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Ecology

The faces of the Amazon

Dry ground forests and waterlogged stretches behave differently

Some stretches of the Amazon Forest work in the opposite way to what used to be thought: the Tapajós National Forest, in the state of Pará, for example, releases more carbon dioxide (CO2) than it traps, according to recent studies carried out in the Large Scale Biosphere-Atmosphere Experiment in Amazonia (LBA), a multinational project that is little by little shedding light on the climatic and biochemical workings of the forest that covers over half of the Brazilian territory. Also known as carbonic acid gas, CO2 , produced by the breathing of living beings and by the burning of fossil fuels like petroleum, is the main gas that governs the temperature of the Earth’s atmosphere.

Another discovery from the LBA team: an area corresponding to one fifth of the Amazon – flooded forests, subject to flooding during the rainy period – emit a high quantity of methane (CH4), another gas associated with global warming, the greenhouse effect. One of the 27 studies on the LBA published in May, in a special edition of the Global Change Biology magazine, shows that the volume of methane released into the atmosphere by these areas located close to rivers and igarapés (rivulets), in the low part of the Amazon Basin, is up to eight times more than used to be thought. Analyses carried out by the team coordinated by John Melack, from the University of California, United States, indicate that the flooded forests close to Manaus, in the state of Amazonas, also release a quantity of CO2 equivalent to 40% of that absorbed on dry land.

“We did not imagine such high values of methane and CO2 emissions in these flooded areas”, comments Paulo Artaxo, from the Physics Institute of the University of São Paulo (USP), one of the coordinators of the LBA, a project with a budget of US$ 80 million that gathers a thousand researchers from Latin America, the United States, and Europe. But the emission of methane, even in such a high quantity, has not contributed towards an aggravation of global warming, because, in the overall balance, the Amazon is in equilibrium, according to recent calculations. That is to say, the quantity of greenhouse gases given off by the forest, by slash and burning, by the soil, and by waterlogged areas, is practically the same as that absorbed by the ecosystem as a whole, according to calculations published by Artaxo and Eric Davidson, from the Woods Hole Research Center, in the United States. In practical terms, the Amazon is neither the planet’s great source of oxygen, nor its great polluter.

Interactions
The findings on methane emission constitute just a sample of the 700 studies that will be presented at the 3rd Scientific Conference of the LBA, to be held in Brasilia from 27 to 29 of this month – it is the first time that so many novelties about the Amazon will be made known simultaneously. The knowledge accumulated since the beginning of the project, in 1998, is now making it possible for the specialists to have a more precise idea of how the vegetation interacts with the atmosphere and is helping to dimension the impact of the presence of man on the forest: the estimate is that 24 million persons live in the Amazon, which extends over Brazil, Bolivia, Peru, Ecuador, Colombia and Venezuela.

The workings of the Amazon Forest, which, generally speaking, seems to be homogeneous, is proving to be more complex in a closer look, to the point of varying a lot from one region to another. The Amazon is not a uniform forest, from the point of view of landscape and of chemical and physical behavior, but a mosaic of distinct landscapes, which, as a whole, form a unique design. In the rainy season, between November and April, the trees from the dry land forests absorb more carbon and grow more intensely. The new fact is that the opposite occurs in those in the flooded areas, which grow more during the dry season, according to Humberto Rocha, from USP’s Astronomy, Geophysics and Atmospheric Sciences Institute. This phenomenon is associated with the excess of water that limits photosynthesis, a process by which plants under sunlight transform the carbon absorbed from the atmosphere into long sugar molecules (cellulose), the main component of wood.

The LBA project has overturned another old concept about the Amazon: the forest suffers from a lack of nutrients. It used to be thought that only the lack of phosphorus would limit the growth of the trees. Indeed, phosphorous is the main nutrient of untouched, or primary, forests. But a study carried out in the forests of the state of Pará, showed that, in degraded areas, it is the deficiency of another nutrient, nitrogen, a chemical element that is abundant in the forest, that limits the growth of the vegetation.

“Successive burning of the forest diminishes the quantity of nitrogen, which is transformed into gas with the heat of the fire”, comments one of the organizers of the LBA conference, Michael Keller, a researcher from the International Institute of Tropical Forestry, linked to the United States Department of Agriculture. “The nitrogen literally goes up in smoke”, he says. This discovery has an application: to recover the areas degraded by agriculture or livestock, it will possibly be necessary to add nitrogen-based fertilizers to the soil, in high quantities. Just in the Brazilian portion of the Amazonian Forest, 25,000 square kilometers are deforested a year.

Oddly enough, in more evidence of how the stretches of the Amazonian Forest behave differently, the speed of the growth of the forest varies along its extension from east to west, from Pará to Colombia. According to a study from the group of Yadvinder Malhi, from Oxford University, in the United Kingdom, the forest tends to grow and to die three times more quickly in the western portion – taking in the states of Rondônia and Amazonas and stretches of Bolivia, Peru, Colombia and Venezuela – than in the eastern part. How to explain this? One of the hypotheses is that the high rates of growth are due to the fertility of the soil in the areas close to the Andes mountain range, apparently better than in the soils of the east.

Use of the land
If the lack of nitrogen in the soil creates problems for the plants of the forest, the excess of this element in the atmosphere also causes negative changes, as it can be seen in cattle ranches in the state of Rondônia. A team made up of Brazilian and American researchers collected rain water in Balbina, in the state of Amazonas, one of the areas in which the forest is most preserved, and also in Rondônia, where the vegetation has already suffered from successive clearing by burning to make way for pastures.The analysis of the samples of rainwater from these two regions showed very different results. Although the rain in Balbina contains a small quantity of nitrogen – 2.9 kilos per hectare -, found in the form of nitrate, an essential nutrient for plant growth, in Rondônia the rain brings an average of 5.7 kilos of nitrogen per hectare.

According to Luciene Lara, from USP’s Nuclear Energy in Agriculture Center, the quantity of nitrogen in Rondônia is similar to the quantity found in developed areas of the state of São Paulo. A few problems come from this: spawned from nitrogen, nitrates make the soil more acid, reducing the productivity of the plants and increasing the proliferation of algae in rivers and lakes.

There is still no way of measuring the impact of the accumulation of nitrogen in the Brazilian forests, since the damage to the ecosystem only pops up in 20 to 30 years. But it is possible to get an idea of the possible devastation. During the 1960s, the destruction of forests in Switzerland and Germany was caused by high quantities of nitrates and sulfates. “In Europe, it is simpler to measure the impact on the vegetation, since there are very, very few species of plants in the forests”, explains Paulo Artaxo. “In the Amazon, the enormous biodiversity hinders the studies of the impacts on the vegetation.”

One of the greatest challenges for the Amazon and another theme to be debated at the LBA’s conference is how to reconcile the preservation of nature with the needs of the populations that live in the forest. The federal government announced that it intends to pave the BR-163, a highway that links Cuiabá, in Mato Grosso, to Santarém, in Pará, to channel away the agricultural and livestock production, but scientists and nongovernmental organizations fear the deforestation of the Central Amazon, which usually follows road building. The fear is justified: about 14% of the Amazon Forest has already been devastated, and 10% of this area, equivalent to the state of São Paulo, has been abandoned, because the soil has become poor in nutrients or has marked erosion, or also because the small farmers had no more resources for investing in planting.

Britaldo Soares, a researcher from the Federal University of Minas Gerais (UFMG) and a member of the LBA, believes it possible to reduce by half the deforestation along the road, if, before it is built, a new strategy for occupation is adopted, including tax incentives for preservation, organization of networks of rural producers, regulatory measures for occupation, and a rigid and effective supervision. Another participant in the project, geographer Bertha Becker, from the Federal University of Rio de Janeiro (UFRJ), is also working in this area. “We can establish a new model for settlement, create conservation units, and qualify the local population for forest handling, with certification of the timber”, she comments. “It is necessary to create in Amazon opportunities for economic growth with social and environmental commitment.”

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