| Cropland is the basic means of production for human survival,and it is also the largest human-made landscape in all types of land use.Cropland expansion refers to the process of converting natural vegetation(such as forests and grasslands)into cropland,which is one of the most significant land use changes.With the continuous increase of world population,the demand for food,feed,fuel and raw materials is growing,the competition for land and natural resources is intensifying,and the area of cultivated land is continuing to expand.Over the past two decades,the global cropland area has increased by 16%,and this trend is more pronounced in developing countries.Most developing economies,and the majority of the populations living within them,depend directly on land and natural resources,which in turn leads to the expansion of cropland.As the largest developing country in the world,although China is experiencing rapid urbanization and the expansion of construction land,which has led to the loss of cropland in some eastern regions,but in the northwest and southwest regions with fewer cropland resources,the area of cropland is still showing a significant increase,especially in the Tibetan Plateau region.In recent years,with the rapid economic development and the increasing population in the Tibetan Plateau,the demand for the cropland is also increasing.And due to the impact of global climate change,the trend of continuous warming in the region is evident,which leads to the improvement of heat resources,and consequently the cropland area has continued to increase,extending to higher altitudes.The increased cropland mainly derives from grassland.According to existing researches,the total area of cropland in the Tibetan Plateau has been on an upward trend since the1950s,and from 1950 to 1980,the total area of cropland in Qinghai Province and Tibet Autonomous Region increased by 49.84%.After that,although the impact of the project of returning cropland to forests and grassland has reduced the amount of cropland,but the area of cropland in the Tibet Autonomous Region continued to increase by 13.87%from 1980 to 2010.However,the Tibetan Plateau region is the"River Source"and"Water Tower"of China and even Asia,and it is also an important barrier for the stability of China’s climate system with East Asia,which is very sensitive to global climate change and human intervention response as a typical high-altitude ecological fragile area.Although the cropland expansion in the region helps to increase food production and alleviate the pressure on food demand to a certain extent,it will also cause irreversible damage to the original ecosystem,threaten biodiversity in the region,cause grassland degradation and desertification.Therefore,it is necessary to adopt remote sensing technology for real-time and dynamic monitoring of cropland in the Tibetan Plateau to determine its change characteristics,so as to ensure the regional food security and ecological environment security.At the same time,it is necessary to clarify the influencing factors of cropland expansion in the Tibetan Plateau,so as to take appropriate measures to intervene and adapt to the cropland expansion process,which aims to support rational land use and balance the ecosystem services.The process of cropland change is complex and takes place on different pathways,with varying magnitudes and rates,and the driving factors of cropland change on different scales are different.Existing researches have tried to explain the reasons for the cropland changes from topographical factors(elevation,slope,soil type),climate factors(temperature,precipitation),socioeconomic factors(population density,foreign labor migration),neighborhood factors(distance to the road,river,and town)at the regional or plot level.However,from the perspective of households,in the TP,where cropland accounts for a small proportion,as the most basic socio-economic unit and the main decision-making body,households’cropland use decision can also have a non-ignorable impact on the change of cropland,but few studies have paid attention to this.Based on this,the Pumqu River Basin,a typical high altitude vulnerable area in the Tibetan Plateau,was selected as the research area.Firstly,through the interpretation of remote sensing images,the current situation and characteristics of the cropland expansion of the Pumqu River Basin are determined.Then,based on the 683 household questionnaires obtained in the region from July to August 2018,the influencing factors of the cropland reclamation of the household are quantitatively analyzed through the econometric model.This study aimed to determine the changes of cropland on the Pumqu River basin in the past decade,and clarify the influencing factors of cropland reclamation at the household level,provide a scientific basis for regional ecological environmental protection and sustainable development of households’livelihood,and present a reference for researches on other regions.The specific research results are as follows:(1)According to the visual interpretation of 10 Landsat TM/OLI images of the Pumqu River Basin in 2008 and 2018,the cropland area of the Pumqu River Basin in 2008 was 173.42 km~2,and177.37 km~2 in 2018.In the past 10 years,the area of cropland in the Pumqu River Basin had increased by 3.95 km~2,and the actual newly increased cropland area was 5.83 km~2,accounting for3.36%of the cropland area in the Pumqu River Basin;during this period,the area of cropland had decreased by 1.88 km~2,mainly due to the expansion of urban construction land.By analyzing the relationship between the cropland expansion and elevation,slope,climate,etc.,it was found that the newly increased cropland was mostly distributed in the area between the elevation of4100-4600 m and the slope of 5-10.There was a significant correlation between the increase of temperature and the cropland expansion,while there was no significant correlation between the fluctuation change of precipitation and the change of cropland.(2)According to the analysis of 683 household questionnaires in the Pengqu River Basin,although households’perception of climate change was not necessarily consistent with the measured data,their perception of climate change was still a key factor affecting their adaptation behavior.The local households generally perceived the increase of temperature,precipitation and drought.The perception of temperature had a significant positive impact on their cropland reclamation decision,and the perception of drought has a significant negative impact on their cropland reclamation decision.That is to say,when households perceived the rise of temperature,they were inclined to reclaim farmland,but when they perceived the increase of drought disaster,they would not reclaim new cropland.However,the perception of precipitation had no significant effect on cropland reclamation,which might be the result of the high coverage of irrigation facilities in the basin.(3)The households’non-agricultural development displayed a negative effect on their cropland reclamation behavior.Both the proportion of labor force going out to work and the annual non-agricultural income per capita had a significant negative impact on their cropland reclamation decision.Households with better non-agricultural development conditions were more inclined to livelihood non-agriculturalization rather than reclaiming new cropland.(4)Population pressure and household agricultural production inputs all significantly positively affected households’cropland reclamation decision.The households with large household size had a greater demand for food,and thus the reclamation of cropland had become a vital means to alleviate the contradiction between population pressure and food demand.Similarly,the households who had invested more in agricultural production might rely more on cropland and agriculture,so that they would reclaim new cropland.(5)In addition,the proportion of family members in good health,dependency ratio,and agricultural machinery had a significant positive impact on the cropland reclamation.It was not difficult to understand that the households with a low proportion of family members in good health lacked sufficient labor force for reclamation,and the households with high dependency ratio were inclined to reclaim new cropland for they need more food.The households who had more agricultural machinery were equivalent to more agricultural labor force,so they tend to reclaim cropland. |
