Environmental history of China

History of the natural environment and human interaction in China From Wikipedia, the free encyclopedia

The environmental history of China examines changes in the natural ecological landscape (environment) throughout Chinese history and the interactive relationship between successive generations of Chinese people and their environment.^[1]^{: 107、104} The degree to which China transformed and utilized nature was almost unmatched in the pre-modern world;^[2]^: 336 the extent of environmental change was likely greater than that caused by any other country in the world, with the basic principle being the development of nature for human use.^[3]^: 28

The overall trend of the ecological environment in Chinese history has been one of continuous deterioration, with the pace of change accelerating over time. The most dramatic changes involved the disappearance of large areas of forest, followed by the reduction and desertification of grasslands, and the shrinkage or complete disappearance of freshwater lakes.^[4]^: 105 As China's population grew, over 3,000 years of reclamation activities increased cultivated land area but caused extensive deforestation, leading to expanded desert areas and reduced lake surfaces, resulting in severe ecological degradation.^[4]^: 2 The Chinese cleared forests and native vegetation, turning hillsides into terraces and valleys into farmland, built dikes and dams, redirected rivers, relocated lakes, and destroyed wildlife habitats for economic development. After such development and transformation, by the Qing dynasty, little "natural" untouched land remained.^[2]^: 333 In the 20th century, the rise of industrialization and consumer culture accelerated changes in the natural environment.^[5]^: 1

From the Spring and Autumn and Warring States periods onward, early Chinese governments protected dwindling forest resources, sometimes to monopolize them. From the Tang to the early Qing, China was the most ecologically resilient and resource-rich country on Earth, and the most ecologically diverse polity.^[6]^: 43–44 During the Tang, forested land gradually became privatized; by the Song, timber shortages emerged in parts of the lower Yangtze and western regions, leading people to begin afforestation. In the past 300 years, China has faced a forest crisis.^[2]^: 91 From the 18th century, severe timber shortages occurred in many regions, including Lingnan; people focused on cultivating fast-growing tree species, sometimes selling immature trees for profit.^[2]^: 90 Artificial afforestation gradually replaced most of the natural forests in southern China over the past millennium.^[7]^: 309 Ancient China originally had many lakes, but later silted up and disappeared from the surface; the surface area of surviving lakes also shrank significantly compared to before.^[4]^: 89

From the mid-Ming onward, due to rapid population growth, the total environmental pressure exerted by the Chinese increased rapidly.^[8]^: 73 During the Ming and Qing dynasties, as population surged, land resource shortages led to widespread reckless reclamation and deforestation, continuously reducing forest and lake areas and causing soil erosion.^[9]^: 49 This ecological degradation led to increased floods and droughts in later historical periods.^[4]^: 123 The most severe period of ecological deterioration in China was during the mid-Qing Qianlong and Jiaqing reigns (1736–1820), when grain yields per mu also declined.^[4]^: 124 The growth of the agricultural population transformed most ecological landscapes into farmland, reducing opportunities to gather wild resources.^[7]^: 318 Agricultural ecosystems are often far simpler than wild ones, generally relying on a few species and thus more vulnerable to droughts, pests, and other disasters.^[7]^: 304 Wherever intensive agriculture advanced, wild animals such as elephants retreated.^[2]^: 89

Prehistory

Before the development of agriculture, people hunted for a living or gathered food from forests, grasslands, or wetlands, with minimal impact on the environment. Hunter-gatherers may have used fire to clear underbrush in forests to allow new grass to grow, attracting deer herds for easier hunting, but the forests themselves remained. About 10,000 years ago, with the expansion of agriculture, forests began to give way to farmland.^[5]^: 1、31 In the early Neolithic, people cultivated millet while also fishing, hunting, and gathering wild plants.^[7]^: 50 Agriculture emerged almost simultaneously in northern and southern China: annual wild rice in the south and two types of millet in the north. Between 8,000 and 7,000 years ago, millet cultivation originated in the semi-arid savanna of the Wei River valley on the Loess Plateau.^[5]^{: 32、41、48} Before agricultural production, the area's original vegetation consisted of forests and grasslands, with about 30% forest cover. The loose, soft nature of loess soil on the Loess Plateau made it easiest to cultivate with primitive tools in early agriculture, so the Loess Plateau became the main region for early human agricultural development.^[4]^: 34、32 In central and southern China, rice grew along riverbanks, ponds, or in freshwater marshes; wild rice was especially abundant around Dongting Lake, gathered by Neolithic people. By 5000 BCE, rice cultivation was widespread in the Yangtze River basin, Taiwan, and southern China, and settled agricultural communities became widespread and established in central and southern China.^[5]^: 35–36

Between 6000 and 5000 BCE, farmers in the Guanzhong region began burning land for cultivation. People did not continuously farm the same plot but cultivated each area for a few years, then left it fallow for several years before burning and replanting. With abundant land resources, villagers could practice long-term fallowing without needing to fertilize fields.^[7]^: 70、79 Agricultural practices spread northward with migrating populations, then eastward into the forested Yellow River basin and North China Plain.^[5]^: 48 Although the population was sparse, humans had already reduced animal diversity on the plains. In the forested mountainous areas west of Guanzhong, animal diversity was clearly higher than on the plains. Large fish became increasingly rare, and villagers shifted from using harpoons to more nets.^[7]^: 72、84 As population grew, people overexploited huntable or gatherable resources, forcing greater reliance on grains. With agricultural development, people learned to cultivate more plants and domesticate more animals.^[7]^: 86、50 Around 6000 BCE, wild boar in the Yellow and Yangtze River basins were domesticated into domestic pigs.^[10]^: 159 Between 5000 and 3000 BCE, during the Yangshao culture period, people in the central Yellow River basin became heavily dependent on domesticated plants and animals. Increasing reliance on domesticated species such as cattle, sheep, and horses allowed exploitation of previously difficult drylands.^[7]^: 75、90 Farmers initially cleared land by burning grass and used stone hoes and spades to turn the soil. As agriculture developed on the Loess Plateau,^[5]^: 42、46 increasing use of fire and tillage led to soil erosion,^[7]^: 94 increasing the sediment load carried by the Yellow River, which in turn raised the riverbed and banks, expanding the flood-prone area of the North China Plain.^[5]^: 46

Settled agriculture required clearing forests for farmland. Increased food supply from farming led to population growth, necessitating more land clearance. Yangshao people gradually developed methods to clear forests and open farmland. Initially, clearing a plot near the village sufficed, but over time, with technological advances and population pressure, more forests were destroyed. Using stone axes to fell trees was time-consuming and laborious, while burning entire forests was uncontrollable and dangerous. People employed a method of girdling individual trees—stripping a ring of bark from the trunk to block water and nutrients from the roots, allowing the tree to wither naturally. This allowed precise removal of specified numbers of trees.^[5]^: 31、49 Villagers cleared most forests around settlements for firewood and cultivation, and wetlands also decreased.^[7]^: 80–81 In the Yangtze River basin and Loess Plateau, two agricultural systems supported growing populations, leaving less pasture for livestock. However, Neolithic farmers never altered the environment on a large scale. By 2000 BCE, there were probably about 1,000 villages in northern China, each generally housing only a few hundred people and occupying small areas,^[5]^: 45、50 leaving ample space for wild plants and animals.^[7]^: 75

Shang dynasty

The Shang dynasty controlled vast territory and had a dense population. Its northwestern boundary roughly coincided with the modern 20-inch (50 cm) isohyet. West and north of this rainfall line were grasslands and deserts unsuitable for cultivation. Shang civilization's territory extended from deciduous broadleaf oak forests southward to the mixed deciduous and subtropical forests of the Yangtze River basin.^[5]^: 56、62 Major crops included two types of millet, rice, and mulberry. They began transforming the North China Plain into farmland, but large forested areas still provided various game.^[5]^: 59–60 Tigers, elephants, and rhinoceroses lived in the forests. Most of northern China remained dense forest, with only small patches of farmland. Approximately 4–5 million people lived on the North China Plain, with grain yields of about one shi per mu, implying that roughly 10,000 square kilometres (4,000 sq mi) to 13,000 square kilometres (5,000 sq mi) of oak forest had been cleared. Cleared land was usually located within forests to facilitate hunting. Around major cities such as Anyang, the surrounding countryside was largely cleared for farmland.^[5]^: 63–65 Shang people cleared forests tree by tree rather than burning entire tracts, to avoid danger and waste fuel.^[5]^: 66 Oracle bone inscriptions also record forest burning, often related to hunting. Burning could clear native vegetation for farming; fires could drive wild animals from forests for easier capture; and burning could drive away birds and beasts, providing safety for cultivators and protecting crops from trampling.^[4]^: 4

The Shang established walled cities and entered the Bronze Age. Bronze casting required burning large quantities of wood for mining, smelting, and casting, greatly affecting the surrounding environment. When forests were exhausted, the mines were abandoned; after copper and tin reached the capital's foundries, even more wood was needed for refining.^[5]^: 53、56 The Shang center was located between the flood-prone plains and the relatively well-drained area near the Taihang Mountains.^[7]^: 131 Capitals frequently relocated because the Shang practiced shifting cultivation; after several years, soil fertility declined and yields dropped. At that time, people lacked good farming tools and could only use ash from burned vegetation as fertilizer. Without plowing with spades or plows, they relied only on the surface layer of fertility. Within a few years, the soil was exhausted, yields declined, and farmers had to migrate to open new fields. This was the long-term fallow system of primitive agriculture.^[4]^: 5–6 The Shang had vast hunting grounds west and south of Mount Tai. Shang people hunted not only gentle game such as deer, foxes, wolves, and badgers but also large animals such as elephants, tigers, and rhinoceroses.^[2]^: 35 In the densely populated lowlands of Henan, farmland and domestic grazing animals gradually occupied the habitats of large mammals, and human herds gradually replaced native animal populations.^[7]^: 138、98 The expansion of domestic herds reduced land available for wild animals, leading to the extinction of aurochs and wild horses, and making the region the first in East Asia where large animals permanently disappeared.^[7]^{: 100、138} By the late 2nd millennium BCE, large wild mammals had largely vanished from the North China lowlands and survived only in sparsely populated surrounding mountainous areas.^[10]^: 169

Zhou dynasty

Western Zhou

The core area of the Western Zhou was the Wei River valley, where dryland agriculture first developed in China. Loess soil was easy to cultivate and could be planted year after year.^[5]^: 84 Zhou agriculture gradually advanced from long-term shifting fallow to short-term rotational fallow on the same land, often using a three-year cycle: fallow for two years, allowing wild grass and shrubs to grow, then burning the secondary vegetation and using its ash as fertilizer before replanting and beginning the next cycle. Most of the burned "forests" at this stage were on flatlands rather than in mountainous areas.^[4]^: 7 The Wei River provided fresh water for the Zhou, while timber for construction and heating came from the Qinling Mountains to the south. Under the feudal system, Zhou people cleared forests to open farmland on enfeoffed lands.^[5]^: 84–85 With walled towns as central points, they burned forest land layer by layer, expanding farmland according to population needs. Beyond the agricultural zone, wild grass and secondary shrubs were allowed to grow as pasture, while the outermost areas remained unburned forest serving as defensive barriers and territorial boundaries.^[4]^: 7 At the same time, the Zhou drove nomadic peoples from the grasslands of the Loess Plateau and opened them for cultivation and farming. When arable land was insufficient, they cleared forests in hilly areas.^[11]^: 84–85

In the early Western Zhou, large areas of uncultivated land still existed on the North China Plain and in the Wei River valley. Forest clearance expanded eastward, northeastward, and northwestward from the Shang core on the North China Plain. The eastern Yellow River alluvial plain was flat and densely forested. Because the Yellow River flooded periodically, the area was originally unsuitable for farming or building cities, so settlements were built on higher ground north and south of the river channel. The Zhou used stone or wooden plows to open land, pulled by human labor or oxen. Loess soil was highly susceptible to erosion, so the Zhou built ridges in fields to reduce soil loss.^[5]^: 85–86 The Zhou did not revere forests and made no effort to protect them.^[2]^: 52 As forests and grasslands disappeared on the Loess Plateau, sediment runoff increased and the Yellow River gradually turned yellow.^[11]^: 85 The Zhou gradually developed the idea that humans should dominate and control nature, that the correct natural order should be governed by humans, and that wild animals should be driven away. By around 1000 BCE, the range of elephants no longer extended across China but had retreated southward to the Huai River basin.^[5]^{: 87-88、73}

Spring and Autumn period

Under the early feudal system, fiefs occupied certain territories, while remaining land belonged to no one.^[7]^: 173 Mountains, forests, rivers, and marshes were originally open public spaces.^[11]^: 51 By the Eastern Zhou, as state control expanded, governments appointed officials to tax resource exploitation in remote areas.^[7]^: 173 To enrich the state and strengthen the military, rulers monopolized mountains, forests, rivers, and marshes and imposed tariffs.^[11]^: 51 During the Spring and Autumn period, land belonged to the ruler; under feudalism, famous mountains and great marshes within feudal states belonged to the Son of Heaven. Utilization of mountain, forest, river, and marsh resources was limited by time but not by users. Benefits from these resources were shared between rulers and the people, but use had to occur within specified times.^[12]^: 16–17 Feudal states attached great importance to forest protection, with strict forestry laws. Because population was sparse and land abundant, the incentive for people to destroy forests was not strong.^[4]^: 20 After the mid-Spring and Autumn period, rulers turned mountains, forests, and marshes into private property and taxed those who used their resources.^[13]^: 487 This was equivalent to indirect prohibition through taxation. Forestry laws prevented reckless felling, and mountain and forest access for harvesting was seasonal. Entering mountains to harvest beyond the permitted period or felling trees that should not be cut was called "stealing wood" and subject to punishment. Some forests were completely closed, with even harsher penalties for violations.^[4]^: 20–21 The southern state of Chu had more forests than the central states. By the 6th century BCE, forests had become very scarce in the coastal area of northeastern Shandong.^[2]^{: 56、51-52} Around 500 BCE, iron tools began to appear and were soon used in agriculture and for making iron plows. The first to use iron farming tools were the state of Wu.^[5]^: 89、91

Warring States period

By the 4th century BCE, iron-smelting technology had spread widely in the Yangtze River basin, and northern feudal states began mass-producing iron tools. Iron foundries required large amounts of wood to make charcoal for smelting ore; wood was scarcer than ore, so large-scale deforestation and environmental destruction became common.^[5]^{: 91-92、89} In densely populated areas, all woodland around cities had disappeared, and farmland of the various feudal states adjoined one another. Due to excessive timber cutting, areas near the capitals of large states became bare Ox Mountain.^[4]^: 7 By around 300 BCE, people had thoroughly altered the land of North China. Mencius criticized the felling of Ox Mountain's forests. To increase revenue, rulers of the various states opened wastelands and forests for farmland to recruit farmers, attract migrants, and expand the agricultural population.^[5]^: 8、90 During the Warring States period, digging irrigation canals was common practice. For example, the state of Qin built the Zhengguo Canal, diverting water from the Jing River into the Luo River over 126 km to irrigate and flush salts from saline-alkali land between the Jing and Luo, turning wasteland into fertile fields.^[7]^{: 234–235} This completed agricultural reclamation in the Guanzhong region. The Warring States competed to control forests, wetlands, and minerals, appointing officials to manage and tax them to strengthen state power.^[7]^{: 242、288} The Shang Yang reforms [zh] made the benefits of mountains, forests, rivers, and marshes the exclusive property of the ruler and established officials to collect taxes on them.^[12]^: 18 The state took control of forests and marshes that had once been communal resources, thereby exercising far greater control over the natural ecology within its territory than ever before.^[7]^: 301

In the eastern part of the Guanzhong Basin, soil erosion began to intensify due to agricultural expansion. In the densely populated areas of the North China Plain, pastures within farming regions became increasingly scarce; the growing population encroached upon the living space of herbivorous livestock such as cattle and sheep, leaving only animals like dogs, pigs, and chickens—which could survive in human settlements—behind .^[7]^{: 105、193} The Zhou people developed wetlands along riverbanks and in poorly drained areas, causing the deer and water deer—two species that inhabited these wetlands—to eventually disappear from the Yellow River basin. As farmland expanded, deer herds in the lowlands dwindled, and most of the remaining land was used for grazing cattle, sheep, and goats.^[7]^{: 113–114} By the end of the Warring States period, large wild animals in the North China Plain were few and far between, and aurochs, wild horses, and wild water buffalo eventually became extinct. From then on, large animals in the North China Plain were found only in the royal game reserves [zh]^[7]^{: 119、242}. The three northern states of Qin, Zhao, and Yan expanded northward, occupying semi-arid farming and pastoral zones, then advancing further into nomadic territories.^[7]^: 204 They drove nomadic peoples from their pastures and built the Great Wall to defend against their attacks. The Central Plains states needed resources from the grasslands, especially horses for cavalry and pasture for grazing. Facing incursions from the Central Plains, the Xiongnu formed alliances to resist.^[5]^: 96–98

During the Warring States period, people gradually realized that nature's bounty was not limitless and needed timely maintenance to prevent resource depletion and food shortages. Mencius emphasized land management, advocating soil and water conservation measures and urging the royal family and wealthy to live moderately to avoid exhausting resources. The Guanzi, compiled around 250 BCE, pointed out that natural resources were finite and that successful rulers should strictly limit resource exploitation to prevent exhaustion. However, due to the pressures of war, resource protection policies rarely succeeded in the various states.^[5]^{: 127、125、93}

Qin and Han dynasties

Central Plains

The agricultural empire model created by the Qin and Han became the way most Chinese dynasties organized the state for the next two thousand years. The Qin government undertook massive projects. To supply timber for building palaces in Xianyang and the Great Wall, forests in the Inner Mongolian Plateau and nearby mountains were destroyed.^[5]^: 74、100 The Qin also developed forests in the south.^[2]^: 58 Convict laborers were used to fell forests in the upper reaches of the Han River basin.^[7]^: 292 The Qin-Han government built roads connecting the entire empire, promoting agricultural development in the south, southwest, and northwest. More and more land was altered by humans. During the Han, agricultural production increased on the North China Plain and the population grew significantly. By 2 CE, the national population reached 60 million, and natural ecosystems were replaced by agricultural ones.^[5]^{: 107、110、112} Han people knew how to plow with iron plows and fertilize with manure, eliminating the need for fallowing to restore fertility. The extensive slash-and-burn system of rough cultivation almost completely disappeared.^[4]^: 9 The expansion of farmland destroyed large areas of forest on the North China Plain. By the mid-Han, forests on the North China Plain had been largely felled, with only the Taihang and Qinling Mountains retaining forest cover. The once-forested hills of the Shandong Peninsula were planted with economic trees such as fruit trees.^[5]^{: 99、111-112} The previously diverse human settlements and natural environments of northern China had now become homogenized. Iron foundries continued to destroy forests. In the Western Han, there was a case where an iron foundry, having exhausted the trees on nearby hillsides, caused a hillside collapse that buried over a hundred people.^[5]^: 132、92

The state of Qin monopolized mountain and forest management. After unifying the six states, it ordered the entire empire to "not fell grass or trees."^[4]^: 22 It enacted laws restricting reckless exploitation of natural resources to protect the empire's resources for regeneration.^[11]^: 56 The Qin had officials responsible for managing forests and marshes. They were to respond to fires, illegal logging, and over-hunting of wild animals. The state gradually took control of mountainous areas and regulated and taxed tree planting and forestry.^[7]^{: 290、308-309} Laws declared mountains and marshes state property and did not allow long-term private occupation. Agriculture did not need to expand into mountainous areas.^[4]^: 16 Ordinary farmers could not freely enter mountains, marshes, or forests. The Qin and Han governments also enacted laws prohibiting woodcutting in specified months. Rulers also designated imperial hunting parks closed to felling and entry year-round, the largest of which was the Shanglin Park [zh] south of Chang'an.^[13]^{: 501、494} After the Han salt and iron monopolies [zh], prohibitions on mountains and marshes became stricter, but periodic openings for public harvesting were still allowed. In special circumstances, the government would temporarily lift restrictions for short periods.^[4]^: 22 The First Emperor of Qin had a vast imperial hunting park beside Xianyang, and Emperor Wu of Han built an even larger Shanglin Park connected to Chang'an. These parks resembled nature reserves, containing mountains and water, wild animals, rare plants, and palaces. People realized that unrestrained harvesting brought adverse consequences for wild food sources. The Qin and Han governments also implemented environmental protection measures, enacting laws called "Monthly Ordinances" that prohibited drying up ponds or burning mountain forests. However, people did not strictly observe them, believing that agricultural development was far more important than environmental protection.^[5]^{: 118、127}

Northwest

To attack the Xiongnu, Emperor Wu of Han mobilized over 12.5 million people, destroying the Xiongnu and five Central Asian kingdoms. Han soldiers advanced into the Central Asian interior and the edge of the Gobi Desert. The Central Plains originally had little pasture suitable for raising animals. To build a cavalry, Emperor Wu established 36 pastures on the western and northern frontiers, dispatching about 30,000 slaves to tend horses. To completely solve the Xiongnu problem, Emperor Wu wanted to turn the occupied Xiongnu lands from grassland into farmland, cultivated and settled by Han people. Up to a million Han people were relocated from the North China Plain to the Hexi Corridor and from there expanded into the Tarim Basin. The colonization and grassland transformation plan was quite meticulous.^[5]^{: 101、103} First, military watchtowers were built, followed by garrison towns near water sources and arable land. Military and civilian personnel turned the area into farmland, then built houses equipped with furniture and farm tools, settled the relocated Han people, and began cultivation. As colonization and military farming progressed, military rule gave way to civil administration, and the entire region was incorporated into Han territory. Emperor Wu stationed troops in the Hexi region while also relocating civilians to strengthen the border, establishing the Four Commanderies of Hexi and 35 counties, greatly increasing the local population.^[4]^: 11

Emperor Wu's management of Hexi and the tuntian policy accelerated the deterioration of Hexi's geographical and ecological environment.^[4]^: 11 In the early Han, animal husbandry flourished in the Gansu Corridor, with vast grasslands and small deserts.^[14]^: 389 Most of the Hexi Corridor was originally grassland oasis with abundant water and grass, and the Qilian Mountains had extensive forests. The tuntian areas were located on the edge of the desert, where forests were already sparse. Tuntian activities did not expand windbreak forests but instead first cut down trees. Sometimes excessive water use in upstream tuntian areas affected downstream water supply, causing rivers to change course. Original oases became desolate and disappeared, eventually turning into desert. Examples include Luotuo in Gaotai County and Suoyang City in Anxi, both harmed by artificial river course changes, with land gradually desertifying. The wild grass vegetation on the desert edge originally served as a natural barrier against wind and sand. Crops, however, left large gaps between plants, making it difficult to block wind and sand. Moreover, crops were harvested in autumn, leaving the ground completely bare for about half the year, precisely when wind and sand were strongest. Tuntian farmland had no vegetation to block wind and sand, leading to desert encroachment. Even more unfortunately, when the Han dynasty's national strength weakened and the policy of relocating civilians to strengthen the border was halted, people withdrew from the tuntian areas. The former tuntian zones became large areas of abandoned land with long-term bare ground. Without even the weak wind and sand blocking effect of crops, strong winds carried large amounts of sand particles deep inland, causing the desert to expand year by year.^[4]^: 41、12 Plowed grasslands began to suffer wind erosion and desertification, bringing lasting environmental damage and species extinction. When farmland lost Han maintenance and water sources, former grassland areas turned into desert rather than naturally reverting to grassland. In the Tarim Basin, the Han developed oases rather than grasslands, a method that was more sustainable in the long term.^[5]^{: 104–105}

River management

Upper reaches of the Yellow River in Qinghai Province

During the Western Han, to develop agriculture, grasslands along the middle reaches of the Yellow River were cleared; to meet the capital's demand for timber, temperate forests in the upper reaches of the Yellow River were felled, resulting in soil erosion.^[2]^: 27 Land around the Yellow River basin had already been cleared for agriculture and smelting. Large amounts of yellow sediment entered the river. The Yellow River water was said to contain about 60% sediment.^[5]^: 115 The river turned yellow and began to be called the "Yellow" River.^[2]^: 27 In winter, when river flow slowed, sediment accumulated in the riverbed, raising it every year at an average rate of about 0.91 metres (3 ft) per century, increasing the risk of flooding.^[5]^: 116 Between 186 BCE and 153 CE, Yellow River dikes breached approximately every 16 years.^[2]^: 28 Major breaches occurred in 168 BCE, 131 BCE, 39 BCE, and 29 BCE. In 11 CE, a historic breach occurred, causing the Yellow River to change course.^[5]^{: 116–117}

South

During the Han, people rarely developed the south because the hot, humid climate was unsuitable for the grains (millet, barley, wheat) grown by northern Han people, and the many deadly diseases native to the south also deterred northerners. At that time, the Han had not yet learned how to transform the south's wet environment into high-yield rice paddies.^[5]^: 132 In the lowlands of Lingnan, the Zhuang people cultivated rice, farming the same land year after year, while the Yao living in hilly areas practiced shifting slash-and-burn cultivation. The Li on the coast and Hainan Island practiced even more casual grain cultivation.^[15]^: 55–56

Wei, Jin, Northern and Southern dynasties

North

The disaster of Yongjia in 311 caused a massive population decline in the north, with large numbers of Han people migrating south to the Yangtze River basin to escape chaos. Northern China experienced wave after wave of nomadic invasions, while many Han people retreated to mountain forts (wubao).^[5]^{: 136–137} During the 4th–5th centuries, there were hundreds of forts in northern China. With sparse population and large areas of abandoned land, both Han and non-Han rulers tried to resettle farmers on the fields. Invaders tried to capture Han farmers and confine them to secure zones they controlled, concentrating them near the conquerors' capitals. After people were taken away, the occupied land was abandoned.^[5]^{: 138–139} Mark Elvin noted that due to the southward movement of pastoralists, grasslands and forests in North China regenerated, and Yellow River breaches decreased to once every 50 years or less.^[2]^: 28 Robert Marks, however, argues that northern forests did not regenerate or recover because most had already been felled during the Han, leaving almost no seed sources. Troops constantly marched through the land, making it difficult even for shrubs to grow. Nomadic peoples brought grazing animals, turning former Han farmland into pastures for millions of horses and sheep. Sheep grazed plants bare, inhibiting the regeneration of trees and shrubs. The range of tigers shrank dramatically as their habitats and food sources were destroyed, leading them to begin attacking humans and eating people.^[5]^{: 140、192}

South

During the chaos of the Yongjia Disaster, hundreds of thousands to a million Han people fled south to the Yangtze River basin and even further to the South China Sea (Guangzhou).^[5]^: 142 Han people drove out southern natives and settled there. Southern land was densely covered with rivers and lakes, with dense forests covering hills and mountains, originally unsuitable for agriculture. The Yangtze Delta and Hangzhou Bay areas were still uninhabitable. (During the Warring States, the state of Yue settled on higher hills, slopes, or alluvial fans rather than in swamps and low river valleys.) The lowlands were filled with brackish water, with fluctuating water areas and levels. People on higher plains could farm, while those in low plains and coastal sandy areas engaged in salt production and fishing. At that time, aristocratic families from the lower Yangtze began investing large amounts of labor and resources to gradually transform southern land into rice paddies, replacing forests and swamps with farmland.^[5]^{: 145–147} To ensure rice growth, the Han needed to level the land thoroughly before cultivation, build dikes around fields, and install sluice gates for drainage and irrigation. The Han were able to drain and tame low-lying land. The entire Yangtze River basin's river valleys were transformed, and beyond rice paddies, flood-control dikes were built, massively altering the south's wet environment.^[5]^{: 147–149} In the lower Yangtze, new settlements were located on lower plains and river valleys suitable for rice cultivation, with dense mountain forests between fields inhabited by non-Han "Man," "Lao," "Li," and "Xi" peoples whose lifestyles had not yet been assimilated by the Han.^[5]^: 144

During the Eastern Jin, powerful families seized mountains, lakes, rivers, and marshes.^[12]^: 21 Great clans illegally occupied mountains and marshes. In 336, the Eastern Jin issued a strict prohibition against occupying mountains and marshes, known as the "Renchen Regulation." However, it was difficult to enforce effectively, resulting in powerful families violating the law by occupying mountains and sealing waters, while the government was powerless to punish them. Common people had no such privileges, creating extreme unfairness.^[4]^: 23 Because it was difficult to strictly prohibit powerful families from occupying mountains and sealing waters, during the reign of Emperor Xiaowu of Liu Song (453–464), the regulation was changed. While reaffirming that occupying mountains and marshes was an encroachment on state-owned land, it recognized existing private property as a fait accompli.^[12]^: 21–22 This allowed private individuals to legally own mountains and marshes, but with limits based on official rank. From then on, mountain and forest property rights in the Southern Dynasties operated under a dual-track system of state and private ownership. Private individuals could legally acquire mountain and forest property rights. Open access to mountains and forests became the norm, with strict closures being special cases. With private ownership of mountains and forests permitted, in suitable areas people transformed occupied mountain land into terraces for water storage and rice planting; in unsuitable mountainous areas, they turned them into millet fields, continuing the early slash-and-burn fallow system.^[4]^: 23、9

West

In the 4th century, Lao tribes appeared in northern Sichuan. They lived in lowlands along rivers and practiced shifting cultivation, burning part of the forest and planting taro and millet in the ashes until the soil's nutrients were exhausted after a few years, then moving to the next forest patch. The Lao were forced by the Han to leave the lowlands; some retreated to the mountains, while most chose to adapt to Han life. In the highlands of Sichuan, the Yi lived in fortified villages on mountain tops. To provide pasture for their livestock, they burned forests in the mountains. Later, as the Yi population grew and they moved into lowland forests, they still practiced slash-and-burn agriculture. When competing with the Han for land, the Yi would retreat to their mountain-top fortresses.^[5]^{: 187–188}

Sui and Tang dynasties

North

During the Tang, forests in the north had been largely felled.^[5]^: 184 During the Sui and Tang, the Zhongnan Mountains could generally only supply the capital's daily firewood needs. Even so, after the mid-Tang, even firewood began to fall short, and larger construction timber had to be obtained from prefectures such as Lan and Sheng [zh].^[4]^: 35 To protect Chang'an from soil erosion from surrounding hills and to raise awareness of natural environmental protection, the Tang issued laws. Perhaps influenced by Buddhist precepts against killing, the Tang also enacted laws restricting killing and hunting seasons. People recognized the serious consequences of forest degradation but could do little to save China's forests. To supply fuel, large numbers of trees planted along Chang'an's main roads were felled.^[5]^{: 180-181、210} During the mid-Tang, all accessible pine trees in present-day Shandong, Shanxi (Taihang Mountains), and Shaanxi had been felled, mainly to burn pine smoke for ink production.^[8]^: 79 As the riverbed continued to rise, dikes were built along both banks of the Yellow River during the Tang, and the soil for raising the dikes was dug from nearby areas, increasing the height difference between nearby land and the river. Seepage turned many low-lying areas into swamps, and because salts in the water could not drain away, a belt about 3.2 kilometres (2 mi) wide along the river became uncultivable saline-alkali land.^[5]^: 195

During the Tang, the Hexi Corridor became a major transportation route and part of the Silk Road. As population increased, suitable land was colonized and turned into farmland, resulting in desert expansion and shrinkage of the Dunhuang oasis. The desertification process was irreversible.^[14]^: 389 During the Tang, Buddhist monasteries also altered the natural environment. Monasteries were generally built in uncultivated mountainous or hilly areas or other unused land. During the Sui, there were over 4,000 large monasteries distributed across north and south China, each overseeing large numbers of farmers and servants who cultivated land for them. Monasteries were also surrounded by trees, gardens, and pastures. They cleared mountainous land for farmland, pastures, orchards, and timber forests, transforming original forests into various productive arbor or shrub forests, such as tea gardens and orchards (orange trees were most common), and planted construction materials such as timber and bamboo.^[5]^{: 177–178}

Jiangnan

In the Yangtze Delta region, Han rice cultivation was mostly limited to higher elevations. By the 9th century, the Han had invented new water control techniques and began effectively reclaiming low-lying areas.^[5]^: 158 At that time, the main problem facing farmers was flooding. Annual monsoon rains caused major floods in the Yangtze, overflowing riverbanks across the middle and lower reaches into plains, lakes, and marshlands. The Han solved this with polder fields (weitian)—completely enclosing farmland with earthen dikes to prevent floodwater entry. Sluice gates in the dikes allowed drainage and irrigation. The level of farmland inside the dikes was lower than the surrounding floodwater or river water, enabling farmers to have ample irrigation water while preventing floods. However, building polder fields exceeded the capacity of individual households and was often completed by wealthy landlords. Tang farmers also popularized the method of raising fish in rice paddies, allowing fish to eat weeds and mosquito larvae while fish manure increased field fertility.^[5]^{: 169、174}

During the Tang (and subsequent Song, Yuan, Ming, and Qing), people practiced slash-and-burn cultivation on mountainous land, called "she tian." Before sowing, trees had to be felled, along with shrubs and tall grass. She tian did not use plows or turn the soil and was an extensive cultivation method. After felling trees, people waited for rain before burning the grass and wood on the ground. After the rain, while the ashes were still warm, they sowed seeds without irrigation. The crops planted were dryland ones such as millet or glutinous millet. This extensive cultivation method could not maintain soil fertility and required shifting fallow. Some moved annually, others after two or three years of planting. After leaving, the original land needed seven or eight years to regrow trees and wild grass before slash-and-burn could be repeated. In mountainous areas where she tian prevailed, there was a special group called "she tian fu" who owned no land themselves but specialized in traveling to perform slash-and-burn work for others. They would agree in advance on work for a certain family's she tian. Although she tian fu might travel hundreds of li to arrive on schedule, they brought their own tools.^[4]^: 9–10

Lingnan and southeastern coast

Both the Sui and Tang dynasties sent armies south to Lingnan and colonized the area, clashing with the indigenous peoples. In the waterlogged swamps, the air was very humid, and parasites and mosquitoes proliferated in large numbers.^[5]^{: 158、163} Standing water on the ground and swamps left after river floods allowed Anopheles mosquitoes and malaria to thrive in Lingnan.^[15]^: 70 To northern Han people, the entire Lingnan region was plagued by epidemics, with miasma (malaria) prevalent. Tropical forests were breeding grounds for various parasites. Lingnan's miasma kept the Han out of the low river valleys.^[5]^{: 162、159} At that time, most Han settled in northern Guangdong and Guangxi, where there was no miasma threat, while the Dai indigenous people living in the lower river regions had some degree of immunity to malaria.^[15]^: 71、73 In multiple Han military campaigns against indigenous peoples, one-quarter of the troops were lost to malaria. Huang Chao's forces also suffered 30–40% mortality from malaria before withdrawing from Lingnan and moving north. The Han were helpless against miasma, and western Lingnan and further west in Yunnan remained under indigenous control. More thorough environmental change in southern China would have to wait until the Han population became larger and denser.^[5]^{: 162、160}

During the Tang, most of Lingnan was still covered by forest, but the original deciduous broadleaf forests on the highlands had been burned and replaced by secondary coniferous and fir forests.^[5]^: 160 At that time, the lower reaches of the West, North, and East Rivers were all densely marshy and difficult to cultivate.^[15]^: 73 Indigenous Tai-speaking groups cultivated rice in the lowlands, farming the same land year after year, while the Li, Miao, and Yao in higher mountainous areas practiced shifting slash-and-burn cultivation.^[5]^{: 157、159} They used slash-and-burn methods, constantly migrating, combining agriculture with hunting and gathering.^[15]^: 67 The Moyao people hunted in highland forests after the autumn harvest, burning wild grass to promote new growth and attract deer herds for hunting.^[5]^: 157 The Han did the same with slash-and-burn. In the dry winter months, they burned forests on mountain slopes, then many families together sowed seeds in the ashes, harvesting for a few years before moving to another plot and establishing a new settlement, allowing the original exhausted plot to regrow vegetation.^[15]^: 67 In higher mountainous areas, especially along the watershed between the Yangtze and West Rivers, forests were often cleared to plant tea. Unlike annual crops, tea bushes provided a certain degree of soil protection.^[8]^: 80 Highland residents also used girdling, topping, and felling to clear mountain forests, opening clearings in dense tree canopies to allow sunlight to reach the ground for planting tuber crops such as taro.^[5]^: 158 Slash-and-burn cultivation in the upper reaches of rivers caused erosion in mountainous areas, sending more sediment into the lower reaches of the Xi, Bei, and Dong Rivers, depositing it in the floodplains of the Xi, Bei, and Dong Rivers and becoming fertile soil, while also bringing problems of flooding and malaria.^[15]^: 68

In the Fujian region, the indigenous Yue people spoke Austronesian languages and primarily lived by fishing and hunting, possibly also practicing slash-and-burn rice cultivation. Many places in southern Fujian were saltwater marshes and habitats for saltwater crocodiles. Inland mountains blocked Han entry into the region, so Han arrival on the southeastern coast came much later than in Lingnan. By the 8th century, Han immigration to Fujian began to increase. Locals built river dams and developed rice paddies. The Han not only battled the environment and saltwater crocodiles but also used military force to drive the Yue from the valleys. The Tang established tuntian to control the area. Many indigenous people fled to the mountains, while the remainder accepted Han assimilation. Both the Yue and saltwater crocodiles disappeared, replaced by the Han and their farmland.^[5]^: 161

Song dynasty

North

From the Song onward, ecological conditions in the south and north changed relatively. The northern ecosystem gradually deteriorated, with massive forest reduction. The ground lost its temperature-regulating function, average annual temperatures dropped, and the frost-free period [zh] shortened, reducing the growing season for crops. At the same time, rainfall also decreased, turning the north into a semi-arid region. After severe destruction of natural vegetation, soil erosion intensified. Combined with the loose soil of the Loess Plateau, which was easily eroded, most rivers in the north had increased sediment loads, causing siltation and flooding, especially the Yellow River, which gradually became an "elevated river." Its lower reaches frequently changed course. Lakes on the northern plains were successively filled in, eliminating their natural flood storage and detention functions and causing frequent floods. During the same period, the south was still able to maintain ecological balance. Due to higher temperatures and rainfall, the self-regenerating capacity of natural vegetation was stronger. The entire ecosystem was not as fragile as in the north, and the deterioration process was relatively slow.^[4]^: 14–15

China's population exceeded 10 million households during the Han and Tang peaks but reached 20 million households (1–1.2 billion people) during the Song. By 1000 CE, almost the entire North China Plain had become farmland. By the mid-1070s, the Taihang Mountains had lost their pine forests and become barren.^[5]^{: 172、217、199} Timber shortages during the Song affected the iron and steel industry. Iron smelting originally relied on charcoal as fuel, but the Song's booming iron industry faced shortages of firewood and charcoal and substituted coal. Coal also began replacing firewood in northern households for heating and cooking. To block Liao cavalry, the Song dug many ponds and marshes along the northern border. To fill these ponds and marshes with water, artisans diverted seawater and altered river courses and built dikes. The Song also had local soldiers and civilians plant rice for self-sufficiency, but due to the overly cold climate, this tuntian plan failed. The ponds and marshes became breeding grounds for mosquitoes and black flies.^[5]^{: 185、171} In the Liao state, the grasslands in what is now eastern Inner Mongolia's Horqin region began to desertify. Local Khitans learned farming but used very extensive methods. Newly reclaimed land lost fertility after three to five years, so people sought new reclamation areas. Original farmland was abandoned, the surface exposed without vegetation protection, beginning the process of wind erosion. During the Jin, the area reverted to pasture, with some secondary grasslands and forests appearing, restoring some of the former landscape.^[4]^: 47–48

River management

In the section where the Yellow River flows north toward the Bohai Gulf, the Song worked hard on river management, reducing main channel pressure through diversion channels and strengthening dike maintenance. Sometimes they built breakwaters deep in the river channel to reduce water flow impact, and sometimes they laid large amounts of vegetation to protect the dikes.^[5]^: 196 The Northern Song government also diverted the Yellow River northward from the border area between present-day Hebei and Henan, forming a channel on the North China Plain, hoping to use this flooded terrain and artificial ponds to block Liao invasions, but without success. The Yellow River continued changing course on the North China Plain for 80 years, with floods frequently inundating fields, spreading disease, and causing great suffering. Most of the sediment was nutrient-poor sand that only turned farmland into wasteland.^[16]^{: 232、234} Many small rivers on the North China Plain were blocked by sediment deposition and collectively changed course or dried up. To repair river dikes, local residents felled all trees and shrubs in nearby hills for dike support. Because the North China Plain was very flat, floodwater could not drain, causing waterlogging and salinization of the land. Large areas lost their original vegetation. Wind carried sand and dust across the plain, forming dunes. Lakes and ponds silted up, and the silt quickly became very infertile. Much originally fertile land turned into sandy ground.^[5]^{: 198–199} In 1128, in winter, the Bianjing defender breached the Yellow River dike about 80 kilometres (50 mi) north of Kaifeng to relieve the siege of the capital. By 1194, floods and silt finally caused the Yellow River to change course southward, occupying the Qing River and Huai River channels and entering the sea south of the Shandong Peninsula, forming a new large lake, Hongze Lake, at the river mouth. This sea area also became the "Yellow Sea" due to Yellow River inflow.^[5]^{: 196、199} After the 1194 Yellow River course change, the abandoned northern channel became a source of sediment. When winds rose, sandstorms ravaged the entire North China region. On the river channel, "the wilderness had no grass and the five grains did not grow."^[5]^{: 196、199}

Before the Northern Song, siltation of lakes on the North China Plain was slow. After the Southern Song, conditions worsened. The sediment load carried by the Yellow River increased, and flooding frequency rose. Many lakes in the Yellow River basin were filled in after several Yellow River floods. The largest lake in ancient North China was Daluze [zh], located near Julu County. In 1108, the Yellow River changed course northward, flooding Julu City. Daluze also silted up, with its lakebed rising and surface shrinking. Juyeze in Shandong, whose surface was said to span 800 li during the Northern Song (the Liangshan Marsh in Water Margin), received Yellow River water in 1019 and 1077 when the river breached twice. During the Jin, when the Yellow River changed course southward, Juyeze lost its water source. Water receded and sand remained, creating large areas of shoals that were reclaimed by nearby residents. In 1180, the Jin government even sent envoys to recruit refugees for tuntian in Liangshan Marsh. Smaller lakes silted up into flatland even earlier. For example, Heze, Leixiaze in Shandong, and Mengzhuze in Henan had already become flatland during the Song.^[4]^: 91–92 During the Southern Song, officials responsible for irrigation and canal systems began worrying about upstream deforestation and noted the impact of salinization and flooding on downstream areas.^[17]^: 19

Jiangnan

During the Tang and Song dynasties, people expanded the vast low-lying and marshy plains of the Yangtze Delta through drainage methods, with the Song dynasty being particularly enthusiastic about the effort.^[18]^{: 272–273}. In the low-lying areas of the Yangtze Delta, the government organized substantial human and material resources to construct many large polders (fields created by building dikes to enclose lakes for cultivation), thereby increasing the area of farmland and raising tax revenue. From the late 11th century to the early 12th century, more than 2,000,000 hectares (5,000,000 acres) of land in the Yangtze Delta region were opened through polder development.^[5]^: 169. In the Northern Song period, most polders around Tai Lake were organized by stationed troops with strict management; ordinary residents were prohibited from imitating the practice, and the prohibitions were quite rigorous. Around 1112, these restrictions began to be relaxed, and privately managed polders started to appear along the shores of Tai Lake.^[4]^: 100. A dense network of waterways connected the individual rice paddies, providing both sources of irrigation water and a transportation network. The establishment of polders, together with the introduction of early-ripening, drought-resistant rice varieties, greatly increased total grain output. Farmers discovered that draining the rice paddies once a year improved the soil's performance, fertility, and productivity. In low-lying farmland areas, people divided the polders into smaller plots that were easier to manage, while establishing cross-village cooperative irrigation management mechanisms. This allowed even low-lying or swamp-like fields to be drained once a year. The area under double-cropping expanded continuously, and more and more forests and marshes were converted into farmland.^[5]^{: 171–172}. During the Northern Song, the Tai Lake region in the lower reaches of the Yangtze had fertile land, rare floods, and ecological balance. During the Southern Song, the local population increased significantly, and people enclosed lakes to create fields, causing floods to become more frequent. The Southern Song government initially encouraged the people to widely open polders in the Tai Lake area, which affected the lake's water storage capacity. During flood periods, the water had nowhere to drain, resulting in disasters. The Southern Song government then changed its policy, restored the ban on "stealing" lakes (encroaching on lakes), and even forcibly abolished fields to restore lakes.^[4]^{: 15, 100–101}.

Early-ripening rice revolutionized Song dynasty agriculture. By the 13th century, many hilly areas in the lower Yangtze region and Fujian—where water supply or soil conditions had previously been unsuitable for rice cultivation—were transformed into terraced fields. The landscape of the eastern half of China's rice-growing regions underwent a thorough transformation.^[5]^: 172. Terraced fields became widespread in the Southern Song. On relatively low mountain ridges, terraces were built layer upon layer, extending all the way to the mountain tops. Although the terraces replaced forests on the mountains, they did not cause soil erosion on the slopes. Instead, they retained runoff from the slopes layer by layer, preventing the soil from being washed away and preserving the ecosystem. In contrast, slash-and-burn fields (she tian) in mountainous areas had the opposite effect. These fields did not alter the slope of the mountain land, so the erosive force of rainwater remained strong. After the natural vegetation was burned away, the ground was either left bare or sparsely planted with dryland crops, making it impossible to conserve soil and water and causing severe ecological damage.^[4]^: 16–17. Many forests in the Yangtze River basin no longer existed, surviving only in some hilly and mountainous areas south of the Yangtze. Tigers could still find habitat there, but elephants, which preferred to live in low-lying places, had disappeared from the Yangtze basin.^[5]^: 192.

From the Southern Song onward, fish ponds were commonly dug in southern mountain valleys, alluvial plains, or delta plains. Fish fry were raised using residues, garbage, and silkworm feces, producing more food per unit area.^[8]^: 82. In the mountains south of the Yangtze, the Miao people and Yao people planted Chinese fir trees for trade and profit.^[17]^: 101. On the other hand, ocean currents carried large amounts of sediment from the new mouth of the Yellow River to the Hangzhou Bay, approximately 320 kilometres (200 mi) away, where it was deposited. This increased the land area along the coast of Jiangsu and boosted rice production there.^[5]^{: 197–198}.

Central China and Sichuan

Before the Northern Song, Dongting Lake in the Jianghan Plain was still expanding, with abundant water volume. During the Northern Song, Dongting Lake reached its maximum width and depth. From the Southern Song onward, as northerners migrated south and grain needs increased, people began enclosing fields for farmland, competing for fertile lake fields. From then on, the lake surface gradually shrank, water capacity declined, and floods caused disasters when they arrived, breaching dikes and inundating fields and houses.^[4]^: 93–94 At the same time, population growth in the lower Xiang River led many farmers to practice slash-and-burn in mountainous areas, destroying forests and turning local mountains into bare hills. Fortunately, the Xiang River region's forests had strong regenerative capacity. In many areas, after forests were destroyed, secondary forests could grow after several years. Moreover, due to inconvenient transportation in some areas and excessively high mountains that reclamation teams could not reach, some original forests were still preserved.^[4]^: 15 The Song emphasized colonization of Sichuan. After indigenous peoples were assimilated or driven into the forests, Han farmers settled in the river valleys and cleared land. By the 11th century, forests in many areas had been largely felled.^[5]^{: 187、159} Many areas in the region were transformed. Farmers dug hillsides into terraces, stored rainwater, and then planted early-maturing rice varieties. Large areas of forest in Sichuan were felled. The "forbidden mountains" that had once separated Han and indigenous territories were almost completely deforested.^[5]^{: 189–190}

South China

During the Song, the population of Lingnan continued to increase, but due to fear of malaria, they remained in northern Lingnan and dared not move to other parts of Lingnan. At that time, malaria was mostly found in the alluvial plains of southern rivers rather than upstream areas. From the 11th century, the growth of the Pearl River Delta accelerated.^[5]^{: 164-165、200} Flood control projects on the Pearl River carried more sediment from upstream to the Pearl River estuary, blocking the view of the sea looking south from Guangzhou. Slash-and-burn agriculture in the upper reaches of the Pearl River system caused soil erosion, sending more sediment down the Dong, Xi, and Bei Rivers. The floodplains in the lower reaches of these rivers, especially where the Dong and Bei Rivers converged, had very fertile soil. These lower river reaches generally flooded every year. As early as 809, the Tang built embankments to prevent the southward-flowing Xi River from joining the northward-flowing Bei River, allowing floodwater to continue flowing downstream. Around 1100, construction began on the Sangyuanwei project, eventually building a dike about 45 kilometres (28 mi) long that protected about 40,000 hectares (100,000 acres) of land from flooding.^[5]^{: 201–203} This created a new era of agricultural development in the Lingnan region. At the same time, seawalls were built in Leizhou Prefecture and western Dongguan,^[15]^: 74 creating nearly 45 kilometres (28 mi) of coastal defense dikes that blocked periodic tides and typhoons, adding 65,000 hectares (160,000 acres) of arable land. However, coastal mangrove forests also disappeared as a result.^[5]^: 203

In the Song dynasty, a total of 28 dike enclosures were constructed along the upper reaches of the Pearl River, with a combined length of 66,024 zhang, protecting 24,322 qing of farmland. The flood-control dikes confined the rivers to fixed channels so that, during the rainy season, the water would not overflow or burst into multiple channels. Instead, the river water flowed directly into the bay area, turning the former floodplains into land suitable for agriculture. By draining the swamps and waterlogged areas created by flooding, the ecological environment of the malaria vector Anopheles mosquito was altered, making these regions less dangerous to Han Chinese settlers.^[15]: 75–76 In the mountainous areas north of Guilin, densely growing cinnamon trees produced cassia bark (cinnamon spice). By around the year 1000, most of the original forests around Guilin had been felled.^[5]: 160

Land ownership

During the Song, mountain and forest property rights underwent nationwide changes, with private ownership of mountains and forests fully recognized. Previously, mountains and forests belonged to the state. People could use mountain and forest resources but could not occupy or reclaim them. During the Song, almost all plain land had already been reclaimed. The government allowed people to legally occupy mountains and marshes, so people began large-scale competition with mountains for land and with water for land. Many mountainous slopes were transformed into terraces, while others became she tian with slash-and-burn cultivation. In some mountainous areas limited by conditions and unable to be reclaimed as fields, they were turned into private forest farms for growing trees. In other mountainous areas that were too steep and inaccessible, mountain owners simply left them idle, retaining only ownership rights but finding it difficult to utilize them. Some mountainous areas remained state-owned forests, but the scope of such forest areas gradually shrank. The government's basic attitude was to open mountains and forests as much as possible, only choosing to close certain forest areas. There was essentially no management of state-owned forests, which were open to anyone for felling, with only slight tax collection called "choufen."^[4]^: 24–25 During the Northern Song, enclosing lakes for farmland around Tai Lake in the Jiangnan region was prohibited and called "stealing lakes." By the early Southern Song, as large numbers of northern residents migrated south, to supply food, the government officially recognized enclosing lakes for farmland as legal and even used government power to promote it. As a result, lake enclosure for farmland quickly spread throughout Jiangnan. Countless small lakes were soon enclosed and filled, while larger lakes also rapidly shrank.^[4]^: 99

Yuan dynasty

North

The Mongols massacred people and attempted to turn all of northern China into their pastureland. Wherever Mongol armies went, city walls and agricultural facilities were razed to the ground. Dams no longer existed, irrigation canals were cut, leaving behind swamps. Grain seeds were burned, fruit trees were sawed down, shelterbelts were felled to the ground, and farmland became desolate, dry grassland exposed to wind and sand. It was not until the reign of Kublai Khan that the practice of turning northern land into pasture was prohibited.^[5]^{: 218–219} The Yuan construction and maintenance of the Grand Canal greatly altered the environment of the North China Plain. To maintain canal water levels and prevent water from draining into the Yellow River, Huai River, or Yangtze River, in addition to using sluice gates and weirs as barriers, people also had to redirect and block small streams and rivers flowing westward into the Shandong Peninsula to ensure all river water entered the Grand Canal. Sediment brought by the Yellow River and its tributaries would deposit in the canal, requiring regular dredging. Dense maintenance was needed at the intersections of the canal with several major rivers. The government had to invest large resources to maintain canal operations; otherwise, its water system could collapse, bringing flood disasters to the North China Plain.^[5]^: 155 After the Yuan changed the Yellow River's course, the abandoned northern channel became a source of sediment. When winds rose, sandstorms ravaged the entire North China region.^[5]^{: 196、199} During the Jin, when the Yellow River changed course southward, Juyeze lost its water source. Water receded and sand remained, creating large areas of shoals that were reclaimed by nearby residents. In 1180, the Jin government even sent envoys to recruit refugees for tuntian in Liangshan Marsh. Smaller lakes silted up into flatland even earlier.^[4]^: 91–92 During the Southern Song, officials responsible for irrigation and canal systems began worrying about upstream deforestation and noted the impact of salinization and flooding on downstream areas.^[17]^: 19

By the 14th century, the construction of the Grand Canal had changed the drainage network of the North China Plain. Newly built dikes in the Yellow River basin diverted all of the river's flow into the lower-lying Huai River.^[3]^: 39. The Yuan dynasty paid relatively greater attention to flood control in the Jianghan Plain. It prohibited polder construction around Dongting Lake, converting fields back into lakes, and reopened blocked outlets along the Yangtze that had been sealed during the Southern Song, allowing water to disperse. By the Dade era (1297–1307), a total of six outlets had been reopened.^[4]^: 98.

South China

Along the Pearl River, the Yuan dynasty not only repaired the old dike enclosures built in the Song but also constructed 34 new ones. The total length of the dikes reached 320 kilometres (200 mi), protecting about 20% of the cultivated land in Guangdong.^[5]^: 203^[15]^: 76. Out of fear of the Mongol invaders, between 1273 and 1274 many residents and clans from Zhuji Lane [zh] in northern Guangdong fled south and settled on small islands at the mouth of the Pearl River. They "intercepted" sediment and reclaimed new farmland on sandbars. These newly reclaimed areas were called "sand flats" (沙坦) or "sand fields," (沙田) new land parcels formed by silt deposition.^[15]^{: 77–78, 204}. When the sandbars gradually rose close to the water surface, people placed rocks around them to stabilize the existing sediment and trap more deposits. After building stronger enclosures, beans could first be planted on the sand flats, followed by rice. Chains of sand flats formed tens of thousands of mu of farmland, creating the Pearl River Delta. At the same time, accelerated erosion of abandoned mountainous land in northern Guangdong due to the Mongol invasion sent more sediment from the Dong River to the Pearl River mouth, speeding up sand flat formation.^[15]^: 79.

In the 14th century, formation of the Pearl River Delta accelerated further. Alluvial sandbars appeared along the coast at the mouth of the Dong River, and Xiangshan Island gradually connected to the mainland.^[5]^: 201. The Mongol invasion also caused population growth in the southwestern coastal areas of Guangdong. On the Leizhou Peninsula, people cleared large areas of tropical rainforest and mangrove for reclamation, followed by slash-and-burn practices, causing permanent damage to the local environment. Many areas turned into wasteland.^[15]^: 94–95.

Ming dynasty

North China

Before the Ming dynasty, dense forests still existed in the Great Wall region.^[9]^: 56 By the Ming, forests on the Loess Plateau were heavily damaged. In the early Ming, forests in Luya Mountain and Yunzhong Mountain in northwestern Shanxi, and Heng Mountain in northern Shaanxi, remained intact. Some damaged forest areas in the Guanzhong Qinling and Xiao Mountains also partially recovered.^[4]^: 36 After Yongle established the capital in Beijing, the Taihang Mountains became a major source of timber for the city, greatly accelerating deforestation.^[11]^: 91 As the imperial palace and urban development required wood, the government conducted large-scale logging and charcoal production. After prolonged uncontrolled official and private exploitation, the forests in the Great Wall region suffered devastating destruction. After the mid-Ming, large areas of forest disappeared. By around the 17th century, fuel and construction timber were generally in short supply.^[9]^: 56, 54

Rapid population growth led to continuous reclamation of new farmland and increased demand for daily timber, causing a sudden change. Forest areas shrank quickly. Forests in the Heng Mountains and Lüliang Mountains were successively exhausted. At this point, the massive building materials needed for the capital could no longer be obtained from the middle reaches of the Yellow River and had to be sourced from Sichuan and the Two Lakes region. Due to thorough destruction, the forests' self-renewal capacity was almost lost. The middle reaches of the Yellow River presented a continuous sight of bare mountains.^[4]^: 36 Although the Ming had policies prohibiting logging, their main purpose was to protect the feng shui of imperial tombs or to meet military and political needs. The scope was very limited and showed no genuine ecological awareness.^[9]^: 46

In North China, the opening of the Grand Canal slowed the discharge of all rivers, large and small. Sediment continued to accumulate, causing periodic flooding and waterlogging. Because the river water contained salt, waterlogged land easily underwent soil salinization, becoming uncultivable. The worst areas turned into swamps, which then bred locusts. The Beijing-Hangzhou Grand Canal further impeded the already slow-flowing Yellow River and forced the Huai River to backflow into its upper reaches.^[5]^{: 311, 309} Sediment from the Grand Canal and Yellow River frequently blocked the mouth of the Huai River, causing floods to spread into the plain. Frequent flooding covered farmland with sand and gravel, sometimes up to 7–8 meters thick. Some formerly prosperous counties with fragrant rice and abundant fish saw large areas of land salinized, turning into barren red earth where even weeds would not grow. Weeds that grew after floods became breeding grounds for locusts. Due to insufficient irrigation, agriculture was limited to drought-resistant crops such as winter wheat, sorghum, and soybeans.^[5]^{: 307–308}.

In 1578–1579, Ming official Pan Jixun managed the lower Yellow River by building earthen and stone dikes, dredging the riverbed, and unifying the Yellow River's course.^[2]^: 150 He proposed the method of "constricting the water to attack the sand," using higher and narrower dikes to accelerate flow.^[5]^: 312 Water was constricted within "lǚ dī" near the banks. His river management increased sediment at the sea mouth, lowered the downstream gradient,^[2]^{: 150–151} and diverted clear water into the Yellow River to scour silt from the riverbed. In 1579, Pan Jixun built the Gaojia Weir [zh] across the Huai River, storing clear water from the Huai and two other rivers in Hongze Lake. Continuously raising the Gaojia Weir on the eastern shore of Hongze Lake ensured the lake's water level remained higher than the Yellow River, allowing grain-transport boats to pass.^[5]^{: 312–313}

Southwest

Urban residents' demand for timber prompted mountain residents to specialize in logging and timber transport. The Yunnan-Guizhou region, previously economically undeveloped with sparse settled agricultural population and inhabited mainly by non-Han indigenous peoples, developed under Ming rule into a region increasingly dominated by Han migrants and commercialized.^[5]^{: 222, 227} The southwest had rich and diverse ecosystems. In southernmost Yunnan's Xishuangbanna, rolling mountains and dense rivers existed. The Khmu people lived deep in jungles and bamboo forests, practicing slash-and-burn agriculture (continuing into the 20th century) and domesticating elephants. The southwest originally had a healthy ecosystem with tigers and elephants frequently appearing and vast forests. Thai-speaking peoples cleared some river valleys into farmland, while other ethnic groups practiced slash-and-burn. Due to high mountains and deep valleys that were difficult for humans to access, human impact was minimal.^[5]^{: 228, 232}

From around 1400, large numbers of Han people arrived in Yunnan and Guizhou. The Ming-established weisuo and military farms spread across the southwest, with 250,000 Han soldiers beginning to farm in river valleys. Indigenous groups' wooden tools could only reclaim lighter alluvial soils in valleys and were unsuitable for the heavy soils of forested areas; they also lacked oxen for plowing. The Ming equipped Han migrants with iron plows and tens of thousands of oxen, enabling them to reclaim forest soils. In the 15th and 16th centuries, millions of mu of farmland were opened in Yunnan and Guizhou.^[5]^{: 232–233} During court wars against indigenous peoples, Han armies set fire to mountains, destroying animal habitats. The ultimate solution to rebellions was to transform different ecological environments into farmland. In Guizhou, some local tusi also led people to shift from slash-and-burn to plow-based production.^[5]^{: 234–235}.