intake by the animals. Several observations (Ren and Jin, 1956; Zhou, 1984; Zhou and Simon, 1995; Long Ruijun, Hu Z.Z. and Xu Changli, unpublished data 1999) showed that sedges and grasses have a better acceptability than other species. On the basis of these studies it can be estimated that the proportions of the different kinds of forage plants in daily grazing diets in summer were sedges: 30 - 50 percent, grasses: 20 - 50 percent, forbs: 16 - 20 percent and legumes 1 - 3 percent. Cincotta et al. (1991) indicated that the proportion of sedge species accounted for 64.1 and 38.4 percent of the diet of yak and sheep, respectively on summer pastures of the Changtan area. Comparison among alpine forages harvested in August, September and October indicated that forbs had the highest 48-hour in sacco dry matter degradability, followed by sedge, grass and shrub. Figure 13.2 illustrates profiles of the 48-hour in sacco dry matter degradability from monthly samples of three different types of native swards that form the main body of alpine meadow on the Plateau. Although the dominant species varied from type to type and thus affected sward state (sward height, structure and mass), the trends in terms of the in sacco dry matter degradability are quite similar (Table 13.6). Obviously, the rates of dry matter degradability for all sward types in general are greater than 50 percent, but a big variation exists between different months throughout a year.

Figure 13.2 The 48-hour in sacco DM degradability of natural pasture samples

Table 13.5 Chemical composition of alpine plants cut at the end of July (unit: % DM basis) [Source: adapted from Long et al. 1999a]

Phenolics-related compounds

Ulyatt (1981) suggested that an "ideal" forage would have high protein content, high levels of soluble carbohydrate, some feature such as presence of tannins (that would either slow the release of soluble protein or render it less soluble in the rumen) and concentrations of minerals sufficient to maintain animal health. In most alpine sedge, forb and shrub species, the presence of microbial inhibitory compounds, or phenolics, have been revealed recently (Long et al. 1999a). Some of these inhibitory compounds were lately confirmed as being a phenolic-related compound of tannins (Long Ruijun, Hu Z.Z. and Xu Changli, unpublished data, 1999). Figure 13.3 illustrates that an appreciable quantity of tannins in a mixed alpine sward will potentially improve the forage-feeding value. The tannins protect the protein from degradation, thus providing a quantitative saving of nitrogen in the rumen and, further, allowing the bypass protein to be effectively used by the host animal in its small intestine. With a high value in fresh alpine forages, it makes grazing yak and sheep able to recover their previous bodyweight loss through sufficient compensatory growth during the short growing season.

Figure 13.3 Concentration of TECTa from natural pasture samples taken monthly

Table 13.6 In sacco dry matter degradability (I.S.D.) of some Tibetan forages at different stages of maturity [Source: adapted from Long et al., 1999a]

Types of alpine rangeland

Alpine meadow

Alpine meadow, also referred to as "Tibetan high-cold meadow", accounts for 49.3 percent of the total available alpine rangeland areas on the Qinghai-Tibetan Plateau. These vast grazing lands, distributed mainly in the eastern and southern parts of the Plateau, extend from 27° to 39° north latitudes and from 82° to 103° east longitudes. Due to the greater rainfall on alpine meadows than on alpine steppes and deserts, its primary productivity, in terms of biomass production and diversity of vegetation, is much higher as well. The vegetation on alpine meadow contains sedge species that include Kobresia pygmaea, K. microglochin, K. humilis, K. bellardii, K. capillifolia, K. royleana, K. tibetica, K. setchwanensis, K. kansuensis, Carex moorcroftii, C. prewalskii, C. scabrirostris, C. ivanoviae and Blymus sinocompresus; grass species that include Elymus nutans, Stipa and Festuca; forb species include Polygonum viviparum, P. sphaerostachyum, Potentilla anserina and Artemisia frigida; and shrub species that include Hippophae thibetana, Lonicera tibetica, Dasiphora fruticosa and Salix. Following the uneven annual rainfall and changing elevation, forage yield of alpine meadows with a ground-cover canopy of 80 - 100 percent varies widely, from a low of 1 500 kg DM per ha in eastern Tibet to a high of 4 000 kg DM per ha in southwestern Sichuan. As shown in Table 13.1, the alpine meadows have the highest theoretical carrying capacity of 0.91 sheep unit per ha per year, so that 63.2 million ha of alpine meadows may be expected to support at least 57.5 million sheep units. At present, about 8.5 million yak (60.7 percent of total yak on the Plateau) are raised on alpine meadows, which is equivalent to 34 million sheep units (1 yak = 4 sheep units). Between 15 million and 20 million Tibetan sheep are also grazing these alpine meadows. Although the real carrying capacity of the meadows seems close to theoretical capacity, overgrazing and degradation of meadows are developing extensively on the Plateau.

Alpine steppe

Alpine steppe is widely distributed in the centre of the Qinghai-Tibetan Plateau and on most of the southward-facing slopes of the mountains with a total area of about 55.5 million ha, accounting for 44.9 percent of the Plateau's total available rangelands. Water shortages lead to poor vegetation diversity and an open canopy ranging from 40 to 70 percent ground cover. In consequence, its yield varies from 350 kg to 1 000 kg DM per ha per year. Its community consists of grasses and sedges, such as Stipa purpurea, S. glareosa, S.capillacea, S. bungeana, S. breviflora, S. krylovii, S. aliena, Festuca ovina, Poa annua, Kobresia parva, K. tibetica, Carex scabriolia and C. trofusca. As suggested in Table 13.1, the theoretical carrying capacities on alpine steppe is 0.23 sheep units per ha per year. The largest proportion of livestock raised is sheep, followed by goats and then yak.

Alpine desert

The alpine desert lies mainly in the western and northwestern flat parts of the Plateau and on some upper areas of the high-altitude mountains. Extremes of dry or of cold can each form the alpine desert. This rangeland accounts for 5.8 percent of the Plateau, with the simple vegetation consisting mostly of Ceratoides latens, C. compacta, Ajania fruticulosa, Christolea crassifolia, Stipa glareosa, and Carex moorcroftii. The canopy ground cover reaches down as low as 20 percent and the yield of the sward is very low, varying from 100 kg to 300 kg DM per ha per year. About 12.5 ha are needed to sustain one sheep unit (equivalent to 0.08 sheep units per ha). Compared to alpine meadow and alpine steppe, the desert has less importance and receives less attention in terms of rangeland and livestock management, and goats are the dominant livestock. Some areas, so far with little human activity, are given protection by inclusion in "the national nature-protecting areas" in order to conserve wild animals, such as Tibetan antelope (Antilope), wild yak (Bos mutus or Poephagus mutus) and wild ass (Equus hemionus).

Alpine soil type and its characterization

Soil plays the most fundamental role in sustaining the alpine rangeland ecosystem, upon which diverse rangeland communities are established. As a deposited pool, wherein the nutrient transformation and energy flow of the ecosystem take place, it is also a habitat for soil micro-organisms and various animals. Nowadays, most measures to improve alpine rangeland productivity are achieved through amelioration of the condition of the soil pool. A given soil type is always associated with the vegetation community on it and, in the main, there are four different soil types in the Qinghai-Tibetan Plateau, namely that of: alpine meadow (including subalpine meadow, alpine scrubby meadow, subalpine scrubby meadow, peat-bog and peat), alpine steppe (including subalpine steppe), alpine desert (including subalpine desert) and alpine frigid soil. Table 13.4 summarizes the profile of chemical properties of these soil types and shows that the organic matter (OM) and total nitrogen (N) contents of alpine meadow soil types are much greater than those of other soil types. Similarly, the trend is for the amount of forage produced to increase with the OM and N content of the soil.

Soil micro-organisms are the other important component concerned in the status of alpine rangeland. The ecosystem and the activities of the micro-organisms have a profound effect on soil fertility and consequently impact plant growth and pasture production. Zhu et al. (1982) indicated that in the alpine meadow ecosystem of eastern Qilian mountain (3 200 m a.s.l.), the population of micro-organisms varies seasonally, being also affected by different soil and vegetation types. The highest numbers of micro-organisms in alpine meadow soil occur in the period from mid-July to mid-September but tend to decline after late October.

The soil mainly covered with forbs tends to have the largest number of bacteria, sedge (Kobresia humilis) meadow has the highest actinomycete population and shrub (Potentilla fruticosa) meadow has the greatest population of fungi and oligonitrophiles. In the soil of swamp meadow, the cellulose-decomposing micro-organisms are absent.

Zang J.X. et al. (1991) investigated the quantity and distribution of trace elements in the alpine meadow ecosystem, eastern Qilian mountain. The results showed that the alpine meadow soil (air-dried sample) is rich in trace elements, with contents as follows: Fe 36 000 ppm, Mn 652 ppm, F 594 ppm, Zn 127 ppm, Cu 28 ppm and Se 0.23 ppm. There is a view that the Se content is inadequate; however, no plant or animal deficiency symptoms appear to have been reported to date. Significant differences existed among soil types in the concentrations of these elements.

Utilization and management of alpine rangelands

Grazing utilization systems

The zone distribution of alpine rangeland types from southeast to northwest on the Plateau leads generally to a corresponding zoning of livestock production systems. Yak are mainly distributed on alpine meadows and higher proportions of Tibetan sheep are found on alpine steppes, while goats and Tibetan sheep mainly inhabit the alpine deserts. Therefore, there are a variety of different management strategies in use on the Plateau. The pasture itself, whether owned by a family or by a group of herders or a village, can be broadly divided into four seasonal rotation grazing systems according to (i) weather, (ii) landforms, (iii) rangeland availability and productivity and (iv) tradition. The use of different pastures at different seasons and the periodic movement of the animals to new grazing sites is part of the tradition of the herdsmen and finds its counterpart in some of the elements of "modern" rotational grazing systems for which "scientific" justifications have been produced (cf. Chapter 8).

(I) Two-season rotation system

This rotation system involves the summer-autumn pasture used in the warm season and the winter-spring pasture used in the cold season (Table 13.7). The summer-autumn grazing generally occurs some time between June and November and may last 140 - 170 days. The herd then moves to the winter-spring pastures for about 192 - 225 days from November (sometimes sooner) to May - the larger part of the year. In general, the two-season rotation system is used mainly in the wide Plateau areas. During the warm season, a yak herd may be moved every 30 - 40 days, depending on the state of the sward and the size of the herd. The distance between campsites varies from 20 to 40 km.

(II) Three-season system (A)

This rotation system is characterized by summer-pasture, winter-pasture and autumn-spring-pasture (Table 13.8).

Table 13.7 The pattern of utilization on the two-season rotation system (I) of the summer-autumn and winter-spring pastures

Table 13.8 The pattern of utilization on the three-season rotation system (II) of the summer, autumn-spring and winter pastures

In a system carried out in the northern piedmonts of the Himalayas, animals remain on both the summer and the winter pastures for about three months each. Livestock graze the autumn-spring pastures twice - once from the beginning of September to the beginning of December and then from March to May. Three-season rotation-grazing systems are commonly found in mountainous regions. In these systems, the herders rarely move during the summer to find different sites and only move when the season ends.

(III) Three-season rotation system (B)

This rotation involves a summer pasture, an autumn pasture and a winter-spring pasture (Table 13.9). The autumn pasture is used in this system for more than two months (61 - 81 days). The activities of the animals on the summer and winter-spring pastures are as for the two systems previously described.

(IV) Three-season rotation system (C)

This rotation involves a summer-autumn pasture, a winter pasture and a spring pasture (Table 13.10). In this system, the spring pasture is separated either from the autumn-spring or from the winter-spring pastures. The livestock remain on it for two to three months. Its rangeland types are mainly alpine riverside meadows or shrub lands. The grazing features of the summer-autumn and the winter pastures are as previously described.

Management of the seasonal pastures

Winter and winter-spring pastures

The winter and winter-spring pastures are normally located on relatively flat meadows, such as riverbank mesas, wide valleys and piedmonts, or south-facing slopes at lower elevations, where pastures have the highest forage output and the best acceptability relative to the other types of pasture. Therefore, these pastures, and particularly the winter pastures, are fenced mainly in order to accumulate the biomass for grazing in winter and spring. Accumulating standing dry forages on the winter and winter-spring pastures is the traditional way of supplying feed for animals during the cold season, as the plants on the Plateau are too short to cut for making hay. This management pattern results in a large proportion of the forage nutrients being wasted and, in consequence, feeding value is much reduced from that of the original green biomass when it was set aside, while a large quantity of above-ground biomass is lost, as discussed earlier. The condition of these pastures has a profound effect on the Plateau's rangeland-livestock production systems, particularly in the provision of feed for the larger herds. Therefore, because calving and lambing takes place on them, herders pay much attention to these pastures and use some improvement practices such as fertilization, flood irrigation, toxic plant removal and rat control. Such measures are usually applied along with enclosures formed with barbed-wire fencing.

Table 13.9 The pattern of utilization on the three-rotation system (III) of the summer, autumn and winter-spring pastures

Table 13.10 The pattern of utilization on the three-season rotation system (IV) of the winter, spring and summer-autumn pastures

Summer and summer-autumn pastures

The summer and summer-autumn pastures are generally located either at the higher altitudes, often on the north facing slopes of the terrain or on the relatively flat rangelands furthest from the settled homes of the herdsmen and their families. Most of these pastures are difficult to access or may even be inaccessible except in the warm season as they may become blocked during harsh weather or by poor road conditions. In early summer each year, usually in May but depending on the particular location, the herd may still be grazing the spring, spring-autumn or winter-spring pastures. As soon as the season allows, the herd is taken to the summer pastures. Because these pastures are usually far away from the winter or spring pastures, the herdsmen and their herds may need to travel several days to reach their new campsites. The summer pastures, free from fencing, are usually utilized as communal lands for a group of families or an entire village. Hence, there is free access for the herds, and the herders are accustomed to establishing their campsites at the same places every year. Only when the yield of the summer pasture cannot meet the animals' requirements, because of drought or rangeland degradation, do the herders have to move away. These pastures are effectively managed in the long term through extensive, paper-free agreements among the families of a village. Such agreements are made by three to ten families, or occasionally more, sharing the grazing of the same summer pasture (see Chapter 12). Breeding of the stock occurs on the summer pastures, and so the calving rate is largely dependent on forage quantity and quality of these pastures.

Spring and autumn-spring pasture

The spring and autumn-spring pastures are normally located near the winter pastures and the herders' houses, or they may be situated between the winter and summer pastures. Whether or not these pastures are fenced depends on whether or not they are owned by the herders. Before vegetation turns green in spring, both the quantity and quality of the forage remaining on these pastures are at their lowest for the year. The intake by the animals can be as little as one third of the amount consumed in the autumn. As a result, as much as a third of the live weight the animal achieved in the previous autumn is lost during the late winter to early spring period (before green-up) (cf. Chapter 6). This, in turn, leads to a large number of livestock in the herd becoming sick or weak - the so-called phenomenon of "spring sickness". Some of the sickest or weakest animals may die, especially if heavy snowstorms occur in the absence of sufficient feed supplementation and at the very time when most new calves and lambs are born.

Autumn pasture

The autumn-pasture, which may or may not be fenced, is generally located between the winter and summer pastures and usually closer to the winter pastures. By the end of autumn, the animals have achieved their maximum live weight. Autumn is, therefore, the best season for culling surplus stock.

Critical grazing periods

From the point of view of pasture management on the Plateau, the two critical grazing periods are the approximate two-week periods of early spring immediately after green-up and of the late autumn, before the end of vegetation growth. Grazing activity just after green-up will lead to most growing points of plants being eaten by animals, which is, in turn, harmful to tillering and the ability of plants to re-grow. Areas of the sward that are overgrazed prior to the decline in plant growth in the autumn reduce the storage of nutrients in the root system and will therefore have poorer green-up the following spring. This will lead to less seed being produced for the soil-seed bank. The overall consequences are rangeland degradation.

In practice, it is difficult to avoid the problems associated with the two critical grazing periods unless sufficient supplementary feed can be provided in the early spring or alternative land found for grazing in the late autumn. A traditional approach, developed by herdsmen to avoid or alleviate the above situations, is to have a two- to three-year rotation (crossing-over) system between part of the winter or autumn pastures and the spring pastures. The early spring, as mentioned earlier, is also the critical period for the survival of the animals. Therefore, a sound management of the spring pasture and of the herd grazing will have a large influence on the sustainability of the Plateau's rangeland-livestock production systems. To achieve this, herders, policy-makers and researchers need to reach better mutual understanding and then work together.

The potential for improvement of the alpine rangeland

Irrigation

Flood irrigation is perhaps the most common and economic method used by herders to improve the native rangelands, whenever water is available and easily applied. Due to variation of the landforms, not many pastures can be irrigated by running water. Irrigation is applied mostly on areas of winter or autumn pastures that lie on flat areas of riverside and on open lands down-stream that allow easy flooding. Long Ruijun, Hu Z.Z. and Xu Changli (unpublished data) showed that a sedge-grass meadow developed under an annual mean rainfall of 414 mm and mean temperature of minus 0.1C° responded dramatically to irrigation. Five similar pieces of meadow, each 1.5 - 2 ha in size, were flooded thrice (with an equal amount of water each time) in June. Increasing the quantities of total extra water from zero to 0.45, 1.35, 1.80 to 2.25 tonnes per ha, led to corresponding increases in aerial biomass production with these five treatments. The increases were 1.28 to 3.56, 3.15, 5.38 to 4.79 tonnes per ha, respectively. The response of sedge, grass and forbs to irrigation varied depending on the quantity of applied water. Forbs were more responsive than sedges and grasses when 0.45 tonnes per ha of water was introduced; with 1.80 tonnes per ha water, sedges showed a greater response than forbs and grasses, while grasses were the most responsive when 2.25 tonnes per ha water was supplied. The time of flooding also has a profound effect on yield and structure of swards, the optimum being as soon as possible after green-up of the native vegetation.

Forbs and some toxic plants are considerably restricted by increasing levels of water, thus leaving a larger proportion of acceptable forage in the sward and greatly improving the feeding value of the sward.

Fertilizing

Nitrogen or phosphorus fertilizers are rarely used by herders to improve their grazing pastures due to cost and the difficulty of spreading. Nonetheless, fertilizing can enhance the biomass yield of native pastures, particularly the edible forage. When the sedge-grass meadow referred to above was fertilized once with sulphate of ammonia at the rate of 375 kg per ha (80 kg N per ha) and then flooded with 300 cu m water per ha at the end of June, its edible forage yield reached 5 674 kg DM per ha, an increase of 470 percent compared with the same pasture without any fertilizer. In addition, the green vegetation period of the native sward was extended by an extra two weeks.

Control of toxic plants and rodents

Overgrazing and degradation of alpine rangelands is always associated with an invasion by toxic plants; the greater the overgrazing, the greater is such invasion. The toxic plants commonly found include: Stellera chamaejasme, Achnatherum inebrians, Aconitum szechenyianum, A. rotundifolium and some seasonally toxic herbage from plants such as Ranunculus spp., Pxytropis spp., Gentiana spp., Pediculalis spp., and Senecio spp. The seasonally toxic plants are avoided by animals during the growing season but are grazed in the standing or dry sward. Winter et al. (1992, 1994) reported that species of Senecio are the predominant toxic plants found to be causing large numbers of the deaths among yak on overgrazed pastures in Bhutan. This matter is also referred to in Chapters 8 and 9.

Herders rarely use chemical control of poisonous plants. However, removal of the plants by hand is often carried out. Since most of the toxic plants are broad-leaf, the use of a herbicide, such as 2,4-D, with a dose of 0.454 kg per ha, tends to be used on State farms to remove these plants.

Rodent infestation always follows rangeland degradation and in turn, the rodents accelerate the degradation through consuming both aerial biomass and the roots of plants. The rodents also dig up much soil that then covers the surface of nearby swards. Pika (Ochotona curzoniae) and Chinese zokor (Myospalax fontanierii) are recognized as the most active rodents that invade and destroy degraded meadows, but the alpine steppes and deserts are rarely attacked by these small animals. The pikas move about during the day and Myospalax baileyi at night. The density of the pika distribution tends to increase on the alpine meadow in line with increasing degrees of sward degradation. But the largest number of pikas (148 per ha) is found on medium-degraded meadow. Poison bait casting and setting of rat traps are the most common measures used by herders to remove rodents from their pastures, though sometimes they are not very effective in controlling the periodic infestations. Perhaps an alternative, effective and environmentally friendly means of shrinking the rodent population to within harm-free levels, or eliminating the rodents' habitat, would be to increase the numbers of the rodents' natural enemies, such as the eagle and the fox, or to increase sward height and cover by avoiding overgrazing and through irrigation and fertilizing.

Use of forage crops and sown-grass swards

Given a pattern of native forage production in alpine rangelands as shown in Figure 13.2, an obvious imbalance exists throughout the year between feed supply from pasture provision and the requirements of the animals. The traditional way to solve the issue on the Plateau is to practice an effective seasonal rotation or transhumance system. However, an alternative measure used nowadays by many herders who live at a relatively low elevation in Gansu, Sichuan, Qinghai and southern Tibet, is to sow out a supplementary crop or sward near their permanent houses or near rivers in order to fill some of the forage gap during the cold season. Forage crops are normally the first choice for annual production. For example, oats (Avena sativa) for making into hay and the root crops of sugar beet (Beta vulgaris) and turnip (Brassica rapa) are planted in some relatively low-lying areas or where the temperature is sufficient for their growth.

Alternative supplementary forages are from sown perennial-grass swards that are sometimes established on fenced land. There are several cultivated perennial grass species adapted to the Plateau's harsh climate, such as Clinelumus nutans, Elymus nutans, Bromus inermis, Agropyon cristatum and Poa crymophila. These can be sown in monoculture or in mixture, the latter being the most common. Grass-forage production can be as high as 10 - 14 tonnes DM per ha two years after establishment, i.e. 2- to 5-times higher than the production from enclosed native pasture. In addition, the green-up time of the sown grasses can occur two weeks earlier than that of the native vegetation. However, in the first year of establishment, the sown grasses, because they are insufficiently aggressive, may fail to compete against the native weeds, and so the yield of the sown grass will be lower above ground. However, their root systems can become well established in the year of sowing, and this benefits survival and growth in the second and subsequent years. To achieve both high quantity and quality from the sown sward, an effective control of annual broad-leaf weeds has to be maintained throughout the sward life to ensure persistency.

In terms of haymaking from the cultivated perennial swards, cutting once a year at the early seeding stage and leaving the re-growth for grazing is recommended by Dong (2001). Without a practice of re-seeding, the yield of some monoculture swards begins to decline from the third or fourth year after establishment, while those of mixtures may last for seven to ten years when fertilizer and irrigation are used.

Postscript

The rangelands are not only vast but diverse in climate, topography, soil types and vegetation cover. Sustaining the large populations of yak, sheep, goats and the horses of the herders, as well as wild animals, creates a disequillibrium between the supply of available feed and the requirements of the animals. Typically there is an abundant supply of feed in summer and a significant deficit in winter and spring. Inappropriate but traditional practices have led to substantial degradation of the rangelands, which in turn heightens the difficulties of maintaining an increasing animal population. At the same time, the increasing demands on the rangelands further exacerbate the problems from overgrazing. However, as suggested in this chapter, a study and understanding of the interacting forces and relationships within the ecosystem and the potential for improvements would provide an opportunity for sustainable production from the unique resource represented by the high Plateau and these mountainous regions.

References

Bureau of Animal Husbandry and Veterinary Medicine, Ministry of Agriculture, China (1994). Data on the Grassland Resources of China. Beijing, Agricultural Technological Publishing House, pp. 2-5. (in Chinese)

Chang, D. H. S. (1981). The vegetation zonation of the Tibetan Plateau. Mountain Research and Development, 1 (1) 29-48.

Chang, D. H. S. (1983). The Tibetan Plateau in relation to the vegetation of China. Annals of the Missouri Botanical Garden, 70, 564-570.

Cincotta, R. P. et al. (1991). Forage ecology of livestock on the Tibetan Changtan: a comparison of three adjacent grazing areas. Arctic and Alpine Research, 23 (2), 149-161.

Goldstein, M.C., Beall, C.M. & Cinotta, R. P. (1990). Traditional nomadic pastoralism and ecological conservation on Tibet's northern Plateau. National Geographic Research, 6 (2), 139-156.

Dong, S. K (2001). The stability of mixture grassland of cultivated perennial grass and its regulation in alpine region of Tibet-Qinghai Plateau of China. Ph.D. thesis.

Hu, Z.Z (2000). Prataculture and Environment Development on Qinghai-Tibetan Plateau. Beijing, Tibetanology Publishing House, pp 25-27. (in Chinese)

Hu, Z. Z. et al. (1988a). Studies on primary production and energy efficiency in Tianzhu alpine Kobresia Capillifolia meadow. Acta Ecologica Sinica, 2, 184-192. (in Chinese)

Hu, Z. Z. et al. (1988b). Studies on primary productivity in Tianzhu alpine Polygonum viviparum meadow. Acta Phytoecologica et Geobotanica Sinica, 1, 124-133. (in Chinese)

Li J., Zhu G., Yang T. & Tang S. (1982). Studies of carbon dioxide evolution and cellulose decomposition in soils at the Haibei Research Station of Alpine Meadow Ecosystem. In Alpine Meadow Ecosystem-I, Xia W. (ed). Gansu People Publishing House, pp. 162-172. (in Chinese)

Long, Ruijun et al. (1999a). Feed value of native forages of the Tibetan Plateau of China. Animal Feed Science and Technology, 80, 101-113.

Long, Ruijun et al. (1999b). Effect of strategic feed supplementation on productive and reproductive performance in yak cows. Preventive Veterinary Medicine 38, 195-206.

Long, Ruijun & Ma, Y.S. (1997). Qinghai's yak production systems. In Conservation and Management of Yak Genetic Diversity, Miller, D.J., Craig, S.R. & Rana, G.M. (eds.) Kathmandu, pp.105-114.

Ma Yushou, et al. (1998). Improvement of yak production on deteriorated "black soil" grassland. Grassland of China. (4): 61-63.

Miller, D. J. & Craig, S. R. (1996). Rangelands and pastoral development in the Hindu Kush-Himalayas. Published by International Centre for Integrated Mountain Development, Kathmandu, pp. 75-76.

Ren, J.Z. & Jin, J.H., (1956). Observations on the grazing behaviour yak. Journal of Animal Husbandry and Veterinary Medicine of China, (1) p2. (in Chinese)

Richard C.E. (2002). The potential for rangeland development in yak rearing areas of the Tibetan Plateau. Proceedings of the third international congress on yak, in Lhasa, China, 4-9 September 2000. International Livestock Research Institute (ILRI), Nairobi, pp. 11-18.

Ulyatt, M.J. (1981). The feeding value of herbage: can it be improved? New Zealand Agricultural Science, 15, 200-205.

Winter, H. et al. (1992). Pyrrolizidine alkaloid poisoning of yaks (Bos grunniens) and confirmation by recovery of pyloric metabolites from formalin-fixed liver tissue. Research in Veterinary Science, 52, 187-194.

Winter, H. et al. (1994). Pyrrolizidine alkaloid poisoning of yaks: identification of the plants involved. The Veterinary Record, 134, 135-139.

Wu Ning. (1997). Ecological situation of high-frigid rangeland and its sustainability - a case study on the constraints and approaches in pastoral western Sichuan. Berlin, Dietrich Reimer Verlag. 281 pp.

Xiong, Y. & Li, Q. K. (1987). China soil. (Second Edition), Scientific Publishing House, pp. 284-303.

Zang, J. X., et al.(1991). Contents and distribution of trace elements in alpine meadow soil. In Alpine Meadow Ecosystem-III, Liu J. & Wang Z. (eds.). Scientific Publishing House, pp 257-266. (in Chinese)

Zhang, S. Y. & Ma, Z. Y. (1982). The physiological influence of low temperature at night on some herbage in Tibetan-Qinghai Plateau. In: Alpine Meadow Ecosystem-I, Xia W. (ed.). Gansu People Publishing House, pp 52-57. (in Chinese)

Zhou, S.R, (1984). Study on the forage and feeding habits of yak. A research on the utilization and exploitation of grassland in the northwestern part of Sichuan province. Sichuan National Publishing House, pp.134-137. (in Chinese)

Zhou, S.R & Simon, U. (1995). Evaluation of feeding value on the main rangeland plants on the Tibetan Plateau of China. Proceedings of the fifth International Rangeland Congress, pp: 638-639. Salt Lake City, Utah, July 23-28, 1995.

Zhu Guiru et al. (1982). Seasonal Changes of the number and constitution of the main groups of soil micro-organism. In Alpine Meadow Ecosystem-I, Xia, W. (ed). Gansu People Publishing House, pp 144-161. (in Chinese)