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Peak Wood and the Bronze Age

• April 12, 2010 • 8:00 AM

The Mycenaean world was built on a solid base of bronze, but that edifice was found to have wooden feet.

E ver since humans began relying on fire, fuel became paramount to their survival.

When using metals, fire and the fuel required to feed the flame took on great significance since most metals come from ores, and it takes heat — and lots of it — to remove the metal from its parent stone. The discovery of copper smelting and bronze production — mixing copper with tin to make a harder metal — had a powerful effect on human society for thousands of years.

The alloy made weapons and tools much stronger and more durable than its wood, bone or stone antecedents. The Mediterranean world, when the heroes of Homer roamed its lands, depended on the availability of bronze for work and war.

Copper ranks as the primary component of bronze. In the Mediterranean, the greatest known source of copper lay in Cyprus. Lots of trees also grew on the island, and those trees supplied the fuel, in the form of charcoal, which turned ore from worthless stone to valued metal.

A Series From Miller-McCune

The author of “A Forest Journey: The Story of Wood and Civilization”, writes a series for Miller-McCune on the world’s first energy crisis: peak wood.

Part I: The Tree That Changed the World. Read it here.

Part II: Wood and Civilization. Read it here.

Part III: Peak Wood and the Bronze Age

Part IV: Peak Wood Brings on the Industrial Revolution and the Age of Fossil Fuels.

As its Mediterranean neighbors prospered, Cypriot copper furnaces proliferated to meet their demand for bronze. Major slag dumps serve as evidence of the extensive metallurgical activity between 1300 and 1000 B.C.

The increase in metallurgical activity put a great burden on the island’s woods. Some 120 pine trees were required to prepare the 6 tons of charcoal needed to produce one copper ingot shaped roughly like a dried ox hide and weighing between 45 and 65 pounds. One ingot, therefore, deforested almost four acres.

One shipload consisted of two hundred ingots, which cost the island almost 24,000 pines. Trade with the mainland consisted of many such shipments, so much so that the regional copper trade deforested 4 to 5 square miles of woods annually.

But the benefits of the trade were attractive. As the copper industry grew, so did the island’s standard of living. A wealthier citizenry demanded more ceramics, better heating, tastier foods and greater living space — and that all took its own toll on the woods. The combined need for fuel, for human demands and for smelting removed 10 square miles of forested land per year. Within 100 years, the 3,500-square-mile island probably lost about a third of its trees or most of its accessible woods. The change in flora was reflected in Cyprus’s fauna: Pigs, who thrive in a moist, woody environment, gave way to goats, who flourish in a more barren landscape.

As wood became scarcer, smelters made technological changes to conserve fuel. Late Bronze Age Cypriot metalworkers exposed the mined ore to the evening moisture to leach impurities rather than remove them in an initial roast, saving a third of the fuel formerly used. In another move to save fuel, people collected old and broken tools for re-smelting into new ingots. Underwater archaeologists found scrap metal aboard a ship involved in the bronze trade, indicating a lively recycling business during the period when trees became scarcer.

Despite such modern-sounding strategies, it was too little too late, and Bronze Age metallurgists could not sustain the high level of production of the previous two centuries. Copper production peaked around 1200 B.C. and the last copper furnaces were shut down in 1050 B.C. The collapse had nothing to do with the lack of raw copper feedstock. A thousand years later, after the woods had grown back following the abandonment of copper production and reserves set up by local kings, the Romans reopened the mines and produced more copper than ever before.

The decline of Cyprus’ Bronze Age copper industry due to wood shortages had a ripple effect on the great Mycenaean society and its economy. Documents of the period speak of a large number of bronze smiths in the port city of Pylos in Messenia, on the southwestern projection of the Greek peninsula. In normal times, they turned tons of bronze into weapons and tools. But when the export of bronze from Cyprus dropped precipitously, a third of them had no metal to work with and the remaining smiths received minute quantities, ranging from 3 to 26 pounds.

As John Chadwick, one of the modern decipherers of these documents, points out, “The evidence is clear. There was a shortage of metal, or this careful rationing would hardly have been necessary.”

Another document from the period orders local officials to provide “temple bronze as points for spears and javelins.” Despite their likely worn-out and tenuous state, these artifacts held great religious significance and only a grave emergency would have forced the rulers to have such sacred objects collected as material for recycling into weaponry.

With so little of society’s principal metal available, life as the Messenians had become accustomed came to a standstill. Productivity in agriculture dropped considerably without replacements for broken or worn out plows and scythes. Lacking new carpentry tools slowed down the construction of ships for commerce and war. Warriors without sufficient arrows or spearheads or armor or blades could not fight a better armed foe. Taking advantage of Messenia’s privation, insurgents overpowered those protecting the palace and destroyed it. The wealth of the entire region disappeared as did the majority of its population.

Events at Messenia presaged the catastrophes other societies in the Mediterranean would soon face. Just as the abundance of bronze gave these civilizations the material basis to grow to new heights, its paucity no doubt helped life as they knew it to collapse.

In this sea of sorrows new hope for future generations arose. Ore in Cyprus contained more iron than copper. Since metallurgists sought copper rather than iron, they ignored the slag which contained the latter. When fuel became scarce, those remaining in the metal business found they could manually remove the iron from the slag. Success in working with iron at this early stage laid the foundation for the coming of the Iron Age, and with it ultimately the fuels that would usurp wood.

John Perlin
An international expert on solar energy and forestry, John Perlin has lectured extensively on these topics in North America, Europe, Asia, and Australia. Perlin is the author of A Forest Journey: The Story of Wood and Civilization as well as From Space to Earth: The Story of Solar Electricity. Perlin mentors those involved in realizing photovoltaic, solar hot-water, and energy-efficiency technologies at the University of California-Santa Barbara, and coordinates the California Space Grant Consortium as a member of UCSB’s department of physics.

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