Rainforests in Far East shaped by humans for the last 11,000 years

New research from Queen’s University Belfast shows that the tropical forests of South East Asia have been shaped by humans for the last 11,000 years.

The rain forests of Borneo, Sumatra, Java, Thailand and Vietnam were previously thought to have been largely unaffected by humans, but the latest research from Queen’s Palaeoecologist Dr Chris Hunt suggests otherwise.

A major analysis of vegetation histories across the three islands and the SE Asian mainland has revealed a pattern of repeated disturbance of vegetation since the end of the last ice age approximately 11,000 years ago.

The research, which was funded by the Arts and Humanities Research Council and the British Academy, is being published in the Journal of Archaeological Science. It is the culmination of almost 15 years of field work by Dr Hunt, involving the collection of pollen samples across the region, and a major review of existing palaeoecology research, which was completed in partnership with Dr Ryan Rabett from Cambridge University.

Evidence of human activity in rainforests is extremely difficult to find and traditional archaeological methods of locating and excavating sites are extremely difficult in the dense forests. Pollen samples, however, are now unlocking some of the region’s historical secrets.

Dr Hunt, who is Director of Research on Environmental Change at Queen’s School of Geography, Archaeology and Palaeoecology, said: “It has long been believed that the rainforests of the Far East were virgin wildernesses, where human impact has been minimal. Our findings, however, indicate a history of disturbances to vegetation. While it could be tempting to blame these disturbances on climate change, that is not the case as they do not coincide with any known periods of climate change. Rather, these vegetation changes have been brought about by the actions of people.

“There is evidence that humans in the Kelabit Highlands of Borneo burned fires to clear the land for planting food-bearing plants. Pollen samples from around 6,500 years ago contain abundant charcoal, indicating the occurrence of fire. However, while naturally occurring or accidental fires would usually be followed by specific weeds and trees that flourish in charred ground, we found evidence that this particular fire was followed by the growth of fruit trees. This indicates that the people who inhabited the land intentionally cleared it of forest vegetation and planted sources of food in its place.

“One of the major indicators of human action in the rainforest is the sheer prevalence of fast-growing ‘weed’ trees such as Macaranga, Celtis and Trema. Modern ecological studies show that they quickly follow burning and disturbance of forests in the region.

“Nearer to the Borneo coastline, the New Guinea Sago Palm first appeared over 10,000 years ago. This would have involved a voyage of more than 2,200km from its native New Guinea, and its arrival on the island is consistent with other known maritime voyages in the region at that time – evidence that people imported the Sago seeds and planted them.”

The findings have huge importance for ecological studies or rainforests as the historical role of people in managing the forest vegetation has rarely been considered. It could also have an impact on rainforest peoples fighting the advance of logging companies.

Dr Hunt continued: “Laws in several countries in South East Asia do not recognise the rights of indigenous forest dwellers on the grounds that they are nomads who leave no permanent mark on the landscape. Given that we can now demonstrate their active management of the forests for more than 11,000 years, these people have a new argument in their case against eviction.”

2 severe Amazon droughts in 5 years alarms scientists

New research shows that the 2010 Amazon drought may have been even more devastating to the region’s rainforests than the unusual 2005 drought, which was previously billed as a one-in-100 year event.

Analyses of rainfall across 5.3 million square kilometres of Amazonia during the 2010 dry season, published tomorrow in Science, shows that the drought was more widespread and severe than in 2005. The UK-Brazilian team also calculate that the carbon impact of the 2010 drought may eventually exceed the 5 billion tonnes of CO2 released following the 2005 event, as severe droughts kill rainforest trees. For context, the United States emitted 5.4 billion tonnes of CO2 from fossil fuel use in 2009.

The authors suggest that if extreme droughts like these become more frequent, the days of the Amazon rainforest acting as a natural buffer to man-made carbon emissions may be numbered.

Lead author Dr Simon Lewis, from the University of Leeds, said: “Having two events of this magnitude in such close succession is extremely unusual, but is unfortunately consistent with those climate models that project a grim future for Amazonia.”

The Amazon rainforest covers an area approximately 25 times the size of the UK. University of Leeds scientists have previously shown that in a normal year intact forests absorb approximately 1.5 billion tonnes of CO2 (1). This counter-balances the emissions from deforestation, logging and fire across the Amazon and has helped slow down climate change in recent decades.

In 2005, the region was struck by a rare drought which killed trees within the rainforest. On the ground monitoring showed that these forests stopped absorbing CO2 from the atmosphere, and as the dead trees rotted they released CO2 to the atmosphere.

The unusual drought, affecting south-western Amazonia, was described by scientists at the time as a ‘one-in-100-year event’ (2), but just five years later the region was struck by a similar extreme drought that caused the Rio Negro tributary of the Amazon river to fall to its lowest level on record.

The new research, co-led by Dr Lewis and Brazilian scientist Dr Paulo Brando, used the known relationship between drought intensity in 2005 and tree deaths to estimate the impact of the 2010 drought.

They predict that Amazon forests will not absorb their usual 1.5 billion tonnes of CO2 from the atmosphere in both 2010 and 2011, and that a further 5 billion tonnes of CO2 will be released to the atmosphere over the coming years once the trees that are killed by the new drought rot.

Dr Brando, from Brazil’s Amazon Environmental Research Institute (IPAM), said “We will not know exactly how many trees were killed until we can complete forest measurements on the ground.

“It could be that many of the drought susceptible trees were killed off in 2005, which would reduce the number killed last year. On the other hand, the first drought may have weakened a large number of trees so increasing the number dying in the 2010 dry season.

“Our results should be seen as an initial estimate. The emissions estimates do not include those from forest fires, which spread over extensive areas of the Amazon during hot and dry years. These fires release large amounts of carbon to the atmosphere.”

Some global climate models suggest that Amazon droughts like these will become more frequent in future as a result of greenhouse gas emissions.

Dr Lewis added: “Two unusual and extreme droughts occurring within a decade may largely offset the carbon absorbed by intact Amazon forests during that time. If events like this happen more often, the Amazon rainforest would reach a point where it shifts from being a valuable carbon sink slowing climate change, to a major source of greenhouse gasses that could speed it up.

“Considerable uncertainty remains surrounding the impacts of climate change on the Amazon. This new research adds to a body of evidence suggesting that severe droughts will become more frequent leading to important consequences for Amazonian forests. If greenhouse gas emissions contribute to Amazon droughts that in turn cause forests to release carbon, this feedback loop would be extremely concerning. Put more starkly, current emissions pathways risk playing Russian roulette with the world’s largest rainforest.”

The research was a collaboration between the Universities of Leeds, Sheffield and the Instituto de Pesquisa Ambiental da Amazonia (IPAM) in Brazil. The work was funded by the Royal Society, Gordon and Betty Moore Foundation and the US National Science Foundation.

Tipping elements in the Earth’s climate system

A team of climate experts has compiled a shortlist of nine areas in the world that are in danger of passing critical thresholds or ‘tipping points’ due to climate change. They use the term ‘tipping point’ to mean that the climate system could kick-start abrupt and potentially irreversible changes for sub-systems of the Earth system. The international team, which includes Professor John Schellnhuber of the James Martin 21st Century School at Oxford University’s Environmental Change Institute, publishes its study this week in the online Early Edition of the Proceedings of the National Academy of Sciences.

The study warns that the Arctic sea ice and the Greenland ice sheet are regarded as the most vulnerable areas. The West Antarctic ice sheet is probably less sensitive to climate change, but there is a lot of uncertainty about projections of its future behaviour. This also applies to the Amazon rainforest and Boreal forests, the El Niño phenomenon, and the West African monsoon.

Professor Schellnhuber said: ‘This is the first systematic analysis of the tipping elements issue. We have developed a mathematical formalism for describing tipping elements and we have reviewed the complete pertinent literature. We have also identified the tipping elements in the Earth’s climate systems with regard to their relevance for climate policy. One could look at this paper as a “mini-IPCC-report” focusing on tipping elements.’

The scientists warn that there may be no Artic sea-ice during summer within a few decades. As Artic sea-ice melts, it exposes a much darker ocean surface, which absorbs more radiation than white sea-ice so that the warming increases. This causes more rapid melting in summer and decreases ice formation in winter. Over the last 16 years ice cover during summer declined markedly. The critical threshold global mean warming may be between 0.5 to 2 degrees Celsius, but could already have passed. The study also says that the Greenland ice-sheet could disappear within 300 years, causing the sea level to rise by up to seven metres, if there was local warming of more than three degrees.

Given the scale of potentially dramatic impacts from tipping elements the researchers say stronger mitigation is needed and adaptation will have to go beyond the current incremental approaches. In addition the researchers are recommending that a rigorous study of potential tipping elements in human socio-economic systems should be carried out. The study was led by the University of East Anglia in collaboration with Oxford University and the Potsdam Institute for Climate Impact Research in Germany.