| As an important part of ecological system,the land can provide indispensable physical basis for human survival and the development of social economy.As human activities take place in the land,a variety of structures of land utilization have been formed.Different structures of land utilization will necessarily have a considerable influence on the regional ecological environment.Under natural condition,there is a dynamic balance between soil erosion and soil formation.However,because of the influence and interference of human activities,the irrational structure of land utilization has changed the regional terrain,damaged the vegetation resource on the surface and also undermined the soil quality.As a result,the deterioration and movement of surface soil caused by natural factors have been accelerating and far outpacing the process of soil formation.Moreover,it has also accelerated the water and soil loss,further worsening the soil erosion in the local area.Under the relatively stable natural condition,land utilization has become a main factor influencing the process of soil erosion.Therefore,the adjustment and optimization of the existing structure of land utilization has become the key to controlling soil erosion.In recent years,great efforts have been made to build the artificial economic gardens with eucalyptus and rubber trees on a large scale in Lancang County.They have replaced the cultivated land or various lands(including the secondary evergreen broad-leaved forest,pinus kesiya,shrub forest and unused grassland)with the same area.With the implementation of the 12th Five-year Plan and the release of the 13th Five-year plan,there is a growing demand for the construction land.It also has a potential effect on the regional ecological environment,especially the conservation of water and soil.Hence,based on the analysis on the features of the change in soil erosion,this paper has pointed out the necessity of optimizing the structure of land utilization from the perspective of controlling the soil erosion.It is not only of great importance to the control over soil erosion in Lancang County but also becomes a key to realizing the sustainable development in the county.With the purpose of optimizing the social benefit,economic benefit and the control over the quantity of soil erosion,this research has set a constraint on the total quantity of soil erosion,total land area,total population,cultivated land,total construction land,other macro-factors and mathematical model.What is more,the model of Grey Multi-Goal and Dynamic Programming(GMDP)has been built to realize the optimal allocation of quantitative structure of land utilization in Lancang County for the years of 2020 and 2025.The optimization scheme will be also compared with the Overall Plan for Land Utilization in Lahu Autonomous County of Lancang from 2010 to 2020(hereinafter referred to as the Overall Plan)and the current status of land utilization.The main conclusions of this paper are as follows.(1)With the purpose of optimizing the social benefit,economic benefit and the control over the quantity of soil erosion,this research has set a constraint on the total quantity of soil erosion,total land area,total population,cultivated land,total construction land,other macro-factors and mathematical model.What is more,the model of Grey Multi-Goal and Dynamic Programming(GMDP)has been built to realize the optimal allocation of quantitative structure of land utilization in Lancang County for the years of 2020 and 2025.The optimization scheme will be also compared with the Overall Plan for Land Utilization in Lahu Autonomous County of Lancang from 2010 to 2020(hereinafter referred to as the Overall Plan)and the current status of land utilization.The main conclusions of this paper are as follows.(2)From 2000 to 2005,the area of cultivated land,shrub forest and nature reserve was shrinking.In contrast,the forest land was gaining in area.From 2005 to 2010,the area of cultivated land,shrub forest and nature reserve was decreasing.The area of the land for other uses,especially eucalyptus forest,was on the increase.From 2010 to 2015,the area of the land for water body,eucalyptus forest,forest land and construction land was increasing while the area of cultivated land,garden land,shrub forest and nature reserve was on the decrease.The land for eucalyptus forest was mainly reclaimed from the cultivated land,forest land and nature reserve.With regard to the change in the intensity of soil erosion,the area of the land with soil subject to severe and highly intensive corrosion was obviously decreasing from 2000 to 2010.There was also a shift towards the soil erosion at the minor,slight or modest level.From 2010 to 2015,the area of soil erosion at the intensive and severe level was reduced.There was an unobvious shift towards the erosion at the minor,slight or modest level.From the perspective of the spatial distribution of soil erosion,the severe soil erosion is mainly concentrated in the northern part,southern part and central part of Lancang County.To be more specific,those towns and villages in the central area of river valley and the northern part of the county were suffering from serious soil erosion.Moreover,the soil erosion in those towns and villages in the southern area remained at a modest level.It is found that there is a relationship between the change of land utilization and the changing intensity of soil erosion.During the 15 years,the intensity of soil erosion would increase with the cultivated land changed into the nature reserve and the forest land changed into the cultivated land.In addition,the intensity of soil erosion would decrease with the cultivated land changed into the forest land or eucalyptus forest,shrub forest changed into the eucalyptus forest or forest land as well as the nature reserve changed into the forest land.(3)With the society,economy and minimum quantity of soil erosion chosen in thetarget function,the model of Grey Multi-Goal and Dynamic Programming(GMDP)has been built to optimize the structure of land utilization for the years of 2020 and 2025.For the year of 2020,four optimization schemes aimed at maximizing the social and economic benefit as well as controlling the quantity of soil erosion have been proposed.The comparison with the Overall Plan has been also made.?For the four optimization schemes,all of them can improve the social and economic benefits compared with the current status.Moreover,the quantity of soil erosion can be also reduced by 890.49×104 t,515.33×104 t,567.25×104 t and 572.28x 104t respectively.Compared with the Overall Plan,the second,third and fourth scheme can achieve better social and economic benefits.But the first scheme has been outperformed by the Overall Plan in terms of social and economic benefit.In addition,the quantity of soil erosion in the four schemes is lower than that of the Overall Plan.Compared with the Overall Plan,it can be reduced by 801.42×1 04 t,426.26×104 t,477.85×104 t and 483.21×104 t respectively.It can be seen that the first scheme has performed best for controlling the soil erosion.?The area of cultivated land in the four schemes is smaller than what is required in the Overall Plan.The second,third and fourth scheme have also exceeded the quantity of cultivated land for Lancang County in the 13th Five-year plan.The area of garden land in the third and fourth scheme has increased.The area of grassland in the four schemes remains at a stable level.The area of forest land in the first,third and fourth scheme is larger than that of the Overall Plan.After the optimization,the area of eucalyptus forest has increased.The area of construction land in the four schemes is smaller than that of the Overall Plan The area of water body for the four schemes is consistent with that of the Overall Plan.The area of nature reserve is slightly smaller than that in the Overall Plan.Among the four schemes,the fourth scheme has achieved the best social and economic benefits.The structure of land utilization has been adjusted to better satisfy the social demand.Moreover,it can also effectively control the soil erosion and achieve the highest population supporting capacity of the land.Hence,the fourth scheme can be chosen as the optimal scheme for the optimization of quantitative structure of land utilization in 2020.(4)The optimization scheme for the year of 2025 can outperform the Overall Plan and current status in terms of social and economic benefits.Compared with the Overall Plan and current status,it can reduce the quantity of soil erosion by 526.32×104 t and 615.39×104 t respectively.In other words,the purpose of reducing the total quantity of soil erosion can be realized.After the optimization,the area of cultivated land per capita is 0.425 hm2/person,exceeding the minimum standard for the area of cultivated land per capita.Besides,the area of cultivated land has reached the minimum standard in the 13th Five-year plan.The total area of forest land amounts to 550322.32 hm2,which exceeds that of the Overall Plan by 2815.78 hm2.The grassland area is basically the same as that of the Overall Plan.The allocation of construction land can satisfy the requirement of the total demand for construction in 2025.The area of water body is consistent with that of the Overall Plan.The area of nature reserve can be reduced accordingly.Some advice has been also proposed in this paper,including maintaining the original structure of forest land in Lancang,introducing the eucalyptus forest scientifically,planning the area of economic garden properly as well as achieving the balance between original forest land and economic forest land.To conclude,those measures can play an important role in the conservation of water and soil in the region. |
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