Published in J. Environ. Qual. 33:1675-1681 (2004).
© ASA, CSSA, SSSA
677 S. Segoe Rd., Madison, WI 53711 USA
TECHNICAL REPORTS
Ecosystem Restoration
Regional Analysis of Climate, Primary Production, and Livestock Density in Inner Mongolia
Mei Yua,*,
James E. Ellisb and
Howard E. Epsteinc
a Laboratory of Quantitative Vegetation Ecology, Institute of Botany, The Chinese Academy of Sciences, Beijing 100093, P.R. China
b Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO 80523
c Department of Environmental Sciences, University of Virginia, Charlottesville, VA 22904
* Corresponding author (meiyu{at}ibcas.ac.cn).
Received for publication June 17, 2003.
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ABSTRACT
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Overstocking is believed to be one of the principal causes for grassland degradation in northern China. For this reason, quantification of overstocking and spatiotemporal analysis are needed for this area. In this study, the relationship between annual rainfall and grassland aboveground net primary production (ANPP) was analyzed using data from 1982 to 1991 in the Inner Mongolia Autonomous Region (IMAR), China. Subsequently, rainfall-based livestock carrying capacity was estimated and combined with livestock density calculated from county-level livestock data from 1982 to 1991 to determine spatial and temporal patterns of a stocking rate index and its relationship with climatic factors. The results indicate the following. First, there was a significant linear relationship between annual rainfall and ANPP in IMAR and the slope of ANPP versus rainfall was greater than those found in South America and Africa, indicating higher rain-use efficiency. Second, temporally averaged livestock density showed overstocking in most of the rural counties except for those in the cold north, where human populations are low and transportation systems are poor. Third, the stocking rate index increased with temperature, from less than 1.0 in the north, to greater than 2.0 in most of the southern IMAR. Within the central IMAR, the index increased from west to east, along the gradient of increasing rainfall. Fourth, long-term dynamics of livestock density depicted continuous overstocking, more than 20%, from 1982 to 1991 along the western part of the NorthEast China Transect (NECT) within IMAR. Spatial planning of livestock densities according to carrying capacities and improved pastoral management are needed in this area.
Abbreviations: ANPP, aboveground net primary production • IMAR, Inner Mongolia Autonomous Region • NECT, NorthEast China Transect
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INTRODUCTION
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AS ONE OF the largest grassland regions in the world, the rangeland ecosystem of northern China has experienced severe degradation during the last century, with more than 20% described as unusable and about one-third as degraded (Committee on Scholarly Communication with the People's Republic of China, National Research Council, 1992; Sneath, 1998). Overstocking is believed to be one of the principal reasons for degradation in this area (Committee on Scholarly Communication with the People's Republic of China, National Research Council, 1992; Sneath, 1998; Verburg and van Keulen, 1999). On the other hand, climate variables, especially rainfall in semiarid and arid areas, have overriding effects on grassland production, and thus affect livestock carrying capacity.
The relationships among rainfall, grassland production, and herbivore biomass have been analyzed for both natural and agricultural ecosystems (Coe et al., 1976; Lauenroth, 1979; Kalff et al., 1985; Oesterheld et al., 1992, 1998; Paruelo et al., 1999; Jobbagy et al., 2002). Modeling efforts have been made to address these relationships in a series of studies by Gao and Yang (1995) and Gao et al. (1996a)(1996b, 1998). A predictive model for carrying capacity, determined directly from rainfall, was established by Coe et al. (1976) based on data mainly from natural ecosystems in Africa. Oesterheld et al. (1992) developed separate regression models between aboveground net primary production and herbivore biomass for wildlife and livestock based on data from South America. They reported that the herbivore biomass supported per unit of primary productivity was about an order of magnitude greater in agricultural than in natural ecosystems.
The Inner Mongolia Autonomous Region (IMAR), with a total area of nearly 1.2 million km2, 73% of which is grassland, is a transition zone between arable farming and pastoralism. The area has been called agricultural–pastoral mixed belt, characterized by a combination of rangeland-based livestock systems and mixed farming systems. The "pastoral" region of China is in the northwestern IMAR, where livestock was mainly kept under grazing, while the "agricultural" area, characterized by intensive arable farming, is in the eastern region, where livestock was kept in either mixed farming systems or in zero-grazing production systems fed by products from elsewhere (Verburg and van Keulen, 1999). The IMAR has a sharp annual rainfall gradient, from 600 mm in the east to less than 100 mm in the west. Most of the rainfall occurs from May to September, coinciding with high temperatures. The coincidence of high moisture and high temperature contributes to higher rain use efficiency than in most other rangeland areas in the semiarid and arid regions (Lauenroth, 1979; Le Houerou et al., 1988; Austin and Sala, 2002). Annual grassland net primary production, a widely used index to estimate annual fodder available in this area (Zhao et al., 1988; Wang et al., 2003), is highly variable and strongly related to rainfall.
From east to west, the vegetation in IMAR can be classified as mountain forest, meadow steppe, typical steppe, desert steppe, steppe desert and desert, with meadows in the lowlands and croplands in the river valleys in the east and central south (Fig. 1). Remote-sensing surveys indicated that, on average, 4.7 Mha of grasslands in the northern steppe region of China were added to the degraded area each year (Li, 1990). At the same time the numbers of livestock have exceeded carrying capacity in many areas (Li, 1990).
Quantification of grazing pressure and its spatial and temporal patterns are needed for IMAR. Our objectives in this paper are to (i) investigate the relationship between rainfall and aboveground net primary production (ANPP) of the grasslands in IMAR, and use rainfall to estimate livestock carrying capacity; and (ii) compare long-term county-level livestock density data and the estimated rainfall-based carrying capacity to identify spatial and temporal patterns of grazing pressure within the region.
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MATERIALS AND METHODS
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Data Collection and Organization
The data sets we used included rainfall, vegetation type, ANPP, county-level livestock numbers, and county boundaries. Cities with large urban areas were treated as special counties. This classification is different from the general system in western countries where cities are always within counties. Annual rainfall data from 1982 to 1991 were collected from 98 weather stations in IMAR from the China Meteorological Administration. The 1:4000000 vegetation map (electronic copy from the Institute of Geographical Sciences and Natural Resources Research, The Chinese Academy of Sciences) was used in this study. Aboveground net primary production data were collected from 18 sites during the period 1984–1990, covering meadow steppe, typical steppe, desert steppe, steppe desert, and desert (Li, 1993). Annual county-level livestock data included numbers for total large livestock (cattle, horses, camels, donkeys, and mules), and for total small livestock (sheep and goats) from 1982 to 1991 (Inner Mongolia Autonomous Region, 1983–1992). We also collected the annual numbers for each population of cattle, horse, camel, donkey, mule, sheep, and goat at the county level for both 1982 and 1983 (Inner Mongolia Autonomous Region, 1983 and 1984).
Relationship between Rainfall and Aboveground Net Primary Production and Estimation of Livestock Carrying Capacity
Although the regression model developed by Coe et al. (1976) is a simple way to predict rainfall-based carrying capacity, a disadvantage is that it was generated mostly from wildlife data, not livestock. According to Oesterheld et al. (1992), using this model may underestimate the carrying capacity for livestock. In addition, since the regression was based on data from Africa, a further underestimation may result from a different rainfall pattern and rainfall use efficiency in IMAR. Therefore, the relationship between annual rainfall and ANPP for IMAR was quantified based on the available data. Aboveground net primary production (g DM m–2) was correlated to annual rainfall for the 18 sites using the following model:
 | [1] |
where R is annual rainfall (mm) and a0 (g m–2) and a1 (g m–2 mm–1) are intercept and slope of the linear model, respectively. Equation [1] was substituted into the relationship between net primary production and livestock carrying capacity (Oesterheld et al., 1992) to obtain a composite model for the relationship between livestock carrying capacity and annual rainfall for IMAR:
 | [2] |
where B is livestock carrying capacity expressed as livestock biomass (kg km–2).
Mean annual rainfall data from 98 weather stations were spatially interpolated for the whole of IMAR with the inverse-distance-weight (IDW) method embedded in ARC/INFO (Environmental Systems Research Institute, 2002) (Fig. 2). A rainfall-based carrying capacity map for IMAR was created using the composite model (Eq. [2]). Finally, the carrying capacity map was integrated spatially to derive the average carrying capacities for the counties.
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Fig. 2. Spatially interpolated map of average annual rainfall (mm) in the Inner Mongolia Autonomous Region, 1982–1991.
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County Livestock Density
We divided the livestock in IMAR into two categories, large and small in body weight. The proportions of numbers of the animal types within the large category and those within the small category vary among counties. For instance, the proportions of numbers on cattle are high in the east, while those on camel are high in the desert in the west. We used the data on numbers of each animal type at county level for 1982 and 1983 to calculate the proportions of numbers on different types within the large category and those within the small livestock category. These ratios were used to calculate county-level livestock biomass in standard stock units from the numbers of large and small livestock, respectively, from 1982 to 1991. The body weights for each livestock type used in this calculation are 388 kg for cattle, 573 for camels, 325 for horses, 325 for mules, 318 for donkeys, 64 for sheep, and 44 for goats (Humphrey and Sneath, 1996; Holechek et al., 1998). The livestock biomass in standard stock unit was calculated as:
 | [3] |
where SSU is the livestock biomass in standard stock unit (kg); wil and wjs are the body weights for each livestock type within large and small livestock categories, respectively; pil and pjs are the proportions of numbers of different livestock types within large and small livestock categories, respectively; indices i vary from 1 to 5 and j vary from 1 to 2; and 
pil = 1, 
pjs = 1, and nl and ns are the numbers of large and small livestock, respectively.
County-level livestock density was expressed both with respect to total area and grazed area, assuming that meadow, meadow steppe, typical steppe, desert steppe, steppe desert, desert, and sandy shrubland are the vegetation types suitable for grazing.
Spatial and Temporal Grazing Pressure Patterns
We defined a stocking rate index as the ratio of livestock density to rainfall-based carrying capacity to express grazing pressure, based on both total area and grazed area. A map of county-level stocking rate indices was generated with ARC/INFO (Environmental Systems Research Institute, 2002) to visualize the spatial patterns of grazing pressure. Then, the relationships between spatial grazing pressure distribution and climatic factors were investigated by comparing the spatial patterns of stocking rate indices with those of rainfall and temperature.
To analyze the effect of rainfall specifically, and to investigate the temporal pattern of grazing pressure, we selected the western part of the NorthEast China Transect (NECT) (International Geosphere and Biosphere Program, 1995) within IMAR as a study region. The NECT, an International Geosphere Biosphere Program (IGBP) transect, is centered at 43.5°N and extends 1400 km from east to west (Gao and Zhang, 1997; Gao and Yu, 1998) following a sharply declining rainfall gradient. The western part of NECT within IMAR (NECT_IMAR) is about 900 km in length, and annual rainfall decreases from more than 400 mm in the east to less than 200 mm in the west, supporting the grassland types of meadow steppe, typical steppe, and desert steppe from east to west. Annual stocking rate indices were calculated for the counties along NECT_IMAR from 1982 to 1991.
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RESULTS AND DISCUSSION
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Relationship between Rainfall and Aboveground Net Primary Production
Peak aboveground biomass increased with precipitation (r2 = 0.68, p < 0.05; Fig. 3). The slope of the regression line, 0.55 g m–2 mm–1, exceeds those found from similar studies in South America and Africa (Coe et al., 1976; Lauenroth, 1979; Le Houerou et al., 1988; Sala et al., 1988; Epstein et al., 1997; Austin and Sala, 2002), implying a higher rain-use efficiency in IMAR, while the slope is within the range 0.5 to 2 g m–2 mm–1 proposed by Noy-Meir (1973). The "ineffective precipitation" or "zero-yield intercept" was 46.5 mm yr–1, that is, higher than the 29 mm yr–1 reported by Lauenroth (1979) and lower than the 56 mm yr–1 by Sala et al. (1988), but within the range 25 to 75 mm yr–1 proposed by Noy-Meir (1973). We excluded the data for the sandy area of Ordos Plateau from the regression because the peak aboveground biomass in this area was much lower than that in other areas with similar annual rainfall. One possible reason might be the poor nutrient conditions in these sandy soils. When trying to develop a regression specifically for the Ordos Plateau, the data points were widely scattered due to its spatial heterogeneity (Li, 1990; Gao, 1997; Gao et al., 1997). Exclusion of Ordos Plateau may have resulted in overestimation of ANPP and corresponding livestock carrying capacity for most counties in the Ordos Plateau.
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Fig. 3. Relationship between annual rainfall (mm) and peak aboveground biomass (PAB, g m–2) in the Inner Mongolia Autonomous Region (solid line = regression line, broken line = 95% confidence limits).
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County Livestock Carrying Capacity and Density
Spatial patterns of average livestock density per county from 1982 to 1991 are shown in Fig. 4. Livestock densities based on total area (DEN_t) and grazed area (DEN_g) indicate that DEN_t for most of the cities and DEN_g for the counties within the cropland zone were very high in comparison with the calculated carrying capacities. This may be partly due to the fact that livestock at these sites were mostly stall-fed. The same can be seen from the maps of livestock densities in Inner Asia for 1992 (Color Plates 2–4 in Humphrey and Sneath, 1996). In subsequent analyses, we concentrated on rural counties and excluded those within cultivated areas. In general, livestock carrying capacity increased with rainfall, and average livestock densities exceeded carrying capacities for most of the counties (Fig. 5). However, in several counties in high-rainfall areas, livestock densities are relatively low in comparison with the corresponding carrying capacities. These counties are either located to the north, in a cold region with relatively low human populations, or in the Daxinganling mountain area, with poor infrastructure. These results are compatible with one economic conclusion from the work of Verburg and van Keulen (1999).
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Fig. 4. County average livestock density (kg km–2, based on total area) in the Inner Mongolia Autonomous Region, 1982–1991.
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Fig. 5. Average rainfall-based carrying capacity (RBK, kg km–2) and actual livestock density (kg km–2, DEN_t denotes the density based on total area, while DEN_g indicates that for grazing areas only) for the rural counties in the Inner Mongolia Autonomous Region, 1982–1991.
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Spatial Patterns of Stocking Rate Index and Their Relation with Rainfall and Temperature
Stocking rate indices (SRI) exceeded 1.0 for most areas, which indicates possible overstocking (Fig. 6). In addition, the livestock densities were more than twice the carrying capacities (SRI > 2) for all counties with annual rainfall below 200 mm and for some counties with annual rainfall between 300 and 450 mm. Generally, stocking rate index increased from below 1.0 for most of the sites in the northern part of IMAR, to 1.0 to 2.0 for most counties in the central part, to 2.0 to 4.0 for most of the counties in the south with increasing temperatures (Fig. 7). Stocking rate indices of >4.0 were found around cities or in counties within the cropland area. In the central part of IMAR, stocking rate index increased from west to east, with increasing rainfall. The exceptions in the southern part of IMAR were the counties in the Ordos Plateau, with relatively lower stocking rate indices. As indicated, this is the result of the overestimates of ANPP and carrying capacity for these sandy soils with low fertility.
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Fig. 6. Average stocking rate indices (SRI_t and SRI_g represent the stocking rate indices based on total and grazing areas, respectively) for the rural counties in Inner Mongolia, 1982–1991.
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Fig. 7. Spatial patterns of average stocking rate indices based (a) on total area and (b) grazing area from 1982–1991 in the Inner Mongolia Autonomous Region (IMAR) (stars represent cities).
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Long-Term Livestock Density and Stocking Rate Index along the West Part of the NorthEast China Transect and Their Relations with Rainfall
Annual livestock densities for all years consistently exceeded carrying capacities (stocking rate indices greater than 1.2) for every county within the western NECT (Fig. 8). However, there was no significant systematic temporal trend for annual livestock densities during the period from 1982 to 1991.
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Fig. 8. Livestock carrying capacity, annual density [kg km–2, based on total area (a) and grazing area (b)], and stocking rate indices [based on total area (c) and grazing area (d)] for the rural counties along the NorthEast China Transect (NECT) of the Inner Mongolia Autonomous Region (IMAR), 1982–1991. Values in parentheses in the legend denote average annual rainfall.
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All counties with average annual rainfall below 300 mm had annual stocking rate indices below 2.0; while the counties with average annual rainfall greater than 300 mm mostly exhibited annual stocking rate indices greater than 2.0, with the exception of Keshiketeng County.
Implications for Future Agro-Pastoral Management
Our analysis shows that most areas in IMAR have been overstocked for the 10 years of the analysis. Analysis from long-term remote sensing data at Xilingol River basin, located in southeastern part of the IMAR, indicated that degraded and sandy areas increased during this period (Xiao et al., 1997; Wang et al., 2003). Meanwhile, continuously heavy sandstorms starting from 1993 indicated that close attention must be given to grassland management in IMAR.
The simplest solution to the overgrazing problem is to reduce the number of livestock in the overgrazed area. However, with the high economic and population pressures in IMAR, this solution is impractical. Our analysis suggests the following alternatives. First, spatial planning of domestic livestock numbers and densities according to the calculated carrying capacity is needed. Our analysis revealed that some areas still have stocking rate indices below one, indicating potential for livestock expansion. Second, increasing the carrying capacity by improved pastoral management is needed. Livestock carrying capacity might be increased by increasing livestock mobility (Sneath, 1998) and by improving grass quality, such as introducing improved breeds of forage species (Wang, 1992; Chen and Wang, 2000). These practices can improve ANPP, so that livestock carrying capacity is increased.
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CONCLUSIONS
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We analyzed the relation between annual rainfall and aboveground net primary production for the grasslands and deserts in IMAR, and estimated rainfall-based livestock carrying capacities at the county level. In comparison with livestock density, the spatial and temporal patterns of stocking rate indices were analyzed in relation to climate. The following conclusions were drawn from the analysis. First, average livestock densities from 1982 to 1991 exceeded carrying capacities for most rural counties with the exceptions of those located in the cold north with low human density and those in mountainous regions with poor infrastructure. Second, with increasing temperatures, stocking rate index increased from below 1.0 in northern part of IMAR, to 1.0 to 2.0 for most of the counties in the central part, to greater than 2.0 in most southern counties. Within central IMAR, the stocking rate index increased from 1.0 to 2.0 in the west to more than 2.0 in the east, along increasing rainfall. Third, continuous overstocking was revealed for counties along NECT_IMAR from 1982 to 1991. The annual stocking rate indices were above 2.0 for most rural counties in high-rainfall areas (annual rainfall > 300 mm), while below 2.0 for others. Fourth, spatial planning of livestock densities according to carrying capacity, as well as improved pastoral management to increase carrying capacity, are needed in this area.
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ACKNOWLEDGMENTS
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This research was jointly supported by The Ministry of Science and Technology of China under Grant G2000018605, The National Science Foundation of China under Grants 90202008 and 90211002, and The National Science Foundation Grant of the United States "Integrated Assessment of the Effects of Climate and Land Use Change on Ecosystem Dynamics, Stability and Resilience on the Mongolian Steppe."
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TOP
ABSTRACT
INTRODUCTION
