Eco-ruin 'felled early society'
One of Western Europe's earliest known urban societies may have sown the seeds of its own downfall, a study suggests.
Mystery surrounded the fall of the Bronze Age Argaric people in south-east Spain - Europe's driest area.
Data suggests the early civilisation exhausted precious natural resources, helping bring about its own ruin.
The study provides early evidence for cultural collapse caused - at least in part - by humans meddling with the environment, say researchers.
It could also provide lessons for modern populations living in water-stressed regions.
The findings were based on pollen preserved in a peat deposit located in the mountains of eastern Andalucia, Spain.
The researchers drilled a sediment core from the Canada del Gitano basin high up in Andalucia's Sierra de Baza region.
By studying the abundances of different pollen types - along with other indicators - preserved in sedimentary deposits, researchers can reconstruct what kind of vegetation covered the area in ancient times.
They can compile a pollen sequence, which shows how vegetation changed over thousands of years. This can give them clues to how human settlement and climate affected ecosystems.
The Argaric culture emerged in south-eastern Spain 4,300 years ago. This civilisation, which inhabited small fortified towns, was one of the first in Western Europe to adopt bronze working.
But about 3,600 years ago, the culture mysteriously vanished from the archaeological record.
"Archaeologists are convinced that something happened in the ecological structure of the area just prior to the collapse of the Argaric culture," said Jose Carrion, from the University of Murcia, Spain.
"But we previously lacked a high-resolution record to support this."
Environmental change
Before the appearance of the Argaric civilisation, the slopes of Sierra de Baza were covered with a diverse forest dominated by deciduous oaks and other broad-leaved trees.
But about 4,200 years ago - just after this civilisation emerges - significant amounts of charcoal appear in the pollen sequence. According to the study's authors, this is a sign Bronze Age people were setting fires to clear the forests for mining activities and grazing.
Not long afterwards, about 3,900 years ago, the diverse forest ecosystem disappears, to be replaced by monotonous and fire-prone Mediterranean scrub.
What astonished the researchers was the speed of this change. This ecological transformation is very abrupt, appearing to have taken place in little more than a decade.
About 300 years after this ecological transformation, the Argaric civilisation disappeared.
Climatic effect
Professor Carrion said the term "ecocide" was too strong to apply in this case. Climate must also have played a part, he explained.
There is evidence conditions were becoming progressively arid from about 5,500 years ago onwards. This is indicated by a broad reduction in forest cover, the appearance of plants adapted to dry conditions and a drop in lake levels.
But Jose Carrion added: "The climatic influence began millennia prior to the appearance of the Argaric culture.
"It's not critical to the change in the landscape we see about 3,900-3,800 years ago. What appears to be critical is the evidence of burning, which in our opinion is man-made."
The degradation of soils and vegetation could have caused the collapse of agriculture and pastoralism, the foundation of the Argaric economy.
This would have led to massive depopulation of the area.
The findings were outlined at the recent Climate and Humans conference in Murcia, Spain, and appear in the journal Quaternary Science Reviews.