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The stressed forest

Researchers evaluate the effects of the 2005 drought in Amazonia

DELFIM MARTINS / PULSAR IMAGENSAmazonia forest: scientists point towards between 40% and 50% risk of collapseDELFIM MARTINS / PULSAR IMAGENS

The drought that settled over the Amazon, between May and September of 2005, is worrying scientists. The fear is that the phenomenon – that dried up immense rivers, brought about the brutal death of fish and isolated various riverside communities – repeats itself during the coming years and reduces the forest’s resistance to climate changes.

Differently from other droughts brought about by El Niño, that of 2005 was the result of a rarer phenomenon: the elevation of the surface temperature of the North Tropical Atlantic Ocean and the consequent reduction of the intensity of the Northern Trade Winds, which normally bring humidity to the Amazon. And it arrived after two years, drier than expected and of a season with little rains. The effects of this drought were intensely debated at the Climate Changes and the Destiny of the Amazon Conference, which took place from the 22nd until the 24th of March at Oriel College, Oxford University, England, two weeks before the publication of the second IPCC (Intergovernmental Panel on Climate Change) report, with forecasts about the effects of the planet’s average temperature increase upon the life of people and the economy of countries.

Luiz Eduardo Aragão, a Brazilian biologist who has been working for two years at the Environmental Change Institute (ECI), at Oxford University, examined hundreds of satellite images and concluded that the 2005 drought facilitated the propagation of forest fires. It is estimated that the combination of drought and fires that spread without control had increased by 33% the average number of fire outbreaks in the Amazon. Another conclusion, elaborated in conjunction with other Brazilian, North American and English  researchers, is that the fires in the state of Acre, the most impinged upon by the drought, covered an area five times greater than the area directly deforested. The flames transformed into ashes the vegetation closest to the ground over 2,800 km² of forest – an area almost twice the size of the city of Sao Paulo -, leaving the forest more vulnerable to the impact of future forest fires.

In another period of intense drought, between 1997 and 1998, which resulted from the combination of El Niño with the warming of the waters of the North Tropical Atlantic Ocean, the flames consumed an area of forest proportionally smaller, corresponding to twice the deforested area, although it had been more widespread: leaving 67% of the the Amazon basin – equivalent to 4.3 million km² of forests – under the effect of the shortage of water. Prolonging itself through the rainy season, it intensified the forest fires especially in the State of Roraima. “The fire, which spreads more easily with a drought, became the principal element of transformation of the forest”, observed biologist Aragão.

Carlos Peres, ex-professor at the University of São Paulo (USP) who currently lectures at the University of East Anglia, detailed out this conclusion in a parallel study, realized over a nine year period in the forest areas of firm ground in the Central Amazon that had been burned up to three times. In his assessment, the so-called creeping fire could increase the mortality of trees from 10% to 45% and profoundly alter both the structure and the composition of the forest. Added to the loss of biodiversity, there is an impoverishment of the principal ecosystem functions, like the retention of biomass and carbon in the areas subject to the vicious cycle of forest fires.

Extreme episodes such as that of the 2005 drought could also deregulate the cycle of rains, essential for the survival of the forest, the animals and the region’s population, recalls José Marengo, from INPE. In fact, in the year following the drought the climate oscillated between two extremes – and the same towns and cities that had passed through four months of extreme water shortage suffered with floods equally uncommon, which could be associated to the droughts. In the estimation of Oliver Phillips, from Leeds University, England, the 2005 drought could have broken the linearity of the forest growth, evaluated by way of the measurement of the diameter of thousands of trees.

The constant fires also represent a pressure for a sudden transformation of the forest, to open up space for the agriculture and cattle raising industry or for species of plants that survive with little water.

“The Amazon is more vulnerable”, sentences Yadvinder Malhi, one of the conference organizers. The succession of intense droughts, forest fires, wood extraction and the substitution of forest for crops and pasture areas are reducing the resistance of the the Amazon Forest to the impacts of global warming. According to John Schellnhuber, the director of the Potsdam Institute for Climate Impacts Research in Germany, the risk of the forest entering into collapse, “in a not too distant future”, is between 40% and 50%. This risk would drop off to a value close to 10% if efficient rules were adopted to preserve the natural vegetation.

Oliver Phillips, who for some 20 years has been studying the forest in six countries of the region, concluded that both the growth and the mortality rate of trees have intensified. A possible result of this pressure is that the tropical dense and humid vegetation tends to be gradually substituted by another, more open, of more modest proportions and more resistant to droughts, underlined Carlos Nobre, a researcher at the National Institute for Space Research (INPE). In his assessment, this transformation implies a “tremendous erosion of biodiversity”.

The evaluation of the impact of climate changes in the Amazon will demand a dialogue between specialists from the most diverse areas. Eduardo Brondizio, an anthropologist at  the Indiana University, the United States, presented the Amazon as a mosaic of dynamic and varied social groups. He studied how small farmers from the Pará State towns of Altamira and Santarém reacted to the intense droughts such as those of 1997-98. He concluded that individual and local actions predominate, principally ruled by personal experience and by the lack of confidence in the government institutions. “Our tendency is to simplify and to encounter panaceas, but we have to learn to deal with the complexity”, he said.