destruction and survival

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11SC/NATS 1840, Science and the Environment SC/NATS 1840, Science and the Environment –– VIII Destruction & SurvivalVIII Destruction & Survival

Destruction and Survival

Minoan vase showing the harvest with winnowing forks.


Agriculture is destructive to the environment.

The timing of environmental damage depended on:

The nature of the environment.How productive the soils were without destruction of the ecosystem.The population.


Natural balances are destroyed.Agriculture involves clearing the natural ecosystem to create an artificial habitat for growing plants and grazing animals.

A variety of plants and a natural ground cover are replaced by a small number of crops.Soil is exposed to wind and rain, especially when fields are left bare for part of the year.Nutrient recycling is disrupted.

Extra inputs of fertilizers are required.

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Irrigation is even more disruptive.Creates an even more artificial environment than dry farming.Adding large amounts of water to poor soil can have catastrophic long-term effects.Extra water drains into the water table.

Will cause water levels to rise until soil becomes waterlogged.Extra water also increases mineral content of soil, esp. salt.

In areas of high evaporation this can leave a thick layer of salt on the surface, making agriculture impossible.Only hope is careful irrigation, not over watering, and long fallow periods.


Villages and townsConcentrate demands for resources.

Construction materials for houses and for new and varied goods are required.

Leads to deforestation.Leads to more soil erosion around settled areas.Leads to reduced crop yields.

If obtaining the food supply became more difficult, surpluses fell and the basis of society was threatened.


Sumer

Leonard Woolley in 1936 wrote a book about Ur in Sumer. He was puzzled by the desolate, treeless landscape of present-day southern Mesopotamia.The ancient world seemed incredible, since it must have been once a verdant landscape capable of supporting a lavish culture.

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What happened?Answer: Sumerians themselves destroyed their environment.

By deforestation. And over cultivation.

In Sumer, rivers were highest in the spring and lowest in August and October when crops most needed water.

Water storage was essential.


Costs and benefits of water storage: At first, the advantages of increased yield outweighed the disadvantages.But slowly major, irreversible problems emerged.Temperatures in the summer were 40° C, leading to:

Increased evaporation.Increased salt.

Waterlogging of the soil was increased by:Low permeability of the soil.Slow drainage of very flat land.


Compounding EffectThe vicious circle:

All made worse by silt coming down river due to deforestation in the highlands.

Added 5 ft of silt every millennium.Extended delta by 15 miles per millennium.

More waterlogging brought more salt to the surface.High evaporation produced thick layer of salt.

According to present day knowledge, the only way to avoid the worst is to leave land fallow and unwatered for long periods to allow the water table to fall.

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Impossible in Sumerian societyLimited amount of land.Rising population.Need to feed more bureaucrats and soldiers.Mounting competition between the city states.Made an overwhelming requirement to grow more food.Short term demands outweighed any consideration of long-term stability.All led to increased pressure to intensify the agricultural system.


Recording their own disasterAround 3000 BCE, Sumeria became the first literate society in the world.

We therefore have records of changes in the agricultural system from back then.Early dynasties lasting till 2370 BCE were militaristic, used food surplus to feed the bureaucracy and armies.All were dependent on the agricultural base for large-scale production of wheat and barley.


Salinisation and Wheat versus Barley In 3500 BCE equal amounts of wheat and barley were grown.

Wheat can only tolerate 0.5% of salt in the soil.Barley can grow in twice this amountSalinisation of the soil can be deduced from declining proportion of wheat grown.

By 2500, only 15% of crop was wheat.By 1700 BCE no wheat was grown at all.

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Declining yieldsIn the early phase when land went out of cultivation due to salinisation, the land was replaced with newly cultivated fields.Rising population and greater demand for surpluses raised demand for more land to cultivate.

But supply was limited, even with new irrigation techniques.

Once salinisation took its toll on available land, the surplus began to fall rapidly.


Collapse of SumerIn 2370 the independent city states fell to the invading Akkadians.For 600 years the region was conquered and reconquered, finally falling to the Babylonian empire to the north.Moral of the story:

An artificial agricultural system is fragile and easily overused, causing its collapse and with it the society that depends upon it.


Deforestation Extensive deforestation has been a major problem of societies throughout history.Increasing populations put an increasing strain on local environments, and especially on wood, which has so many uses:

HeatingCookingConstruction

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And, to make matters worse…Forests were cleared for cultivation

The slow destruction of forests around all settled communities is a constant feature of their histories.

Early societies used metal axes, ring barking, and fire to clear a forest and/or obtain wood.


A slow process – Too slow to notice

No one generation would be aware of making any dramatic changes.

People accepted the process as natural.Little evidence of attempts at major replanting.Coppicing was practiced in parts of Europe to keep a sustainable crop of wood.

Over many generations, the scale of destruction could be massive.

Huge dense forests would become treeless or have only isolated patches remaining.


The Example of China About 200 years ago, all the original forests of China had been destroyed. This was one of the main causes of the flooding of the Yellow river. The Yellow River in China from the

air.

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The process can also be quick: When Addis Ababa became the capital of Ethiopia in 1883, it was surrounded by dense forest. Within 20 years, a zone stretching 100 miles around the town had be devastated – stripped of trees by charcoal burners making fuel for the capital.


The Mediterranean area now

Present landscape is olive trees, vines, low bushes, and herbs.

This is the result of massive environmental degradation brought about by long-term settlement and growing population.


Mediterranean Deforestation Natural vegetation was mixed evergreen and deciduous forest. Slowly cleared, bit by bit for land, fuel, construction materials.

Could not regenerate because of sheep, goats, and cattle grazing until terrain was reduced to inedible plants.Removal of tree cover led to serious soil erosion.

Silt brought downriver blocked water courses and caused large deltas to form.No more than 10% of the original forests that stretched from Morocco to Afghanistan in 2000 BCE remain today.

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Cedars of Lebanon

Hills of Lebanon and Syria, once famous for the Lebanon cedars.Prized by the states of Mesopotamia as building materials. Became a mainstay of the Phoenician commerce, traded over a widearea. Now only a few remnants maintained as a symbol of past glory.


Destruction in Ancient Greece Large scale destruction began 650 BC as population rose.

Problem was overgrazing on the 80% of the land that was unsuitable for cultivation. Hills of Attica were stripped bare in a couple of generations. By 590 in Athens, Solon, the reformer, argued that cultivation on steep slopes should be banned because of erosion.


Even Plato noted the deforestation Plato’s description in the Critias:

“What now remains compared with what then existed is like the skeleton of a sick man, all the fat and soft earth having wasted away, and only the bare framework of the land being left …”

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Italy Same problem a few centuries later.

Silting of rivers.Ravenna lost its access to the sea.Ostia, the port of Rome, survived by constructing new docks.

Roman Empire increased pressure on environment elsewhere to supply Rome.

Many provinces turned into granaries to feed Italy.


North Africa Growing Roman demand for grain pushed cultivation into the hills and onto vulnerable soils easily eroded. After fall of Rome, the Berbers moved in bringing grazing animals that prevented recovery of the vegetation.

Ruins of Leptis Magna, one of the great centers of the Roman Empire in present day Libya. Now surrounded by vast deserts.


Fall of Rome? Similar processes occurred in many places in the Roman Empire.

In Asia Minor, the interior of the old Roman provinces of Cariaand Phrygia were completely deforested by the 1st century.Emperor Hadrian had to restrict access to the remaining forests of Syria because of deforestation.Antioch and Baalbeck continued to flourish until the Byzantine period.

Both are now in ruins. Antioch is under 28 feet of water-borne silt from hillside deforestation.

The pressure to feed the Roman population and armies must have contributed to the fall of Rome

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Mesoamerica What happened to the Mayan civilization of Mesoamerica?


Mayan Civilization Mayan society developed in the dense lowland jungle of Mesoamerica.

Earliest settlements from about 2500 BC.Population rose slowly. By 250 BC a complex hierarchical society had developed.


Complex, technically sophisticated society

A uniform culture throughout the area arose, with complex pyramid structures supporting temples.

Existing sites have buildings aligned to significant astronomical points and stones inscribed with important astronomical dates.

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Heights of sophistication followed by sudden collapse

The golden period of the Mayan civilization was from about 600 to 800.Then within a few decades it all collapsed.

No more buildings.Population levels fell abruptly.Cities soon covered over by the jungle.

Recent evidence points to an intensive cultivation system involving terracing to control erosion and raised fields in swamps, with drainage ditches.The population continued to rise to beyond what the land could support.


Egypt Sustained balance for 7000 years.

They exploited a natural process (flooding of the Nile) rather than create an artificial system.Long term stability maintained so long as there were only limited modifications to the natural flood regime.

But there could be variations from year to year in the flood level.In the short term results could be disastrous.

In the 1840s major changes were made to the system which have had enormous consequences.


The Lure of Wealth Egypt’s problems began not with a need to feed more people but with a desire for a higher standard of living.

Artificial irrigation systems were introduced to make more arable land –

Not for food, but for cotton for sale in Europe.Permanent irrigation produced widespread salinisation and waterlogging in a few decades.

In 1882 a British agricultural expert described the soil as covered with “white nitrous salts … glistening in the sun like untrodden snow.”

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Artificial Control of the Nile Itself In the early 20th century attempts were made to control the Nile with a dam at Aswan.Present high dam at Aswan, began in the 1950s finally undermined Egyptian agriculture for good.

Looking north from the High Dam toward the old Aswan dam.


Destroying the Natural Ecosystem of the Nile

The Aswan dam retains the needed silt behind the dam. The natural fertility of the Nile valley was destroyed. Expensive artificial fertilizers are now necessary.

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