The Research On Landscape Evolution And Its Driving Factors Of Dry-hot Valley In Yuan Iiang River

The dry-hot valley of Yuanjiang river is the most typical dry-hot valley in China with the most serious environmental problems and prominent contradictions between plowland and human.Serious environmental problems result in the changes of regional landscape patterns,which will further aggravate environmental problems and affect regional sustainable development.Based on the data of land use remote sensing image in 2000,2010 and 2015,DEM elevation data,1:750000 soil data,meteorological station data and socio-economic statistics,we studied the spatial distribution characteristics of landscape,the change process,the change trends and its driving forces of landscape changes in Yuanjiang river dry-hot valley,the main conclusions are as follows:(1)The spatial distribution chatacteristics of landscape in the three periods showed same trends:grassland is the dominant landscape type and accounts for more than 50%of the total study area,the rest are woodland,farmland,water area,and urban constructions.The grassland is mainly distributed at an altitude from 500m to 1000m and the slope is above 25 ° in study area.The woodland is mainly distributed in the northwest and middle areas and at an altitude between 1000m and 2280m,the slope is above 15° in study area.The most important distribution area of farmland is between 500m and 1000m above sea level and the slope is between 15 ° and 25 °.The urban construction is related to altitude and slope closely,most of it distributed in the low altitude under 500 m and the slope less than 5 ° of the valley area.(2)From the landscape structure change,the grassland is the largest increase landscape type in the past 15 years,followed by urban construction,and the woodland reduce the most,followed by farmland.From landscape change dynamic degree,the largest annual change rate of urban construction indicated that the urban construction change fastest,followed by woodland and farmland.From the frequency of landscape changes,most of the study area have no landscape change,small part have landscape change.From the spatial distribution of landscape changes,the landscape change mainly occurred in the low slope area between 15 °?30 ° slope between the steep area except the farmland change to urban construction occurred in the valley area,and dry red soil and purple soil because of its low soil productivity,more prone to landscape changes.(3)The results of landscape shape index analysis showed that the increasing trend of landscape shape index of all landscape type level and landscape level illustrated that the patch shape was tend to be irregular and complex in the past 15 years.The increasing patch edge density index and the decreasing aggregation index indicated that the landscape pattern became fragment gradually.The Shannon diversity index and evenness index showed a same trend that they would decrease first and then start to increase,which showed that the dominance of grassland increased and then decreased in the whole research period.(4)During the period from 2000 to 2010,the change of farmland and woodland were mainly affected by the total grain output and total population.Temperature and rainfall have a great influence on the change of farmland,and the development of social economy play a majorr role in the forestland change.From 2010 to 2015,social population,such as agricultural population,became the main driving force of the farmland change and the woodland change.Different from farmland and woodland,the change of grassland is small,and the economic development level is the main factor in both periods.The temperature and rainfall factors play an important role in the evolution of grassland landscape.(5)According to the comprehensive analysis,the social and economic development is the key driving factor of the landscape evolution in study area.With the increasing proportion of the secondary industry and tertiary industry and decreasing proportion of the primary industry,non-agricultural population increased quickly,town area and the mining land increased fast.In addition,the change of temperature and rainfall played an important role in landscape evolution in study area.Under the background of the rising temperature and decreasing rainfall in the southwest,the change of temperature and rainfall in the dry-hot valley is especially prominent.Because of its special environment and fragile ecosystem,the driving effect of temperature and rainfall on the landscape in dry-hot valley is significantly greater.