原載《Improving Degraded lands: Promising Experiences From South China》,Bishop museum press, Honolulu, 1993, P139-142

　　Chen Chaohui

　　Guangzhou Institute of Geography

　　Guangzhou, The Peoples Republic of China

　　ABSTRACT

　　Degradation of land productivity caused by soil erosion is a universal problem in tropical and subtropical mountain areas of South China. Managing soil erosion, therefore, is an urgent task.

　　Soil erosion may be divided into three types in accordance with the rockwearhering series. Of these, soil erosion of deeply weathered rock is the most common and most severe type. However, it can be managed using a combination of biological measures and appropriate engineering measures.

　　An ecoeconomic system of multiplelayer agriculture is one available to improve the productivity of eroded land. This has been proved in Wuhua county, Guangdong Province during 19851990 by soil and water conservation experiments and development of agricultural natural resources. This paper intetroductes the experience and its theory.

　　SOIL EROSION MANAGEMENT IN SOUTH CHINAS MOUNTAINOUS AREAS IS AN URGENT TASK

　　Degradation of land productivity by soil erosion is a universal problem in tropical and subtropical mountain areas of South China. In the last 40 years, researchers have undertaken considerable work in soil and water conservation and some beneficial effects have been obtained. However, during this period, because of forest clearing and inappropriate use of hills and mountains, soil erosion has become more serious. Data from nine provinces in South China show the area of soil erosion increased from 60,000 km2 in the 1950s to 170,000 km2 in the 1980s. The soil erosion index in the 1950s was 100300t/km2/y but grew to 300 - 600t/km2/y in the 1980s. The highest erosion rate reached was at least 1,000 - 2,000 t/km2/y resulting in large amounts of soil organic matter being carried away. As a consequence, the land productivity declined or disappeared, agricultural production fell, and the economy declined. Thus, the peoples standards of living were lower in regions of soil erosion than elsewhere.

　　Many regions of significant soil erosion were in poor mountainous areas. Soil erosion in the upper reaches of rivers, however, hindered industrial and agricultural production, whereas the safety of peoples lives and property was more affected in downstream regions. Therefore, wise land management to slow or halt soil erosion, to allow recovery of the lands productivity, to develop production, and improve the economy has become an urgent task in all eroded regions in South China.

　　SOIL EROSION CLASSIFICATION IN ACCORDANCE WITH THE

　　ROCKWEATHERING SERIES

　　Soil erosion may be divided into three types in accordance with the rockweathering series: deeply weathered rocks, lightly weathered rocks, and rock resistant to weathering. The deeply  weathered rocks mainly are composed of granite, Quaternary red clay, and unconsolidated sediments and alluvium. The lightly weathered rocks are mainly rock bind (sandy shale), sandstone and their metamorphic equivalents. Those rocks resistant to weathering mainly are limestone and dolomite and their metamorphic equivalents. The weathered layers of the last two types are thin to very thin and some bedrock is exposed even after slight erosion. Consequently, erosion here can easily and quickly result in the formation of useless land. Related damage from erosion of these two types is less than from the first. Nevertheless, they recover their productivity with difficulty.

　　The depth of weathering coveting fresh granite may be several meters to several hundred meters. Once vegetation is lost and erosion begins, running water will carry a large amount of mud and sand into the rivers. As a consequence, land productivity declines or even disappears, and the eroded and transported sediment produces adverse effects. Furthermore, the distribution of granites rocks is wider in South China and the range of its harm is bigger and more severe. However, because these kinds of hills and mountains have a thick weathered cover, soil erosion can be suppressed using biological measures and related engineering measures that can promote the recovery of the lands productivity and create the necessary conditions for its reuse.

　　The Mechanism Of Managing Soil Erosion With Biological Measures

　　Factors Causing Soil Erosion

　　In hilly and mountainous areas, four main factors affect soil erosion: geomorphy, the makeup of the soilforming rock, climate, and vegetation. Geomorphy, soilforming rock and climate are unchangeable factors but vegetative cover (mainly forests) is a factor that can change. Wherever soil exists with a good vegetative cover, little change in the soils temperature and moisture content will occur. Consequently, the soil materials are not easily washed away.

　　If the forest and other vegetative cover is destroyed, the bare earth will be exposed to a series of physical changes. First, the soil temperature increases and soil moisture evaporation rises. If drought occurs, the soil layers will become dry; when heavy rains fall, erosion will start immediately. In addition, the dry soil layer and the weathered rock layer will absorb water rapidly and transform them into easily erodible mud. In the deeply weathered rock region in the mountains, mud flows or mudrockflows may occur and may even produce big, deep gullies (fall hills). The higher the temperature and the greater the soil moisture reduction, the more the soil absorbs water during rains, and the more the soil erodes. This is why we often see that erosion gullies and gaps of big, deep guillies mostly exist on southwest and western slopes of hills and mountains and less so on north slopes. Because the temperature is higher here and the moisture of the sunfacing slopes are much less than on other slopes, the soil layer and the weathered layer are more easily dispersed and washed away. Certainly, the steepness of the hills and mountains plus the more southerly rains in these regions also promote soil erosion

　　To Restore Forest Vegetation Is The Most

　　Important Measure For Promoting

　　Improved Land Productivity

　　 Forest vegetation can be restored by human actions or by natural regrowth. Forests not only protect the earths surface from erosion and anchor the soil layer, but they also decrease the change of temperature and moisture of the soil, reduce evaporation of soil water, increase and hold soil moisture and strengthen the soil.  Thus, forests enhance the antierosion capacity of the soil and enhance development. Biological measures, therefore, are the fundamental measures for managing soil erosion. However, sometimes it is also necessary to use some engineering measures in areas where big, deep gullies or erosion gullies exist. Engineering measures can only trap sand and soil.If not combined with biological measures, engineering efforts alone will fail under natural forces. Biological measures also are unique ways to develop economic benefits.

　　Building A Multiplelayer Agricultural

　　Ecoeconomy System To Promote Recovery

　　Of Land Productivity

　　The HezikouXinyi District was selected as the Synthetic experiment region to launch a pilot research effort for management of soil erosion and the development of agricultural natural resources. This effort was supported by Domain Department of the State Planning Commission, China Academy of Sciences, Domain General Office of Guangdong Province and other concerned departments, the Synthetic Science Investigating Team of the Hill and Mountain District, and organized by the Guangdong Academy of Sciences and The peoples government of Wuhua County. In the last five years, the work has produced some successful results. My main duty in the experiment was to design and conduct research on agriculture production allocation. The main function was to arrange the order of a multiplelayer agricultural production system.

　　The Experimental Region

　　HezikouXinyi Synthetic Test Region, covering about 235 km2, is situated in north Wuhua County of eastern Guangdong Province (Figure 1). Twothirds of the area is a hilly and mountainous region of the Wuhua River basin. Granite is the main type of bedrock making up the hills and mountains, yet part of the mountains are composed of sandy shale (rock bind) and metamorphic rocks.

　　The climate here is subtropical monsoon. The mean annual temperature is 212℃ and the mean annual precipitation is 1,418 mm most of which falls from April to September. Heavy rains during this period lead to flash floods and soil erosion. The eroded area covers 66 percent of the total land area.

　　In 1985, population of the 276 ha of cultivated land was 5,580. The per capita income in 1985 was only RMB 333 yuan. It is a highly populated, poor, mountainous area having more mountains than cultivated land, low income, and severe soil erosion.

　　For a long time, the regions forests and vegetation have been used heavily for rural energy needs and for economic products. Such use led to soil erosion, caused degradation of the ecosystem and damaged agriculture, and hindered economic development. Therefore, the people in this region are eager to solve the soil erosion problem.

　　The Target And Main Measures Of Managing Soil Erosion

　　Through investigation and gained experience, the targets of managing soil erosion are as follows:

　　Low capital investment, rapid effect; improved rural income, and getting tangible results. To achieve these targets it is necessary to take certain measures and follow certain principles:

　　a. Biological measures should be combined with engineering measures, with biological measures taking the lead role.

　　b. It is necessary to avoid opening the earths surface as much as possible. When undertaking engineering measures, the "earthskin vegetation" (lichens, bryophytes, etc.) should be protected. 

　　c. When combining trees, shrubs and grass during biological reclamation measures, plant grass before planting trees to minimize erosion, improve the soil, and improve tree growth.

　　d. Management must be combined with development.

　　e. Use a small river basin as a geographical unit in which to build an ecoeconomy system of multiplelayer agriculture. A basin is a good unit to use with synthetic management of soil erosion and for synthetic development of agricultural natural resources.

　　The Procedure And Results Of Management

　　The investigating team drew up a fiveyear experimental research plan. The plan included: (a) vegetation recovery, (b) engineeringmanagement works, and (c) adjustment of the landuse structure.

　　a. Vegetation recovery-Vegetation recovery is the key element in managing soil erosion. It includes planting fruit trees and other trees, and pasture grasses. The hills and mountains in the experimental site were used as follows: hilltops were planted with a mixture of coniferous and broadleaf trees; hillsides were planted with a dual purpose forest-a forest for water and soil conservation and a forest for timber, fuelwood, and other economic uses; the foothills were planted with fruit trees and pasture grasses.

　　From 1985 to 1990, 9062 ha of forest were planted for all of the various uses. Treeplanting densities were 2,250 - 2,270 trees/ha. In addition, forage species were planted under the forest or fruit trees leaving no barren hills and mountains in the experimental region.

　　soil and water conservation forest 　　　　4407 ha

　　fruit forest                        　1811 ha

　　economic forest                     　533 ha

　　firewood forest                     　235 ha

　　pasture                            　750 ha

　　other                             　1326 ha

　　b. Engineering measures-Keyengineering constructions mainly included sand dams downstream of the gaps of collapsed hills. Nineteen such dams have been built since 1986. Other engineering construction included some ditches in the gully erosion area.

　　c. Comprehensive management in valley flats-Road and ditch repairs were undertaken to transform fields and lowlands for development of multiplelayer agriculture. These activities were part of comprehensive management for increasing landuse capabilities.

　　During five years, the peasants repaired 11 km of roadway and 2,066 m of irrigation and drainage ditches, transformed 933 ha of midoutput or lowoutput fields into fertile fields, and constructed 9 ha of fish ponds and dikes. The dikes were used as sites to plant fruit trees, such as litchi and orange, and were used for pasture as well; ponds were used to raise fish. The peasants worked hard to develop livestock, raising mainly pigs and chickens.

　　After taking the above measures, a multiplelayer agricultural ecoeconomy system existed here. Vegetation in the experiment region has recovered and soil erosion basically has been controlled. By 1990, the river bed had cut downward at least 60 cm, necessitating dam construction to prevent further riverbed erosion. The combination of biological and engineering actions restored vegetation which enhanced the selfrestoration of the lands productivity. Much of the wasteland has become usable once again, and many fields once covered by sand now have been planted with fruit trees.

　　The landuse capacity in the experimental region reached 92% in 1990, 635 times higher than in 1985.Total crop output per unit area has increased. For example, the total yield volume of provisions in 1990 was 2,394t, an increase of 203% over 1985. The per unit area yield of rice increased 136%.  The oil crop output increased 395%, reaching 266 t. Fruit production, livestock raising, and fisheries developed rapidly. Fruit gardens reached 240 ha, 516 times as great as in 1985. Fruit output was 88 times larger than in 1985. The output of pigs increased 27 times. The fishpond area was enlarged to nine ha and the output of fresh fish reached 518t, an increase of 36 times over 1985 and its per unit area yield increased 24 times. Consequently, the per capita income of the peasants increased 21 times over that of 1985.  Hezikou has become the richest village in Wuhua County.

　　Meanwhile, many measures were taken to solve the rural energy problem. These included: importing coal from other regions, constructing biogas generators, and disseminating fuelsaving stoves. Consequently, the forest resources were relieved from local pressures and good management of soil erosion has been achieved.

　　The experiment proved that to build a multiplelayer agricultural ecoeconomy system, taking biological measures as the main activity and combining them with necessary engineering measures, is a successful method to manage soil erosion and to improve productivity of degraded lands. This approach may be extended for usein other places.