Techniques for Establishing Shelterbelt System around Oasis and Its Benefit in Xinjiang

 

Liu Yuhua   Liu Kang

(Xinjiang Academy of Forestry Sciences, Urumqi 810000)

 

Abstract:  Xinjiang Uygur Autonomous Region is the largest arid desert province in China, the eco-environment is fragile. It makes the oases that take 4.2% of the total area of the whole Xinjiang face up with a series of environmental problems. This paper discusses the structure, function and benefit of the shelterbelt system around the aoses in general.

Key words:  oasis; shelterbelt system; ecological benefit; economic benefit

 

            Located in the inner land of Eurasia, the Xinjiang Uygur Autonomous Region is situated in the west-northern part of the Peoples Republic of China, is far away from seas and oceans, is surrounded by mountains, also is the largest arid desert province in China. In Tarim basin of the southern part of Xinjiang with the temperate zone desert, the annual temperature is 9-12℃, the accumulated temperature of ≥10℃ is 3,700-4,300℃, the precipitation is 10-50 mm, the evaporation is 2,300-2,900 mm; In Junggur Basin of the northern part of Xinjiang with the frigid temperate zone desert, the annual temperature is 3.6-5.7℃, the accumulated temperature of ≥10℃ is 2,395-3,140℃, the mean precipitation is approximately 100-200 mm, and the mean evaporation is 1,000-2,000 mm.

            Xinjiang is vast in territory, the total land territory is 165×104km2, among which the mountain area takes 49.5%, the desert area covers 22.5%. The oases in Xinjiang are distributed around the basins in accordance with the water systems with narrow shape or strip shaped, all of which are close to desert or surrounded by deserts and Gobi, and occupy 4.2% of the total land area of Xinjiang.

1 Eco-environmental Problems in Oases

 

            In Xinjiang, the desert area is large, the quantity of heat is surplus, the water resources is insufficient, the vegetation is rare, the ecological system is fragile, as well as the pressure of the population growth is serious. As a result of the reasons as mentioned above, there have been a series of eco-environmental problems in the oases. (Zhu Xunyu, 1986) The serious wind-sand disaster: under the resultant impacts of general circulation and local circulation, the weather is with more gales and dry-heat winds. The annual gales (≥8 scale) is 10-30 days in most part of the region, in the areas of wind gap and river valley regions, it is more than 100 days, in every 5-10 years there is one invasion of strong and cold wind, with the maximum wind velocity of 40m/s, which makes hundred thousands ha Of crops and more than one million domestic animals sustain a crushing losses. There are 8-15 days of dry-heat winds in a year, in the seriously impacted area, it can be more than 20 days, the reduction rate of wheat output is 10-20%; (Xinjiang forest association, 1986) The extension of desert area: the arid and more winds are the natural factors of desertification, while plunder-like cut of forest, and over-grazing are the main reasons which lead to the activation of fixed sand dunes. In recent 40 years, the reduction rate of plant community distribution of Holoxylon ammodendron in the northern part of Xinjiang is 68.4%; in the southern part of Xinjiang, the reduction rate of the plant community distribution of Populus euphratica is 46.9%, the reduction rate Tamarix spp. is 40.5%. The desert area within the whole Xinjiang has increased from 37×104km2 in 1950s to 42.1×104km2 in 1990’s; (Liu Minting, 1986) The strong development of secondary soil salinization: because of the dry climate, the precipitation is rare, adding the canal system seepage, and over-irrigation and mis-management of water resources, the salinized farming land has been enlarged to 1 million ha in 1980’s from 66.7×104km2 in 1960s, which takes about 1/3 of the total areas of the cultivated land in Xinjiang; (Xu Jinfeng, 1986) The agricultural production in some districts is in the state of vicious circle: the four materials in vast farming region are deficient, which leads to the undue collection of forest and high carrying capacity. In whole Xinjiang, there is 24.5%×104t of straw being burned as cooking and heating materials every year, the content of N,P,K containing in which is equal to 6.7-8.9×104t standard chemical fertilizer, making the wind-sand disaster spreading, the soil fertility was decreased, the agricultural production in some districts is in the state of vicious circle.

 

2 Model of Oasis Shelterbelt System and Its General Construction Situation

 

            According to the characters of Xinjiang oases, a set of suitable construction models of shelterbelt system has been worked out, which is that in the periphery of the oasis to build shrub-grass belts or to construct windbreak and sandbreaks; in the border district of the oasis to build stem forest belts: in the interior of the oasis to build forest networks protecting farmlands with features of narrow forest belt and small networks; in the region establishing shelterbelts system and tree network to carry out the advanced cultivation between agriculture and forestry, in the interior and periphery of aoses to build small-scale cash trees, community forests and large-scale fuelwood and grazing land protective shelterbelts. Thus, from the periphery to the interior of the oasis, based on the different demands, the establishment of different kinds of shelterbelt system and tree network that consists of tree plantation in the oases have to be evenly distributed, and be rationally arranged in consideration of the construction of complex ecosystem which is composed of tree, shrub and grass.

            In arid desert area, how to utilize rationally the limited water resources is the key solution to construct successfully shelterbelt system. To the farmland protective forest, besides persisting in arranging water according to the proportion of agriculture area to the forest area, adjusting crop structure, arranging a part of spring water to replant, mainly adopts the model of narrow forest belt and small network in combination with canal, road, shelterbelts and farmland on the basis of the master plan. As a result, less crop-farming land can be occupied, less water resources is wasted, less investment for reaforesting can be input, the functions of both farmland protection and timber harvest can be obtained, the ecological and economic benefits are obvious, and villagers would accept this techniques for implementing the local area integrated development programme with great interests.

            As for the large-scale fuelwood and fodder plantations, windbreak and sandbreaks, and the complex biological system of shrub-grass, it is designed that they should be developed according to the characters of water resources in different regions. In the northern part of Xinjiang, there is plenty of snow in winter, and some precipitation in growth season, it is stressed that the shrub-grass belts should be recovered and revegetated through hard efforts for fixing sands and breeding grass, for instance, taking Holoxylon ammodendron as the pioneer native species; in the southern part of Xinjiang, summer floods are wisely used to restore and rehabilitate shrub such as Tamarix spp. and Elaeagnus oxycarpa, and to construct fuel energy and fodder plantations.

            The construction of oasis shelterbelt system in Xinjiang, because of the acceptable measures, rational arrangement, the developments of agriculture and animal husbandry is effectively promoted, especially since the development of Three North Project of Shelterbelt, both the development speed and the afforestation quality reach the progressive level, by 1995, the conserved area of afforestation in Xinjiang is 51×104km2, among which the area of various kinds of shelterbelt is 21.3×104km2 (The 65% of farmland in Xinjiang is well protected by the shelterbelts), of energy and fodder plantation is 8.5×104km2, of cash tree is 13.6×104km2, and of community forest is 6.8×104km2.

 

3 Economic and Ecological Benefits of Oasis Shelterbelt System

 

            The oasis shelterbelt system comprising many kinds of forests, because of the different functions of various kinds of forest, the ecological and economic benefits are remarkable.

 

3.1 The shrub-grass belt in the periphery of oases

            The shrub-grass belt is designed to control the sand sources, to prevent the fringe area from wind erosion, and to limit sand accumulation around the oases. The result of the detail studies show that, in the interior of shrub-grass belt with the height of 50-60 cm, the roughness is increased 8×104-3×105 times than that in the eroded bare land and silt flatland. The friction velocity is increased 4-5 times, and consequently, the wind velocity in the layer near the ground has been reduced; the more it is near the ground, the more wind velocity reduced; when the reduction rate of wind is 40% at the height of 50 cm, the wind velocity will be declined about 90% at the height of 10 cm above the ground. The functions of shrub-grass belts for controlling erosion and stablizing mobile dunes are closely related to some factors such as plant component, coverage, width and so on. In the eroded area, when the plant coverage reaches above 65%, the surface soil is stable and erosion is impossible; while in the sand accumulated area, when the plant coverage reaches above 40%, the vegetated dunes could avoid the activation of sand dunes. Based on the observation to the total sand movement under the wind and sand flow impacts, the shrub-grass belt with the width of 100 m could control 90% of the total sand movement; when the width is 244 m, about 97% of moving sands could be fixed. The arrangement width still considers the sand sources, the seasons with frequent strong winds. In general, the width of shrub-grass belt should not be less than 200 m, under the circumstance of having capabilities, the more wide the belt is, the better result it produces. Simultaneously, it is emphatically stressed that the nutritive value of some kinds of xerophyte of shrub and grass with very strong resistance that are adopted on a large scale in Xinjiang is equal to the 42-63% of that of Medicago saliva, thus the development of shrub-grass belts is a main way to develop animal husbandry and to enlarge forage and fodder supplies in desert area.

 

3.2 Larger-scale stem windbreaks and sandbreaks at the periphery of the oasis

At the periphory of oases, the irrigation condition and moiosture condition are available, some high trees with the high sand prevention capability such as Populus euphratica, P. bolleana, Ulmus pumila and Elaeagnus oxycarpa, are widely planted; the most of forest belt width is more than 20-30 m, which could reduce 40-50% of wind velocity within the protective range of 10-15 times of the tree height on the lee side.

At some oasis periphery without the establishment of shrub-grass belts, the plantation of stem shelterbelts plays an important role in preventing the mobile dunes from sand invasion and accumulations around the oasis. But, the different belts with different structure have the different function to fix sands, and they are related to the component of tree species, belt width, and the angle between the belt and wind direction, whether the sand sources is rich or not, etc. Inside the shelterbelt with close structure, moving sands begin to be accumulated in the edge area of shelterbelt on the windward side, to form high, large longitudinal dunes, the mean annual accumulation of sand around the shelterbelt is 12.48 m3 /m; in the shelterbelt with ventilate structure, sands begin to be accumulated on the location of 3-4H on the leeward side, to form long and flat longitudinal dunes, the mean annual sand accumulation around the shelterbelt could reach 9.1 m3 per metre; in the shelterbelts with sparse structure, both site of the sand accumulation and the height of longitudinal dunes are characterized by structures of the two shelterbelts stated as above, the mean annual sand accumulation is 11.25 m3/m.

In order to save more irrigation water and reduce the investment for reafforestation, a establishment of narrow belt consisting of two rows of Tamarisk spp. and Elaeagnus oxycarpa, and 3-4 belts (the width between belts is 10-15H) of narrow belts model of shelterbelts arrangement has been developed. Because of the reduction of wind velocity and the increase of roughness, the shelterbelts could prevent the oasis from sand invasion and stablize the mobile dunes (Table 1).

 

3.3 Farmland protective network inside the oasis

Farmland protective shelterbelts composed of narrow shelterbelt of 4-6 rows, which is adopted extensively in Xinjiang, is the main body of protective forest system. In the forest network system, the different forest belts with different structures still keep their own characters of windbreak function, its protective function is closely related to the optimum width between stem belts (Table 2).

 

Table 1. The function of multi-layer of shelterbelt to prevent oasis and stablize dunes

 

 

Belt arrangement

 

Item

1st

2nd

3rd

% of wind velocity between belts for comparison(6.801×10-3)

58.2

54.3

44.1

comprehensive roughness

7.85

13.58

18.13

accumulated sands

m3/m shelterbelt

31.08

4.8

2.14

Accumulated sands

% to the total

81.7

12.7

5.6

 

Table 2. Wind velocity in the shelterbelts with different widths between stem belts

width between core belts

70/10

92/14.2

175/21.8

250/31.3

400/35

wind velocity reduced averagely(%)

52.8

50.2

38.4

29.6

25.0

 

Thus, Xinjiang has extensively adopted the measure of reducing the width between core belts to enhance the functions of the shelterbelts resisting disasters and protecting farmlands. In the area with serious wind and sand disasters and the border districts of the oasis, the width between core belts is 15-20H in general, in the area with slight wind and sand disasters and the interior of the oasis, the width between core belts is 25-30H, so as to form a small shelterbelts system for protecting farmland.

The biological drainage function of shelterbelts has become an important step in the integrated soil improvement in Xinjiang, and more attentions have been paid to the issue. In Anjihai irrigation region of the northern part of Xinjiang, the effective scale of biological drainage of the 9-12 rows of shelterbelts is mainly consisted of P. bolleana and Salix alba and they could reach 100-125 m in general, the ground water level in farmland could be declined by 20-70 cm, the salt concentration in the topsoil could be reduced, at the site of 5H the gross salt could be reduced by 47.2%, at the site of 10H it could be reduced by 37.2%.

Located in Yangdaman Township, Shule County, Southern Xinjiang near the Kashigeer River, the cultivated land of 446.7 ha of the fourth village was divided into 96 pieces of strip-shaped cropping fields, around every small pieces of the cropping fields, 1-2 rows of Elaeagnus Oxycarpa have been planted. After 6-7 years, the ground water level in the farmland has reduced from 1 m to about 2 m, and the salty area in the farmland has been reduced from 50% to nearly 20%.

The better ecological benefit of the farmland protective shelterbelt has promoted the increase of crop production. In the areas with serious wind and sand disasters, wheat yield increased by 16-29%, cotton production increased by 24%; in the area with salinized soil, wheat yield increased by 22.3-47.9%.

In addition, shelterbelts protecting farmland also supply a great deal of timber and other by-products of forest. Taking Shule County,which is one of the advanced counties in tree plantation, as an example, the conserved areas of tree plantation is 2.18×104km2, the living timber storage is 148×104m3, among which the forest belts protecting farmland mainly consisting of P. bolleana occupies above 90% of the total timber storage, the annual regeneration felling is about 3×104m3. When the P.bolleana is regenerated after it has grown for 15 years, the annual net income is 6.8 RMB Yuan per one RMB Yuan investment, the highest can reach 10.96 RMB Yuan during the 21 years from 1964 to 1984, the total forestry investment is 39.18 million RMB Yuan, the total output value is 163.00 million RMB Yuan, the income per capita in countryside is 304.85 RMB Yuan, which play an important role in rural development.

 

3.4 Mixed plant between agriculture and forestry in the inner part of the forest belts

In order to utilize the valuable water-land, light-heat natural resources of the desert and oases, in the sub-lateral canal with the intervals of 36-50 m in the inner part of the forest belts to plant high-effective economic species of trees. Taking Marus spp. as an example, it makes the forest coverage in the farmland increase about 6%, the wind velocity decrease 26.9%, other factors of micro climate be improved obviously, the ecological environment of farmland be optimized further more. Because of the increment of the leaf area coefficient and repeated utilization of water-land resources, the utilization rate of the solar energy has increased 0.09%, the energy transfer rate has increased 15%, the water consumption for one kilograms wheat and maize has decreased 14.6-22.8%.

 

3.5 Windbreaks and sandbreaks

In order to fix the odd pieces of sand land with small scale so as to control sand sources, the kinds of trees such as Elaeagnus oxycarpa with stronger compressive wind erosion and sand burying, and Tamarix spp. which have the higher resistance, by means of drawn water, dragged sand, and level land to build forests. After 2-3 years of afforestation the height of trees can reach 1.5-3m, which can play a function of windbreak and sand-fixed, the roughness can be enhanced from 0.082 cm in bare land to 37.3250 cm in the inner part of forest. But, the sand fixed effect of forest within some scale is closely related to the strength of local large wind and plant coverage (Table 3). Thus, under the prerequisite of maintaining the water equilibrium and forest stability, should do ones best to enhance the plant coverage.

 

3.6 energy and fodder plantations at the periphery of oasis

Fuel energy and fodder plantations have been developed and evolved from the establishment of single fuelwood forest. Productively, the extensively adopted species of trees are Elaeagnus oxycarpa and Hippophae rhamnoides which have stronger salt-resistance, germination, and better effect for improving soil, and high nutritive value.

 
Table 3. Estimation of theoretical value of sand-drifting wind
Inside the shelterbelt with different plant coverage

Coverage(%)

wind velocity

55

110

115

220

225

330

 

35

440

 

50

 

660

770

880

height at 2 m above ground

55.5

66.1

66.7

77.4

88.2

99.1

110.0

111.0

113.5

116.7

220.0

224.4

wind velocity in observation

66.4

77.1

77.8

88.6

99.5

110.5

111.6

112.8

115.6

119.0

223.2

228.3

 

wind scale

44

44

44

55

55

55

66

66

77

88

99

110

 

Since Yangdaman Township of Shule County completed the establishment of shelterbelts in farmland in 1972, by 1984, about 3,020.3 ha Of energy and fodder plantation have been planted on the bog soil and salinized meadowland which was mainly consisted of Elaeagnus Oxycarpa. Research result shows that, one tree of Elaeagnus Oxycarpa at the age of 4-9 years has the annual transpiration of 20.7-26.8 m3, and the ground water level was reduced from original 0.4-0.8 m to 1.5m, and the obvious salt washing process was taken place. In the forest with the age of 3-4 years, total salt in a depth of 0-100 cm topsoil has been reduced by 27.8% than that beyond the forest, and that in the soil under the shelterbelt with a growth of 6-7 years has been reduced by 79.3%. In the forest land of Elaeagnus Oxycarpa with the age of 13 years, there are 67.4 root nodules/m2 on average, adding the decomposition of withered materials, so the soil organic matter has increased 86%, the content of total N has increased 2.6% (Liu Jin, 1987).

The Elaeagnus oxycarpa forest after 3-4 years since it was planted, by means of pruning and felling and so on, the annual fuel output is 4.82t/km2 on average, the annual total fuel output is 4557.8t, its output value can reach 1.455 million RMB Yuan (RMB Yuan/t), adding family plot of 0.75 km2 per family, to make the fuel enough and to spare.

The leaf and fruit of Elaeagnus oxycarpa has rich nourishment, the domestic animals become fat easily after they eat them. The forest of Elaeagnus oxycarpa with the age of 3-8 years, the mean annual fresh leaf output is 5,119.5 kg/ha, the fresh fruit is 947.3 kg/ha; simultaneously, because of the irrigation in the interior of forest, to promote the herb growth, the annual fresh grass output is about 3,000 kg/ha/yr, forestland can provide fodder of 11.3 days for about 200 sheep.

In closed forest on the whole, in summer the wind velocity can lower about 80%, the mean daily temperature lowers 1.7-1.9℃, the maximum temperature lowers 2.4-2.5℃, the ground temperature lowers 3.8℃, the evaporation from water area reduces 22.2%, all of which create better ecological environment conditions for herding domestic animals. Since Yangdaman township finished forest network in farm land and the construction of large scale fuel-herd forest, the disasters such as wind-sand, and salinization have decreased, the soil conditions of cultivated land have been bettered obviously, and provided better conditions for herding domestic animals near the farmlands. The amount of livestock on hand is more than 42 thousand (increase 4.2 times than that in 1972), the mean weight of sheep has increased from 15 kg to above 20 kg; the amount of applying fertilizer has increased from 60t/km2 of crude mixed fertilizer to 1,462t/km2 of high-quality fertilizer, the per unit area yield has enhanced to 7.23t/km2 (6.4 times), which make the agriculture production that is in the state of vicious circle transform to the direction of ecological agriculture.

 

4 Conclusion

 

Through studies and practices for many years, Xinjiang has found out a set of the models of construction of oasis shelterbelt system in the regions with serious wind-sand disasters, which play a very important role for the oasis stability and the development of the production of agriculture and animal husbandry. We point out emphatically that: after one oasis with a certain scale has finished the construction of shelterbelt system, because the forests and trees are distributed evenly in the whole oasis, the roughness has increased, the reflection rate has decreased, as well as the forest transpiration has enhanced the vapor concentration which make the local climate transform to the direction favorable for human production and human live, and bring about obvious effect to preventing desertification, because of paper length limitation pardon me for not stating.

 

Literature recited

 

1.         Ci Longjun, Construction of protection forest system in Xinjiang, Xinjiang people press, 1980. (P44-48)

2.         Liu Guangzong, Preliminary study on forage value of some xerophytes. Xinjiang forestry science, 1985, (4)

3.         Liu Jin, Preliminary survey and study on the ecological and economic benefit of fuel-herd forest in Yangdaman township. Xinjiang forestry science, No.1, 1987.