| Natural rubber is a type of widely used bulk industrial raw material,which is as famous as oil,iron ore and non-ferrous metals in the world.It is an important strategic material required by national defense and economic construction.China is the world’s largest consumer of natural rubber.Since the middle of the last century,China began to explore natural rubber planting areas,and through the unremitting efforts of many generations of scientific researchers,it has built natural rubber planting areas with Xishuangbanna and Hainan at the centers.Due to its unique geographical advantages,Xishuangbanna has become the second largest natural rubber planting base in the northern tropical margin of China,which has made important contributions to the material reserve of natural rubber and related products in China and the promotion of local economic development.However,while bringing economic income,the blind and disorderly expansion of rubber plantation also causes many ecological and environmental problems such as the fragmentation and fragmentation of tropical forests and the destruction of animal and plant habitats,which directly or indirectly leads to the loss of biodiversity and the decline of ecological service value in Xishuangbanna,threatening the ecological security of the northern tropical margin.In addition,Xishuangbanna has a tropical and subtropical monsoon climate,and there is just an upper limit of suitable planting altitude for rubber plantation.If the rubber forest exceeds the apt planting threshold,the rubber yield decreases,the risk of cold damage increases,and the economic and ecological benefits generally decrease.Therefore,scientific determination of the upper limit of suitable planting altitude of rubber forest in Xishuangbanna,and ecological restoration of unsuitable planting areas of rubber forest,to support the ecological environment construction of Xishuangbanna and sustainable development of regional social economy,have become important issues to be solved urgently.Based on Landsat remote sensing data,this study used random forest classifier to extract rubber forests in Xishuangbanna from 2000 to 2020,and dynamically monitored the spatio-temporal variation pattern of rubber forests in Xishuangbanna from 2000 to 2020.Based on climate,terrain and other ecological factors and production performance such as rubber yield,the upper limit of suitable planting altitude of rubber forest in Xishuangbanna was comprehensively identified,and rubber forest in unsuitable planting area was extracted according to the upper limit of suitable planting altitude of rubber forest,and ecological restoration of rubber forest in unsuitable planting area was carried out.In order to provide scientific basis and decision support for the rational layout and regional ecological construction of rubber plantation in Xishuangbanna.The main research results are as following:(1)Temporal and spatial distribution characteristics of rubber forest in Xishuangbanna.The plantation area of rubber forest in Xishuangbanna showed an increasing trend from 2000 to 2020,and the proportion of rubber forest area in the regional land area increased from 12.63% in 2000 to 26.28% in 2020.Rubber forests are mainly distributed in Jinghong City and Mengla County in the south where the water and heat conditions are better.A small amount of rubber forests are also allocated in Menghai County.The rubber plantation area in Xishuangbanna was mainly distributed in the range of 500-1100 m above sea level,showing a trend of expanding from low altitude area to high altitude area.Rubber was mainly planted on gentle slope and steep slope,and rubber plantation was found in the range of slope(> 35°)that was not suitable for planting rubber forest.The overall slope distribution trend of rubber forest was strong in north and south,weak in east and west.The planting area was the least in due east,and gradually expanded from south slope to north slope.On the whole,Xishuangbanna rubber forest continues to expand from low altitude to high sea,low latitude to high latitude,low slope to high slope,south slope to north slope.(2)Determination of the upper limit of suitable planting altitude of rubber forest in Xishuangbanna.The temperature suitability in Xishuangbanna decreased gradually from south to northwest and northeast.The highest precipitation suitability value of Xishuangbanna appeared in Mengla County,followed by Jinghong City,and the lowest value appeared in Menghai.The planting climate suitability of Xishuangbanna rubber forest is 0.08-0.70,and the high suitability area is mainly released during the month of the south of Jinghong City and the northwest of Menghai County.Few areas of Menghai County belong to the high suitability area.Built on the evaluation results of climate suitability and terrain suitability of rubber plantation,the upper limit of suitable planting altitude of rubber plantation in Xishuangbanna was determined to be 870-974 m.According to the statistical analysis of the rubber yield of Paomao Village sample site in Xishuangbanna,the rubber yield decreases with the increase of altitude,and the rubber yield decreases rapidly when the sample site is larger than 950 m,indicating that the upper limit of planting is reasonable.Depending on the upper limit of suitable planting altitude of rubber forest,the rubber forest was extracted from the unsuitable planting area in Xishuangbanna in 2020.The results showed that 23.65% of the existing rubber plantations were released during the month of areas unsuitable for planting.(3)Ecological restoration in unsuitable planting area of rubber forest in Xishuangbanna.Built on the ecological sensitivity of Xishuangbanna,the rubber forest in unsuitable planting area was divided into priority restoration area,important restoration area and potential restoration area.The urgency and importance of restoration were priority restoration area,important restoration area and potential restoration area.The priority restoration area is in the area of high and extremely sensitive ecology,which is characterized by fragile self-restoration ability and difficulty once the ecological environment is damaged.The key point of vegetation restoration is to return glue to forest and establish ecological corridor with nature reserve.The economic value of rubber plantations in significant ecological restoration areas is very low,but the demand for ecological services such as water conservation and water and soil conservation is high.The target of vegetation restoration in this region is tropical rain forest landscape.Artificial assisted restoration methods such as reintroduction of native species are adapted to gradually eliminate rubber trees to restore tropical rain forest and rebuild regional water conservation,soil and water conservation and other ecological service functions.The potential restoration area has minimal ecological sensitivity,so it can be divided into ecological restoration buffer zone to reduce the pressure of ecological restoration.When necessary,it will be reserved as rubber strategic reserve area.The core ideas of restoration are as follows: selective preservation,vigorously developing the combined economy of agriculture,forestry and animal husbandry,and improving the comprehensive benefit of rubber forest. |
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