The expansion of agricultural area and the increase of agricultural land intensity have led to a series of environmental problems, such as the destruction of forests, the retreat and disappearance of natural landscapes such as water and wetlands, the intensification of land degradation and soil erosion, and the reduction or even extinction of animal and plant populations. Agriculture not only reshapes the landscape pattern, but also affects the regional and global climate.
In the period of primitive agriculture, human beings mainly adapted to the natural environment, and land development was mainly concentrated in relatively flat areas, and the changes to vegetation were mostly partial. The changes in vegetation region caused by agricultural production activities can be found in the sporopollen records near some archaeological sites.
During the Warring States period, highland, flat land and depression were all developed, but the development of Potuo land and depression was mainly near residential areas, while mountains and Zhaze were mainly places where people collected, fished and hunted, and most areas were still vast and sparsely populated. After Qin and Han Dynasties, the sequence of cultivated land reclamation and expansion in China is generally from the northern region to the southern region, from the plain lowlands to the low mountains and hills, and then to the deep mountains, and the process of vegetation destruction corresponds to this.
Most of the arable grasslands and woodlands in the northern agricultural areas were reclaimed in the Western Han Dynasty, and a large number of forests were reclaimed as farmland in the late Hanzhong period, so that the government could no longer distribute public woodlands and imperial houses to landless refugees as in the early Hanzhong period. During the Song and Jin Dynasties, there were no natural forests in Guanzhong Plain and Fensu River Basin, and the vegetation in loess hilly areas was also destroyed. By the Qing dynasty, not only the flat land in the northern region was completely reclaimed, but also some hilly and gully areas with steep slopes were reclaimed. Since the late Qing Dynasty, agricultural reclamation has spread to the northeast and Inner Mongolia outside the Great Wall, and the grasslands and woodlands in the northeast have been destroyed with the rapid advancement of cultivated land to the north and the rapid increase of area.
From the end of the Warring States Period to the Han, Wei and Six Dynasties, "Fire Farming and Water Weaving" was still widely popular in southern rice farming areas. The development of the south of the Yangtze River mainly occurred after the Tang and Song Dynasties, which was closely related to the large-scale southward migration of the northern population. The development sequence is generally from plain lowlands to low mountains and hills, and then to deep mountains. Since the end of the Eastern Han Dynasty, agricultural reclamation activities have been carried out in the hilly areas of Sichuan Basin. By the middle of the Southern Song Dynasty, the Zhongshan area around the basin had begun to cultivate agricultural land.
In order to curb the problem of soil erosion in mountainous areas caused by slope development, a small number of terraces appeared in Pengshui, Chongqing in the Eastern Han Dynasty. The rapid development of terraced fields in the Tang and Song Dynasties further accelerated the development of mountainous areas, and the hills and low mountainous areas in the Yangtze River basin showed obvious agricultural landscape in the Southern Song Dynasty. In the Ming Dynasty, there were not many natural forests in hilly and low mountain areas of the Yangtze River basin, but in the middle and high mountain areas, the original forest vegetation did not change.
By the Qing dynasty, especially after the middle of the Qing dynasty, the southern mountainous areas were reclaimed on a large scale. For example, in the early Qing Dynasty, reclamation and deforestation in Sichuan Basin were mainly confined to the hillside and below the foot of the hillside (about 800 ~ 1500 im above sea level), while in the middle Qing Dynasty, it was promoted to the top of the mountain and the upper half of the mountain (about 1000 ~ 2000im above sea level) and around the basin.