How does deforestation lead to floods

The age of agriculture

Even if the hunters and gatherers have influenced their environment and may have exterminated many large land animals when they conquered the world (see here), this influence was small compared to what is to come due to the small number of people before the invention of agriculture should. The triumphant advance of agriculture led to the large-scale redesign of the landscape, which increased with the founding of cities and states, with craft, trade and science and experienced a further boost with the colonization of the world.

The spread of agriculture led to nature through Cultural landscape
(In the picture: a meadow in Mecklenburg-Western Pomerania) was replaced. Photo: Ch. Pagenkopf,
from wikipedia commons, license: cc-by-sa 3.0.

If we take a look at the age since the invention of agriculture, we recognize some overarching developments that have allowed humans to secure an ever larger share of the earth's energy and material flows. These are:

  • New energy sources: The taming of animals created a new source of energy that humans could use, oxen and later horses took on driving tasks in agriculture and mining as well as transport tasks. In the end, this energy source exceeded human energy consumption many times over. In addition to animals, humans were also used as a source of energy: the great civilizations of Rome, China and the Middle East kept slaves. The usability of the old fuel wood was increased by charring it in almost airtight piles to charcoal, which reached the temperatures necessary for melting metals. This energy was later supplemented by water mills and windmills, which were not only used to grind grain, but also to dewater mines, crush ores and forge iron. The wind power was also used for transport (sailing ships). (more)
  • New tools and specialization: The effectiveness of new energy sources was increased by tools that could make better use of them. With the wooden plow, for example, the performance of oxen and horses could be significantly increased (more). The use of different tools by humans also resulted in humans doing a wide variety of things - the resulting specialization increased the effectiveness of human efforts; and led, among other things, to even better tools.
  • Trade: The ecological sustainability of a region is often limited by a limiting factor; a limitation that trade can overcome. For example, if a region had minerals but no good soil, it could trade with other regions that had fertile soil but no minerals. So both regions were able to maintain human societies.
  • Use of mineral resources: The mining of mineral resources began as early as the age of agriculture, such as ores, which enabled the manufacture of better - more metallic - tools - and also of coins, which in turn made trade easier.

These developments had consequences for the environment:

A natural landscape becomes a cultural landscape

With the invention of agriculture, people settled down and their influence was concentrated on a limited living space, where it became much stronger: material for building houses and wood for cooking and heating was taken from the environment; When arable farming advanced into previously forested areas, the forests were cut down and later swamps and other wetlands were also drained in order to be able to practice agriculture on the areas obtained in this way. With the keeping of domestic animals, litter and fodder were obtained from the forests or the cattle were driven to pasture in the forest.

Change in land use over the past 300 years: The amount
of arable and pasture land is about 40 percent of the total
The surface of the earth has increased. Fig. According to Spekrum der Wissenschaft 4/07,
Page 29; see also here.

The destruction of the forests was a gradual process, no generation has noticed any great changes; The lack of (metal) tools initially stood in the way of large-scale deforestation. But also the slash and burn over hundreds of generations had a clear impact. From the areas of origin, agriculture spread along easily usable, moist soils on rivers and lakes. Thanks to agriculture, the population increased, and in less good years soil that was not so good was also cultivated. Forest had previously stood on all of these areas. In the course of time, metal processing was also invented (see here), which on the one hand required large amounts of wood for the production of charcoal, on the other hand made metal tools possible, with which an ever larger portion of the natural landscape was finally converted into a cultural landscape in which those plants predominated that man wanted. Plants were grown far beyond their original range; Wild herbs followed them - one of the immigrants here in Central Europe is the poppy, for example. The extent of deforestation can be clearly seen in the Mediterranean region - even in Roman times, in the words of the Roman geographer Strabo, a squirrel could cross Spain from the Pyrenees to Gibraltar without touching the ground; today, large parts of the countries around the Mediterranean are treeless (see the example of Andalusia). The once famous cedar forests of Lebanon and Syria, whose wood was a highly sought-after commodity in the times of the Phoenicians, also disappeared. Deforestation for iron smelting has also reached a considerable extent in Africa. It is estimated for the entire world that before industrialization began, between 7 and 8 million square kilometers of closed forest were cut down, plus another 2 to 3 million square kilometers of open forest and scrubland, a total of almost 30 times the area of ​​Germany. This forest destruction may already have influenced the earth's climate (more).

Even before industrialization, 10 million square kilometers of forest had been cut down.

But the destruction of the forests was not the only transformation from natural to cultural landscape. Most of the origins of agriculture were in arid regions (where the particularly suitable grasses were found); here people soon recognized the yield-increasing effect of irrigation (see also The First States). The large irrigation projects also converted land into arable land. The most profound transformation was the terracing of rice fields in what is now China and Bali, beginning around the turn of the ages; or the creation of floating cultivation areas on the shores of shallow lakes by the Maya in Central America. Other wetlands have been drained to make land available for agriculture (e.g. large parts of the Netherlands); and so they became Wetlands after the forests, the second big loser in agriculture.

Web tip: Current mapping projects to show the human impact on the earth are presented in a contribution by Spiegel online.

Land use in Central Europe

In Central Europe, the early arable farmers preferred to use the loess sites. About 5,000 years ago, the first more intensive clearing of the forests began; around this time there were also the first villages (see also here). The main grain was emmer; in the north, livestock farming probably played a more important role than agriculture. It is calculated from bone finds that 60 to 80 percent of the meat consumed came from beef. In the Bronze Age, which began in Central Europe around 4,200 years ago, large areas of forest in the low mountain ranges fell victim to the procurement of fuel for the smelting industry. With the Iron Age and new inventions such as the plow, agriculture could also be extended to loamy soils; Wheat and barley, legumes, hemp and flax were now grown. After the end of the Roman Empire, the population density in Central Europe decreased again; this probably has to do with the climate that was getting cooler at the time. At the end of the migration period, more than 90 percent of the area in Central Europe was covered with forests.

In the Middle Ages the continuous expansion of agriculture began, which lasted until the end of the 13th century. Now the actual destruction of the forests in Central Europe took place: their share fell to 20 percent of the area, which was also used intensively. They were only preserved in higher mountain areas, as were moors and marshland as well as the flood-prone river plains. At that time, Central Europe seems to have reached the limit of its carrying capacity, with just two hectares of arable land available per capita. The late Middle Ages with its “little ice age” brought years of shortage and famine. The undernourished people were then easy victims of the plague epidemic from 1348 to 1350, it reduced the population density by about a third; many settlements were abandoned. The forest area increased again to around 45 percent of the land area. After this time, new forests were cleared again: the population increased again, and there was also the need for wood from glassworks, brickworks, salt extraction and charcoal burning. The forest area eventually leveled off at around 30 percent, which is roughly today's value.

Environmental impact

Soil erosion

The deforestation of the forests exposed the soil to erosion: Heavy rains could now erode the soil that was previously protected by trees. The forests had ensured that soil erosion had previously only played a role in high mountains or in deserts; with agriculture it became a widespread phenomenon that endangers agriculture itself (see also The endangerment of the soil). Soil erosion could have contributed to the extinction of the Maya civilization: the Maya settlements were in places with fertile but erosion-sensitive soils. With the forest gardens, the Maya developed an adapted agriculture, but as the population increased, this system was apparently overwhelmed: Too many forests were cut down, erosion began and mud changed the irrigation system. When droughts came along (which could also be caused by the deforestation), the end of the Maya was sealed.

Leaching of the soils

Agriculture also changed the soil directly: organic matter and minerals were removed from them with the harvest. If they were not fed back through fertilization, the soils became impoverished. Soil lack of nutrients was probably the pre-industrial environmental problem for humans! In the vicinity of the places the organic material was returned to the fields; densely populated China developed a system of faecal use, which was provided in containers in the cities and transported away at night (which is why they were also called “night soil”). In some regions, solutions developed that worked for thousands of years, even in sensitive areas: One example is the horticultural system that the Chinese developed in the loess plateau of northern China and that worked for 4,700 years. Sustainable agriculture also developed in the valley of the Nile, which was fertilized by mud from the annual Nile floods. (Also, after the flood, the water table fell fast enough to avoid salinization like in Mesopotamia.)

Floods and floods

With deforestation, the water cycle also changed: more water seeps away on pastures and fields than in forests, so that the groundwater rose and the rivers carried more water, which in total increased the runoff - it is estimated that it doubled in Central Europe from the wooded 6th century to the poorly wooded 14th century. In addition, there was hardly any flooding outside the mountains in wooded Central Europe; Floods are therefore also a consequence of agriculture in many regions. The most catastrophic flood in history was the “millennial flood” of 1342, which affected all major rivers in Germany and brought much higher discharge than the “flood of the century” on the Oder (1997) and Elbe (2002, 2006) - at that time it was also historically the smallest Forest share reached in Germany.

The effects of deforestation in densely populated China were particularly drastic: in northern China, millet was grown on a loess plateau that was easily eroded once the forests were cleared. Huge amounts of sediment got into the Huang Ho - the “Yellow River”, so named because of the color of the sediments. The sediments were deposited in the lower reaches, which caused the river to change its course several times and the devastating floods cost many people their lives.

The early protection of the forests

The fact that forest destruction can lead to flooding has of course been noticed earlier, and consequences have sometimes been drawn: in mountainous Japan, for example, in the 17th and 18th centuries, the clearing of forests on steep slopes was banned and deforested slopes were reforested . Back then, the foundation for the “green islands” was laid - today, over two thirds of its area of ​​Japan is covered by forests.

In Europe, on the other hand, hunting was often behind the protection of forests: hunting became a popular pastime for the nobility, and forests were protected for this purpose. London's St. James Park and Hyde Park, for example, go back to royal hunting forests.

Soil salinization through irrigation

Most of the origins of agriculture were in arid regions (where the particularly suitable grasses were found); here people soon recognized the yield-increasing effect of irrigation (see also The First States). However, irrigation can have catastrophic long-term consequences: If the groundwater level rises as a result of irrigation, a lot of water evaporates - the salts contained in the water remain in the soil. In arid regions, a white layer of salt can build up on the surface, ultimately ending agriculture there. When the British archaeologist Leonard Woolley began his excavations in Mesopotamia, he wondered how this barren land in his day could have produced such a great civilization. The reason is probably salinisation. This is indicated, among other things, by cuneiform tablets, which reported that “black fields turned white” and “plants were choked on salt”. This salinization is also reflected in the increasing importance of the more salt-tolerant barley: 5,500 years ago wheat and barley were grown in equal quantities, 4,500 years ago barley accounted for 85 percent and 4,100 years ago only barley was grown.The total production volume was also high, by two thirds in the period from 4,400 to 3,700 years ago. The historical events had long since shifted to the north, where agriculture was less dependent on irrigation thanks to rain.

Also the Indus culture Presumably suffered from salinization - since their writing has not yet been deciphered, fewer details are known than for Mesopotamia. In addition, there was strong deforestation there for the establishment of fields and firewood (among other things for drying mud bricks): This deforestation promoted flooding and erosion. A lack of food surpluses made it impossible to feed enough soldiers - the Indus culture was defeated by the Aryans 3,900 years ago (more).

A message from Easter Island

There was once a great culture on Easter Island, located in the middle of the Pacific: Its stone figures still attract tourists today. When the Europeans discovered Easter Island, this culture had long since perished: It had cut down its livelihood, the palm forests, and was now trying hard to stop the loss of soil with stones in the fields. Even in the age of agriculture, man was already able to saw off the branch on which he was sitting ...

die out

The destruction of their habitats also affected the original flora and fauna. The disappearance of the large animals that needed large habitats was particularly noticeable: in ancient Egypt, elephants, hippos and giraffes had disappeared from the Nile valley as early as 5,000 years ago, before the turn of the century tigers in Mesopotamia and lions and leopards from Greece. In Europe, with the spread of agriculture in the Middle Ages, aurochs and bison died out, and predators such as wolves and brown bears were pushed back into inaccessible mountainous regions.

Climate factor agriculture?

It is possible that humans have already profoundly changed the climate with agriculture - at least that is the thesis of the emeritus environmental scientist William F. Ruddiman. According to this, deforestation for agriculture is responsible for the fact that the carbon dioxide content of the air has risen slightly for 8,000 years, contrary to the natural trend (which is determined by the wobbling of the earth's axis); and that the methane content has also been rising for 5000 years (also contrary to the natural trend), is mainly due to the flooding of fields for rice cultivation in Asia. According to Ruddiman, humans have been influencing the climate for 8,000 years; without this influence the earth would be almost 2 ° C cooler, and a new ice age would probably have begun long ago. According to Ruddiman, it was not the “long summer” that made the triumphant advance of agriculture possible, but the triumphant advance of agriculture led to the “long summer”.

The fur trade

The Romans had already traded with nomadic peoples in what was later to become Russia in order to get furs from these areas. The fur trade only gained importance in the Middle Ages: When the forests of Central Europe were converted into arable and pasture land, the large forests in the north and east became a source of furs. The Vikings had traded in Kiev since the 9th century, and furs also made up a significant proportion of the trade in the Hanseatic League. The hunt for fur animals was so intense that it was soon no longer worthwhile even in the Russian forests, and so the previously largely and unknown Siberian forests were opened up (more). At the end of the 18th century, the Siberian forests were also largely exploited, so that furs were captured on the North Pacific islands.

The age of discovery

When the European conquerors, who came from centuries-old agricultural regions, discovered new countries and continents - a development that, from an ecological point of view, was driven by the convergence of large populations and scarce resources in Europe - they were surprised by the abundance of game there. Game and birds were a welcome source of provisions for them, and so the discovery was usually followed by a wave of extinction. The best-known example is the extinction of the dodo in Mauritius, a one meter tall, flightless bird that did not survive its discovery for 100 years.

Trapping and the fur trade also played a role in North America, which began soon after the discovery. The pattern corresponded to that in Eurasia: If an area was exploited, the trappers and traders moved on, and the fur trade became the engine of the development of the American West (more). By the late 18th century, fur animals became so rare in America that exports declined. A delay brought the development of the west to the Pacific coast as a result of the expedition of Lewis and Clark in 1805, the new areas were rich in beavers and otters. But by the middle of the 19th century, hunting was hardly worthwhile in North America. As an alternative, the seal hunt began. Initially, the southern fur seals of the southern hemisphere were hunted intensively in the 1780s - 1820s, when these became rare, harp seals and northern fur seals came along in the North Atlantic. (In addition, after the whales became rare, elephant seals were also hunted for their trans.) The fur seals are now under protection, while harp seals continue to be hunted to this day, especially on the northeast coast of Canada. In the countryside, the fur trade covered South America (chinchilla) and Australia (platypus, opossum and various wallaby species); When these areas were also exploited, only mink breeding remained: this is the source of most of the furs that are still traded today.

For the effects of hunting see also: A little history of whaling, and for example the bison and the pigeon in North America: A little colonial history of the USA.

The animals brought by the Europeans also contributed to the destruction of the flora and fauna. Especially pigs feral and spread in the woods (see also here); in Australia, for example, there are over 20 million wild pigs today. A famous example is the introduction of the rabbit in Australia: the rabbits brought into the country in 1859 became millions of animals within a few decades, which led to considerable crop losses. Australia tried to prevent the spread of the plague with a rabbit fence that ran across the continent and failed with several eradication campaigns. The unintentional introduction of mice and rats on the ships of the conquerors had similar consequences, for example Peru was exposed to a veritable plague of rats as early as the 1570s.

The pathogens brought with them caused great damage not only to humans (more) but also to nature: In 1889, Italian troops brought the rinderpest pathogen to Africa, where it devastated pasturage - around two thirds of the Maasai died of starvation as a result. In America, the American chestnut was almost extinct after a fungus was introduced from Asia in the form of Chinese ornamental chestnuts, which causes the "tree bark cancer". In the middle of the 19th century, the American phylloxera was introduced to Europe and led to dramatic devastation in European viticulture.

Pollution in pre-industrial cities

The cities had their own environmental problems, the most important of which were the supply of water, sewage, waste and smoke from fireplaces. Cities could only emerge where there was sufficient water available. But even the first cities in human history used their rivers to easily dispose of waste. Human feces, urine, dead animals, Waste - everything ended up in the water. The price was high: polluted water could contain pathogens, and then it meant illness and death. The connection did not escape the people, and already 4,600 years ago sewer systems can be found in the area of ​​the Indus culture. Also in the Bronze Age Minoan culture on Crete there was apparently a sewer system, the ancient Egyptians were already familiar with the sewage system. Most of all, had to Drinking water supply and sewage disposal are separated, so in many cities the water from the surrounding area was used; The Minoan aqueducts are one of the oldest examples of this, and the Roman aquaducts are the best known. Later lead water pipes were used (in London e.g. from 1236) or open pipes made of wood (Breslau from 1479). Public wells were supplied with the water, from which the residents fetched their water.

In Asia, the cities looked better: European travelers in the 18th century were amazed that the residents of Beijing did not throw their rubbish on the streets, but collected it in buckets. These were used for fertilization in agriculture, which got valuable nutrients back (see above; but also ensured that worms and parasites could use a closed cycle: at the beginning of the 20th century, 90 percent of the Chinese suffered from worm infestation). The Aztecs also collected feces for agriculture.

In addition to the waste, the cities produced considerable amounts smoke. Open wood fires and the (more) use of coal, which began in England in the Middle Ages, ensured that a cloud of smoke hung over the cities in winter. As early as 1307, the burning of coal was banned in London (where hardly anyone stuck to it due to the lack of other fuels); the smoke in the cities caused eye and lung diseases.

In addition to these environmental problems, there were those of economic activities: tanneries, for example, produced considerable amounts of acids, lime, alum and oil, which ended up in the rivers with the remains of the animal hides that could not be used.

The environmental impact of mining

Mining not only needed enormous amounts of wood to smelt the ores, it also devastated the landscape (especially since opencast mining was the main activity in pre-industrial times), polluted the air and poisoned the water. The father of mineralogy, the naturalist Georgius Agricola, also had these consequences in his De Re Metallica from 1556. Even today, one can measure the copper emissions from the introduction of copper coins in the Mediterranean area, the lead emissions from the Roman era and from the copper smelting of the Chinese Song dynasty in the ice sheet of Greenland. The Ashio copper mine, which opened in 1610 and supplied Japan with a large part of its copper during the Tokugawa period (1603 - 1868), is an example of pre-industrial wastewater pollution: the wastewater poisoned the Watarase river, which in turn poisoned 40,000 hectares of land during floods.

The impact on humans

In addition to the health consequences, the changes in the age of agriculture - as it did later during the Industrial Revolution - also had an often overlooked effect on people: the change in being also has an impact on consciousness. The division of labor, which cuts many people off from basic life support activities and makes them dependent on society's distributive systems, subtly promotes conformity and subordination; the use of money promotes quantified thinking and an attitude that values ​​natural resources and other people according to their usefulness; the technique of writing promotes the ability to think abstractly, but reduces the confidence in one's own memory. A spiritual decoupling of man from his biological roots began.

See also:
Industrial agriculture
The environmental impact of industrial agriculture

Continue with:
The union of humanity

© Jürgen Paeger 2006 - 2020