Interesting, no?

Hundreds of ancient earthworks resembling those at Stonehenge were built in the Amazon rainforest, scientists have discovered after flying drones over the area.

The findings prove for the first time that prehistoric settlers in Brazil cleared large wooded areas to create huge enclosures meaning that the ‘pristine’ rainforest celebrated by ecologists is actually relatively new.

The ditched enclosures, in Acre state in the western Brazilian Amazon, have been concealed for centuries by trees, but modern deforestation has allowed 450 to emerge from the undergrowth. They were discovered after scientists from the UK and Brazil flew drones over last year.

The earthworks, known by archaeologists as ‘geoglyphs’ probably date from around the year zero.

What would be even more interesting to know is how long does it take?

That is, remove man from any particular environment around here. How long does it take to go back to “normal”? Normal meaning pretty much how it was before any men turned up?

100 years is obviously too little time, but is 500 enough? 1,000? For example, say we just stopped farming the British uplands. How long before the ancient forests are back as George Monbiot recommends?

18 comments on “Interesting, no?

  1. There are forests in the south of England that used to be Roman iron ore mines:

    There were many iron mines in Roman Britain. The index to the Ordnance Survey Map of Roman Britain lists 33 iron mines: 67% of these are in the Weald and 15% in the Forest of Dean.

    There are places in Wales that used to be hydraulic Gold mines. I think you can see remains of the waterworks but I am not sure much else has survived.

    As for the Amazon, the places that used to be farmed can often be spotted on aerial pictures because the forest is so lush. All that charcoal turns out to be good for the returning forest.

    A lot of forests have a climax species. The Coastal Redwood in California or the Douglas fir or even the common beech tree in the right circumstances will grow so tall that they shade all the other species. Killing them. So you end up with a forest of one single species. That can take centuries if not longer. Which means if you log them, a lot of other species can thrive and you end up with a more biodiverse forest. So oddly one of the markers of damage to a forest is too many species.

  2. North East USA has good examples – https://www.fs.fed.us/ne/newtown_square/publications/resource_bulletins/pdfs/2004/ne_rb160.pdf – By 1820, only 25 percent of Connecticut was forested….Forests once thought to be unlimited began to disappear and the State faced declining wildlife populations and timber shortages. Soil erosion from farms increased and silt muddied the water in creeks that once ran clear. Because of the rapid runoff of storm water, springs that previously flowed all year began to dry during the summer.
    In spite of these negative environmental impacts, farming continued to flourish until economic, rather than environmental, reasons converged to alter the landscape once again.
    In 1830, the Erie Canal opened and Connecticut’s agricultural zenith passed. Within two
    decades, the small, stony farms of Connecticut were unable to compete with the larger, more mechanized farms of western New York and the Ohio River Valley.
    Much of the farmland became exhausted and unsuitable for continuous agricultural crops and soon was abandoned. Farmers left marginal hillside farms to take city jobs created by the growth of manufacturing…

    Connecticut’s Forests Today
    Forest land dominates Connecticut’s landscape. About 60 percent of Connecticut is forested – that’s 6 out of every 10 acres.

  3. New Scientist had an article on this some years back. They looked at what would happen if London was abandoned. IIRC it was something along the lines of steel frame buildings start falling apart in 200 years, at 500 years it looks superficially like forest, but with obvious man made rubble if you look, 1000 years and you’d have to be an archaeologist to discover human traces. The river breaking its banks and returning its valley to swamp would deal with Canary Wharf and Docklands.

    For something less thoroughly engineered like the uplands, maybe 200 years to get most species of tree well reestablished, except oaks of course. You’d still find odd piles and lines of stones, from buildings and drystone walls, but they’d be overgrown. Ideally you’d want lynx and wolves reintroduced as predators, otherwise the overpopulation of deer would prevent the trees getting established.

    However, you wouldn’t get back to the status quo ante, because “normal” is time dependent. We’ve introduced loads of species that didn’t exist in this region 7000 years ago. Think rhododendrons, giant hogweed, japanese knotweed, or simply maize, amaranth, potatoes and the rest of the Colombian exchange. It would be wild but differently wild.

  4. There are a number of Bronze Age stone circles a short walk from my back door that are not going away anytime soon. The area was once covered with woodland, subsequently cut back to graze animals. Topsoil washed away and trees are forever history – ‘normal’ ain’t ever coming back.

  5. I gather it’s the biodiversity that indicates the Amazon rain forest might not be a natural feature at all. Naturally, single species would come to dominate in areas favourable to them, at the exclusion of others. That this hasn’t happened may indicate the forest was “gardened”. Supported by the ratio of “useful” plants being much higher than might be expected.
    There’s certainly historical evidence the forest was densely populated The first European explorers wrote of riverbanks lined with villages. But the genocide from introduced diseases (sometimes intentionally) & the depredations of the conquerors was close to total. Something like 95% of the indigenous people died out in the couple centuries after Columbus.
    Coincidentally, I spent much of yesterday evening being virtually present in a poor rural bario in Colombia. Thanks to live video from the g/f’s phone. Peculiar to be wandering round streets almost totally absent of cars. Local transport concentrates on the horse & cart & motorbikes. And how remarkably tidy everywhere is. They may not have much, but what they have they cherish. And something I already knew from homelife. They’re almost pathologically clean. And unfailingly polite.The place’d put a UK council estate to shame.
    And it looks like I’ll be running a building project from here. They’ve got the hands & the muscle. I’ve got the knowledge & can provide the finance. Just means coping with a 6 hour timeshift. Wonders of tech, eh?

  6. The higher bits of the British uplands are too cool and wet to support much if any tree growth. We’d need to get back to the warm years of the early Bronze Age for them to have much chance. Or we could import species that can cope: somebody is successfully growing Alaskan species on Shetland.

  7. “Topsoil washed away and …”: are you sure? British grasses are quite good at securing soil.

    Anyway, if you really want trees back in numbers on land low enough to support them, kill the deer.

  8. Tim Daw – “About 60 percent of Connecticut is forested – that’s 6 out of every 10 acres.”

    Really?

    The US has more forest now than in 1900. Which is why you should ignore all those e-mail requests not to print them out.

  9. I saw a TV series on an American flight about five years ago. “The World after humans”. Answer similar to Arthur’s.

  10. @dearieme
    They tell me overgrazing exhausted what soil there was, with leaching causing iron pans to form – ground became waterlogged and acidic. As you say, the climate became cooler and wetter, encouraging blanket bog mosses. Over time a layer of peat developed (now metres thick in places). There are two trees in my vicinity that hang on doggedly, but until global warming delivers…

  11. The Tamar valley is a good case. Not sure when the arsenic mining finished but probably only 100 years ago. Was denuded of tree cover. Today largely recovered in woodland.

  12. There is an unspoken assuption in all this that an ‘unspoiled’ landscape of trees and shrubs teeming with wildlife of many different species is somehow ‘better’ than a city like Lagos or Delhi or London or New york, also teeming with wqildlife of many different species.

    My question is: Better for who?

    I mean, few of us here believe in Gaia, even as an abstract concept, yet many of us have swallowed the value judgement that is implied by ‘cities/mines/factories bad, jungles/deserts/steppes good’ which has, become the dominant paradigm of man’s relationship with the rest of nature. (And even that formulation – man’s relationship with nature – implies that man is separate from nature.)

    The danger in all this is that as more and more of us – especially our children – begin to accept the premise that even the very existence of mankind is somehow a pollutant – even a virus – on our poor planet and that we need to be controlled.

    Then the controllers step in and before we know it, we will need a licence to breed, or even a licence to exist.

  13. Year zero? No such thing. Unless they’re using it in the metaphorical sense of “sometime just after the big bang”.

  14. My question is: Better for whom?

    A very fine author on anything to do with British woodland is Oliver Rackham. Have a google for his books. You’ll learn lots and laugh quite a bit too. I’d start with his History of the Countryside.

    He has also written on the woodland of the Mediterranean area (but only the European side, as far as I know).

  15. Depends on how closely you look, and knowing what to look for. An archaeologist would still find signs of human habitation after several thousand years, but you and I might just see a few ridges in the ground or a more than usual preponderance of stones in a field.
    It never goes back to normal, just a new normal.
    As has already been said upthread, we and our cities are part of that normal.

  16. In the southeastern U.S., succession takes about 70 years. From plowed field to mature hardwood forest.

    Man-made structures could take centuries to be absorbed by the environment.

    The drones over the rain forest story is a bit hokey. The scientists just happened to be out flying their drones around the rain forest one day . . . .

  17. Gamecock,

    Archaeologists do actually do aerial surveys for the hell of it – albeit they (like most people) know full well that the Amazon used to host a number of densely populated areas, and that deforestation makes it easy to spot archaeological traces from the air. So, knowing this, it would be entirely logical for archaeolgists to just go and see what they can spot. Had a flatmate who was doing a PhD on the Sahel using the same logic.

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