Civilisation collapse as a result of ecological mismanagement may not be new
Lance
Floods brought the Nazca to their knees — but they crippled themselves
by over-farming first.
Lizzie Buchen
The mysterious Peruvian culture that preceded the Incas had a
significant hand in its own catastrophic collapse, new research
suggests.
The Nazca people are thought to be responsible for the enormous
drawing or geoglyphs etched into the deserts of southern Peru, known
as the Nazca lines. Around 500 AD, archaeological evidence indicates
that the then-flourishing society came to a sudden and bloody demise.
A leading hypothesis for this precipitous collapse proposes that
massive floods destroyed the society's agricultural system, causing
the society to fragment and feud over abruptly scant resources. But
archaeologist David Beresford-Jones of the McDonald Institute for
Archaeological Research at the University of Cambridge and his
colleagues found that — although such flooding did occur — the Nazca
brought on their own demise by logging trees to make way for farmland.
Their findings appear in Latin American Antiquity1.
"Dramatic climactic events are always used to explain culture change
in the Andes," says Beresford-Jones. "But this is not satisfying based
on what we know about human culture. It paints a picture of culture
sitting there, not changing, hit by events over which they have no
control. But Native Americans did not always live in harmony with
their environment."
Cultural forensics
Ice-core records suggested that severe storms — a mega El Niño — hit
the Peruvian Andes around the time the Nazca's fall began2, but this
had not been corroborated in the coastal valleys where the Nazca once
lived. Beresford-Jones and his colleagues, focusing on the lower Ica
valley, solidified this evidence when they discovered a flood layer
that sat directly on top of a Nazca rubbish dump. The authors then
recreated the flood using a computer simulation, demonstrating that a
flood that left such a layer could have caused the damages to the
Nazca canal system known to have occurred around 500 AD.
"But that's not the end of the story," says Beresford-Jones. "The
landscape was only exposed to the effect of the El Niño because of
what the Nazca were doing to their river valleys."
Preserved tree trunks are scattered across the now-deserted lower Ica
valley, about 200 km south of Lima, indicating a significant landscape
change. To investigate this further, team member Alex Chepstow-Lusty
of the French Institute of Andean Studies in Lima analyzed the pollen
that had been blown to the edges of the basin by strong winds. For
much of the older portion of the record, the pollen came from riparian
trees, like huarango, which once created woodland oases that lined the
rivers in the otherwise desert landscape.
But as Chepstow-Lusty moved forward in time through the pollen record,
he found a gradual decrease in huarango pollen and a concomitant
increase in pollen from agricultural sources, like cotton and maize,
indicating that the Nazca were cutting down woodland to make room for
farms. The records show that agricultural plants dramatically
disappeared and were replaced by weeds; eventually the weeds died and
the land became the lifeless desert it is today.
Beresford-Jones says that when the Nazca cut down the trees they
destroyed the root system that had been anchoring the landscape.
"When the El Niño came it cut into the floodplain because it was no
longer supported by woodland. That caused erosion and made the
irrigation system useless," he explains. "Storms like this should have
just replenished the water table and wouldn't have hurt them, but [the
Nazca] exposed their own land."
Beyond the lower Ica
"The study is original in lots of ways," says Warwick Bray, a retired
archaeologist formerly at University College London. "They've brought
to bear pollen analysis, geomorphology and archaeology all together in
one programme. There have been hints of [vegetation changes] all
along, but this is the first time all these techniques have come
ogether for southern Peru."
But Bray points out that the findings don't necessarily apply to the
collapse of the entire Nazca culture. "They were spread over several
southern coastal valleys, each with slightly different topography and
geological possibilities," he says. "This is a marvellous study of a
small region, but how much we can extrapolate across the whole range
of the Nazca no one knows."
Beresford-Jones agrees that there are considerable variations among
the valleys. "But the cultural and ecological changes we record in the
lower Ica Valley seem to correlate with the wider social changes
recorded by archaeology," he says. "It seems reasonable that our lower
Ica Valley results include some lessons for those wider changes."
The findings don't bode well for today's southern Peruvian valleys,
says Beresford-Jones, where people are removing the last remaining
riparian forests for charcoal.
"Populations have exploded, resulting in tremendous pressure upon
water resources, agricultural production and the fragile biomes, all
of which increases vulnerability to climatic perturbations such as El
Niño," he warns. "History repeats itself."
References
Beresford-Jones, D.G. et al. Latin American Antiquity 20, 303–332
(2009).
Thompson, L.G. et al. Science 229, 971–973 (1985). | Article | PubMed
Source: Nature
http://www.nature.com/news/2009/091102/full/news.2009.1046.html
Dave Smith
I understand Jared Diamond's book "Collapse" contains many similarly
cautionary case studies -- though I haven't read it.
Dave Smith
Lance
Yes - I read it a while back and probably need to refresh my memory. I
understand that many criticisms have been directed at that book which
conentrated on Easter Island (iirc). So the study reported in Nature
with its careful assessment of available evidence lends some weight to
Diamond's position.
Lance
Peter Brooks
http://en.wikipedia.org/wiki/Aral_Sea
Easter Island is a little unfair as an example - it's a very long way
from anywhere, so to keep the place viable with only canoes as
transport was never going to be easy.
Peter Brooks
I posted that a little early - probably the best, and biggest, exmple
is the Sahara.
Lance
I'm too ignorant to be sure in making this comment but I think the
issue relates to the detail of the proof that it is human activity
that was involved rather than some natural process. The article I
posted had gathered considerable evidence from a variety of sciences
to reach its conclusion. Is the same detail available for the Sahara?
Lance
Peter Brooks
gives some evidence. I'm not sure if it is the same level of detail.
A fairly recent New Scientist article contained research evidence that
deforestation was best achieved by removing forests near the coast -
causing die-back in-land.