The Great Transition: Long-term ecological changes in China's ancient village landscapes

Background/Question/Methods:  Densely populated agricultural villages cover more than 2 million square kilometers across China’s eastern plains and central and southern hilly regions.  This vast extent of ancient anthropogenic landscapes has been transformed over the past fifty years by unprecedented changes in population, social structure and technology.  Most of these changes have occurred at very fine spatial scales driven by the activities of hundreds of millions of rural households.  The long-term biogeochemical consequences of these changes were investigated using high-resolution field measurements and historical reconstruction of landscape structure, resource management, and biogeochemical parameters circa 1945 to 2002 across China’s densely populated village landscapes using a regional sampling and upscaling approach.  

Results/Conclusions: As expected, landscapes became increasingly fragmented over time, largely as a result of increases in built structures, yielding a net increase in impervious surface area similar in magnitude to the total current extent of China’s cities.  Surprisingly, woody vegetation and tree cover also increased over time in these same areas, by approximately 10%, driven by the introduction of perennial agriculture and improved forestry practices, tree planting and regrowth around new buildings and the abandonment of a substantial area of annual cropland.  Increased cover by perennial vegetation indicates that village landscapes have likely served as carbon sinks over the past fifty years, while agricultural intensification on the smaller area of remaining croplands has likely increased nitrogen emissions to the atmosphere. These observations demonstrate that fine-scale changes within anthropogenic landscapes have the potential to contribute substantially and in unforeseen ways to global changes in biogeochemistry and climate.