Small Watershed Management and Eco-rehabilitation on the Loess Plateau of China

Transcription

1 Small Watershed Management and Eco-rehabilitation on the Loess Plateau of China Guobin Liu, Junliang Tian, Yumin Chen and Puling Liu Institute of Soil and Water Conservation, Chinese Academy of Sciences and Ministry of Water Resources, NW Sci-Tech University of Agriculture and Forestry, 26 Xinong Road, Yangling, Shaanxi Province , P. R. China, Abstract The Loess Plateau is well known for its deep loess deposits and serious soil erosion. This paper analyses the characteristic of soil erosion on the Plateau and reviews the small watershed management and ecosystem rehabilitation practice and development in the future. In the last 30 years, the government has paid great attention on the integrated small watershed management and restoration of the Loess Plateau. Based on the theory and practice, Chinese scientist presented 28 words strategy and conservational eco-agriculture, developed the integrated health assessment indicators on the Plateau. The further research on small watershed management and ecosystem rehabilitation such as to combine the slope cropland converting with engineering practice, strength on the ecosystem natural rehabilitation and enlarge the management to the medium scale as well as environment effect assessment on conservation practice were suggested. Key words: Loess Plateau, small watershed, integrated management, ecorehabilitation 85 MTT Agrifood Research Finland

2 Soil erosion on the Loess Plateau Soil erosion is a serious worldwide environment problem that threatens the sustainability of agriculture. Loess Plateau with its deep and loose loess, integrity loess-paleosol and serious soil erosion is a special region in the world (Rui Li, 1992; Guobin Liu, 1999). The total loess region has the area of 0.62 million km 2, typical loess area of 0.42 million km 2 and severe erosion area of 0.28 million km 2 which covers 45% of the region with average soil loss of 3720 t/km 2.year, sediment content of 37.6 kg/m 3, which is 14 times in Yangzhi River of China, 38 times in Mississippi River of USA and 49 times of Nile River of Egypt. The maximal soil erosion can be over t/km 2.year (Table 1). Table1. Soil erosion intensity on the Loess Plateau Erosion intensity Erosion modulus (T/km 2.y) Erosion area (10 4 km 2 ) % of total area Very slight Slight Moderate Severe Very severe Extreme > Theory and practice on small watershed management on the Plateau Strategy of soil conservation Professor Zhu Xiamo, a Chinese academician in the Institute of Soil and Water Conservation, CAS & MWR presented a 28 characters strategy of land management on Loess Plateau from his 30-year research and summarization of experience (Zhu, 1993), which is: All rainfall is retained and infiltrated in site; Grain crops are cultivated in plain and table land (terrace, dam land etc.); Wood and fruit trees are located in gullies, and grasses and shrubs are planted on hill sides (all poor eroded land). This strategy has been proved in the practice and plays an important role in watershed management. The Chinese scientist also found an effective way in soil conservation, which is taking small watershed as management unit combining with engineering practice, biological practice and conservation tillage, and improve infrastructure, roads with rational use of land resources in woodland, farmland and grassland. 86

3 Conservation achievements on the Plateau Since 1950s, Chinese government paid a great attention to the soil conservation and agricultural development and invested a lot of money in this region. In 1986, the Ministry of Science and Technology listed the soil conservation and comprehensive reclamation of the Plateau as a State-sponsored key project. The Chinese Academy of Sciences and Ministry of Water Resources in company with the relevant government departments and provinces, set up 11 experimental and demonstrative watersheds as case site for research and demonstration districts in 5 provinces on the Plateau, and established various developmental patterns for top performance of eco-environmental reclamation. The project went on with its implementation till 2000 (Li, 1996). After decade s efforts, a number of significant changes have been seen on the Plateau, including a benign cycle of landscape ecology, big-margin rise in productivity, sound increase in annual grain output and establishment of local fruit industry (Table 2). Table 2. Integrated watershed management on the Loess Plateau Region Watershed Area Controlled area (%) Grain yield (kg/ha) Net income/ Yuan/person/ year Soil erosion (T/km 2.y) Name km 2 a* b* a b a b a b Mizhi Ansai Loess Zhongqi hilly and Guyuan gully Xiji area Dingxi Lishi Xixian Loess Changwu tableland Chonghua area Qianxian a*, average from1985 to 1990, b*, average from 1990 to The implementation of national project of soil conservation promoted the development of science and technology on small watershed conservation and management such as high yield grain crop cultivation, runoff collection and water saving irrigation as well as rational land use planning. Research on soil and water conservation, watershed ecosystem restoration has led to the development of agricultural system that is sustainable. At small watershed scale, comprehensive management schemes and reforestation have conserved water and improved productivity and raised farmer income. 87

4 Stages of watershed restoration and management The implementation of watershed restoration and management is limited by factors like farmer s income, low soil productivity and people s quality in the serious soil erosion region. It takes long time to rebuild the deteriorated ecosystem, and there is a need to proceed step by step. The scientists in Ansai station of Institute of soil and Water Conservation, CAS, presented a principle of conservational eco-agricultural construction, and separated action of restoration for three periods: Initial restoration period, stable improvement period and fine development period (Lu et al., 1997). A. Initial restoration period: The practice in this period is to adjust land use and shift the steep slope cropland to pasture and woodland, to build the levelling terrace and dam land to get high and stable yields. Initial period is very important and hard step by focusing on ecological environment improvement instead of economic benefit. Initial period needs years in the place where investments are made by farmers under the advisory service. Some new techniques are introduced and aid is given in form of plant seeds. B. Stable development period: Once restoration project has started, the main practices in this period are to adjust the inter-relations between partitions of system, increase the input of crop production and improve the benefit of cash crops and pasture gradually, and change the farmer s traditional cultivation methods to customs of conservation tillage on slope land. The characteristic in this period is that ecological benefit somehow equals to economic benefit, and farmers have changed their mono-cultural farming custom, showing more interest in economic benefit to plant more cash crops and realize the importance of soil conservation. This period requires the time of 5-10 years. C. Fine developed period: In this period, the agronomy and agro economy and each partition such as grain yield production, forestry and animal hunsbary in system are well coordinated. Farmers have changed their old custom to pay more attention to growing cash tree and crops. They realize the importance of protection of environment and show great interest in conservation and education. The ecosystem in the watershed has got complicated with multi-farming system and high efficiency and capacity. To reach the fine developed period needs 10 years with 80% area of watershed being controlled. In Ansai small watershed, ecosystem has restored successfully after 20 years practice by the scientist in the Ansai station of the CERN. Farmers improved their income of 8 times and soil erosion reduced over 70% (Table 3). The idea of conservational eco-agriculture and its implementation periodically has been accepted by the local farmers and different decision makers of the government. This case has become a model in loess hilly and gully region. 88

5 Watershed health assessment indicators The ultimate objective of watershed management is watershed health. In Ansai County in northern Shaanxi Province, we restored a small watershed to its original state by mending and rebuilding the depleted ecosystem and ensuring that any further development would be sustainable (Table 3) The watershed was a barren and depopulated gully in Zhifanggou in the hilly heartland of the plateau that had been plagued by serious water loss and soil erosion. Zhifanggou watershed gives a model of how a typical watershed experienced its ecosystem degradation and restoration on Loess Plateau of China. A healthy watershed system will have a relatively stable structure in which ecosystems function well and in which sustainable development can occur. In order to appreciate the benefits of integrated control measures and establish (Liu et al., 1999 and 2002; Walker & Reuter, 1996) corresponding ecosystem rehabilitation processes, it is necessary to assess watershed health. Taking the Zhifanggou watershed as an example, we used HPA to quantitatively assess the health indicators and up scaling to the index of the watershed. Table 3. Zhifanggou small watershed management Year Population Ratio Erosion Yield Cropland (ha/person) I Income c:w:g* t.km 2 Kg/ha total terrace Yuan/person :0.1: :0.5: :0.9: :1.6: :1.6: :2.0: *c: cropland, w: woodland, g: grassland Selection of indicators Health indicators should reflect the factors that influence sustainable development and should reveal the system development tendency (Liu & Fenli, 1998; Liu & Xu, 2002). Identifying and selecting indicators should therefore be objective and quantitative. Diagnosing the health of a watershed is an important aspect of watershed management, which is linked to assessments of environmental quality. In selecting indicators, we considered the hilly and gullied nature of the Loess Plateau; the requirement for environment rehabilitation; and the need for indicators to be objective, scientific, universal, independent and flexible. The indicators for environmental function include vegetation coverage, the realized ratio of primary cropland, soil anti-scour ability and soil organic matter content. The indicators for socioeconomic function 89

6 include the ratio of outputs to inputs in agriculture, the realized ratio of potential food production and the net income per capita. The indicators for comprehensive function were resistible capacity of the system, efficiency of integrated control measures in decreasing soil loss and the total income from industry and off-farm work. The health index was calculated by summing each indicator multiplied by its weight (Table 4). Table 4. Weight of indicators in deferent stage of watershed rehabilitation Initial restoration period: Stable develop period Fine developed period Note: 1-10 is refers as indicators which are: vegetation coverage, the realized ratio of primary cropland, soil anti-scour ability and soil organic matter content, the ratio of outputs to inputs in agriculture, the realized ratio of potential food production, the net income per capita, resistible capacity of the system, decreasing of soil loss and the total income from industry and off-farm work. Assessment of health indicators in Zhifanggou small watershed The time trend of Zhingfanggou watershed health index shown in Fig.1 indicated that the watershed health index was improved from in 1985 to in Our research demonstrated that there have been two periods in rehabilitation: and In calculation of indicators, we gave to the same indicator different weight in those two periods in reflecting the changing of driving force in process of rehabilitation. The indicator of soil quality such as organic matter content and soil anti scour ability were introduced into the index, which showed that the soil improvement delay the economy and productivity changes and that rehabilitation of ecosystem is a long-term process. 90

7 1.0 Health index Time( year) Fig. 1. Health Index in Zhifanggou Watershed on the Loess Plateau The change of health index stages in Zhifanggou watershed reflected the improvement of ecosystem of the watershed since 1985 during initial restoration ( ), stable improvement ( ), and a good development period (1997 on). The results provide scientific support for the theory that restoration of watershed with soil and water conservation measures can be gradually implemented in the region. They also indicated that degraded ecosystems on the Loess Plateau can be restored with 20 years of integrated control measures. Prospective small watershed management and ecosystem rehabilitation Practices have proved that biological, tillage and engineering measures are effective way for small watershed comprehensive control. Since Chairman Jiang Zemin called for rebuilding the north-western China with green mountains and clear river, and former Primer Zhu Rongji put forward 16-words strategy for converting cropland into woodland (or grassland), fencing mountains for re-vegetation, grain food subsidy and family contract, the project of converting cropland to woodland on the large scale was expanded. Taking Shaanxi Province as an example, 104 counties were involved this project including 13 counties of Yan an city. The area of converting cropland was of ha, including ha for converting cropland into woodland, ha for barren mountain reforestation billion kilograms of grain food were provided for farmers who converted cropland into forest land or grassland. Cash subsidy was of billion Yuan (RBM). Implementing the project has enhanced soil conservation and eco-economic development. 91

8 The West China Development Project provides a new opportunity for small watershed control on the Loess Plateau. Soil and water conservation, ecological rehabilitation under the large scale and huge investment and countryside economical development bring forward new requirements for theory and practice on soil and water conservation, and for ecological rehabilitation research. On the basis of the past experiences, the small watershed integrated control should strengthen scientific issue in order to promote ecorehabilitation progress and insure sustainable development ecology, economy and society. Converting Steep Slope cropland into forestland or grassland should follow the regional vegetation distribution, site conditions, biological and ecological characteristics to build mixture vegetation, meanwhile, natural ecosystem restoration capacity should be greatly regarded. Scientific research and ecological rehabilitation practice have shown that vegetation construction on the Loess Plateau should follow the vegetation site condition, characteristics of biological, ecological and community to simulate natural vegetation structure, and choose suitable wood species to plant mixing and multi-layer vegetation. Barren mountains and hills, which occupy 40 to 60% of total area of the Plateau, are restored by taking the advantage of natural restoration ability as a key approach and to put artificial plantation as the second choice. Ecosystem restoration capacity should be greatly regarded and bio-diversity conservation of ecosystem should be protected. Combination of converting steep slope cropland to woodland with gully engineering measures Converting cropland as a core of ecological rehabilitation has strengthened control progress of biological measure. In Loess Plateau, controlling soil erosion should prevent soil loss from hill slopes and gullies and optimize arrangement of biological; conservation tillage and engineering measures in order to effectively reduce soil loss. The model estimated that completely control soil loss from hill slope can only reduce 58% of total soil loss from watershed because gully erosion and gravitational erosion are more developed on the Loess Plateau. Therefore, we should build trap-dam in the gully channels to protect gully slope. On basis of small watershed control, ecological rehabilitation on the Loess Plateau should expand research and experiment to middle and regional scale. Practice has proved that a degraded ecosystem could be primarily restored after years of integrated control. For example, Zifangguo watershed of Ansai, after 20 years of comprehensive control, all slope croplands were converted into forestland or grassland, vegetation cover reached to 48%, 92

9 which could completely prevent soil loss. The health index of watershed ecosystem shifted from in 1985 to in Ecosystem comes into fine development period. As progress of ecological construction, soil and water conservation on large scale should combine regionally economic development and industrial needs. In order to accelerate the construction of converting cropland and to make sustainable development possible, there is a requirement on research and demonstration on middle scale to meet the needs of development at different scale and decision maker. Institute of soil and water conservation has developed experiment and demonstration research area in Yan an city with area of 70.7 km 2. Throuh the project, scientists study the models, arrangements, key techniques and running mechanisms of middle-scale ecological rehabilitation and provide experience and scientific support for local farmers and decision maker. Different scales have different objectives on ecological construction. For the small watershed, ecological construction objective is to protect soil and water resources, and reduce soil loss. The middle scale where taking the county as a unit, ecological construction should combine market requirement and economy development during land use arrangement. The objective of regional ecological construction is ecological security for rivers. Therefore, objective for different scale, and interactions and assessment systems should be researched. Establishing monitoring network of ecological-environment to assess the long term effect on soil conservation practice Effect of soil and water conservation and ecological rehabilitation on regional environmental change should be clearly understood, such as soil water cycle, environmental change, soil erosion intensity, hydrological process, socialeconomic structure, and biodiversity. All impacts are called as regional effects of soil and water conservation and ecological rehabilitation. There were some issues such as artificial vegetation withering caused by soil drought. We have known that conservation practice may reduce the runoff, however, in the long term and large-scale view, we need to know what is its advantage and disadvantage to regional water environment and land productivity. Therefore, we should use current field stations to establish monitoring and research network to find long-term changes of environment during the ecological construction and to assess ecological effects of ecological restoration. Acknowledgments The research was supported by Knowledge Innovation Project of Chinese Academy of Sciences (KZCX1-06), Chinese National Project (2004BA508B14) and China National Key Foundational Development and Planning Project (G ) 93

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