Spatiotemporal Dynamics and Drivers of Farmland Changes in Panxi Mountainous Region, China
Due to the multiple impacts of landform effects, spatial heterogeneity and land use policies, farmland dynamics in mountainous areas are complicated. This study investigated farmland dynamics based on land use data from a typical mountainous area, Panxi, in China for 1990China for , 2000 and 2010, discussed the relationship between altitude, slope and farmland changes and presented an analysis of the driving forces of farmland change. Our findings are as follows: (1) from 1990 to 2010, the area
... 0 to 2010, the area of converted farmland was relatively small (313 km 2 ), accounting for only 2.6% of the region's farmland. Farmland was mainly converted to forest and grassland as a result of the Returning Farmland to Forest Program; (2) The spatial distribution of land use types differed significantly. The presence of water bodies influenced farmland and built-up land, while forest and grassland showed "landform-oriented" characteristics. Built-up land was especially variable in distribution, indicating that it was more vulnerable to human activities; (3) The vertical differentiation of farmland changes was obvious. At altitudes <2500 m, the data displayed a trend of conversion from forest to farmland, while at >2500 m, this trend reversed. Thus, 2500 m serves as an altitudinal boundary between farmland and forest in Panxi. The largest area of forest-farmland transfer occurred on slopes steeper than 15 • , not 25 • , as defined by China's policy of Returning Farmland to Forest; (4) The driving forces of farmland changes varied. Decreases in farmland were negatively correlated with proximity to rivers and roads. Increases in farmland were positively related to temperature and negatively related to both population density and altitude. farmland by 500,000 hectares, which approaches the total area of France, Germany and the U.K., profoundly affecting the overall ecological statues of European ecosystems  . Under the guidance of the EU, agri-environment schemes (AES) and other funding mechanisms have been implemented under the CAP to achieve nature-friendly management and ecological farming  . Following these important measures, many others have been implemented, laying a foundation for sustainable development in other countries. As China has experienced rapid urbanization, industrialization and economic development, China's farmland has changed significantly. According to the 2008 Bulletin of National Land and Resources data, since 1996, China's farmland has decreased by 8.3 million hm 2 , or 595.24 thousand hm 2 per year  . Nonetheless, agriculture is very important in China, and a large population requires food produced by farmland to maintain life; thus, the limited farmland resources are experiencing production pressure  . Furthermore, due to unplanned land use, a series of ecological environmental problems, such as water pollution, air pollution and soil erosion, took place in the process of urbanization [14, 15] . Tension between food security, ecological protection and economic development has become intense. China's central government has implemented policies to address the contradiction, and the dynamic change of farmland and its driving forces have attracted the attention of scholars. However, most of these study areas focused on the development of nations, provinces and urban agglomeration. Only a limited number of studies have focused on less-developed regions or ecologically-fragile, mountainous areas  . In China, mountainous areas account for 70% of the total land area with almost 40% of the population  . Mountainous areas are therefore important for land use and population studies. As a result of geographical and soil conditions, farmland is not prevalent in China's mountainous areas. In fact, farmland accounts for less than 15% of the land in China's mountainous areas. The soil quality is not very high  , and food from such limited farmland cannot meet the demands of the population. Importantly, the ecology in mountainous areas is often fragile: once destroyed, it is difficult to recover. Since the acceleration of urbanization, a large amount of farmland in China has been converted into other land use types, creating ecological threats. Therefore, there is a pressing need to manage farmland change and its effects on natural environments, particularly in ecologically-fragile mountainous regions. Recently, a wide variety of researchers has modeled spatiotemporal patterns of farmland conversion, investigated the causes of farmland conversion and analyzed the impacts of land use change     . Until now, there have been two main methods used to describe the characteristics of farmland change: the landscape index  and spatial statistics  . These two methods are based on remote sensing data. Remote sensing (RS) has been recognized as a powerful and effective tool for detecting the spatiotemporal dynamics of land use, and spatially-explicit time series of land use change can be developed based on RS . Forecasting trends in farmland change has mainly included the development of a simple Markov chain model and the Conversion of Land Use and its Effects at small regional extent (CLUE-s) model [26, 27] . These two models have been of great value to policymakers in predicting farmland changes and making informed decisions about such changes. Of course, various forces influence farmland change, such as national policy, population change, economy, science and technology, per capita income, agricultural production, land use policy, topography and natural disasters. These forces can be broadly divided into physical and anthropogenic categories. Physical drivers include climate , terrain , soil , hydrology and locust hazard . These physical forces can result in reduced agricultural harvests and food shortages, even large numbers of deaths. Anthropogenic drivers include the economy, population, agricultural modernization , technology , culture , agricultural policies  and food regimes  . Farmland changes, while restricted by physical conditions, are mainly driven by anthropogenic factors and characterized by changes in built-up land and forest, both of which are closely related to human production activities and national policy  .