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Global Warming Causing Changes in the Amazon Rainforest?
Wed 10 March, 2004 19:01 Reuters LONDON (Reuters) - Strange things are happening in lush Amazonian rainforests and scientists said Wednesday rising levels of carbon dioxide could be the cause. Even in pristine rainforests unaffected by human activities such as logging or burning, researchers have noticed dramatic differences in the growth patterns of trees over the past 20 years. That could distort the forest's fragile balance, affecting rare plant and animal species. "The changes in Amazonian forests really jump out at you," said William Laurance of the Smithsonian Tropical Research Institute in Panama. "It's a little scary to realize seemingly pristine forests can change so quickly and dramatically." Laurance and his team, whose research was published in the journal Nature, noticed that the growth of large trees in the Amazonian rainforests have accelerated over the past two decades while the growth of smaller ones has slowed. Levels of carbon dioxide (CO2) have risen by 30 percent in the past 200 years because of emissions from automobiles and industry and rapid forest burning, particularly in the tropics. Much of the increase in CO2, which plants use from the air for photosynthesis, has occurred since 1960. The scientists suspect the rising CO2 levels are fertilizing the rainforests and increasing competition for light, water and nutrients in the soil. So the big fast-growing trees have an advantage and are outpacing the smaller ones. The researchers believe the odd change in growth patterns could also be a signal for an overall change in rainforest ecology. 'Pristine' Amazonian rainforests are changing 18:00 10 March 04 NewScientist.com news service http://www.newscientist.com/news/news.jsp?id=ns99994766 Changes to apparently pristine parts of the Amazonian rainforests have been revealed by a survey of trees. Tall, fast-growing trees are doing better than those that grow slowly. The changes - possibly the result of increasing levels of carbon dioxide in the atmosphere - threaten to reduce the Amazon basin's crucial ability to store excess CO2. The discovery comes from a study of 18 undisturbed plots in the heart of the Brazilian Amazon that researchers have been monitoring since the 1980s. Tropical ecologist Bill Laurance, of the Smithsonian Tropical Research Institute in Balboa, Panama, and his colleagues combed through census records of the plots to see how their trees have changed over time. Of 115 tree genera, they found that two became significantly more common and 14 became significantly rarer over the 15 years of the study. The winners tended to be tall, relatively fast-growing canopy trees, while the losers tended to be slower-growing trees that live their whole lives in the dim depths of the forest below the canopy. Laurance and his colleagues could find no past anomalies in rainfall that might explain this pattern of change. Nor is it due to some peculiarity of their research techniques - a second, independent set of study plots nearby showed similar changes. Dense wood Instead, Laurance speculates that rising levels of CO2 in the atmosphere may be to blame. More CO2 means faster photosynthesis. Faster growth, in turn, favours those trees that already grow fastest. "It's very difficult to predict what the long-term effects of these changes will be," says Laurance. However, because understorey trees grow slowly, they produce denser wood, which in turn means that the carbon content of each tree is greater. If the forest composition shifts away from these trees toward faster-growing genera with lighter wood, the forest will be less able to take up CO2. Many ecologists think the Amazon rainforest is one of the major "carbon sinks" that keep atmospheric CO2from rising more quickly than it already has. If anything were to interfere with that, says Oliver Phillips, a tropical forest ecologist at the University of Leeds, UK, "that's bad news". Journal reference: Nature (vol 428, p 171) Bob Holmes Astonishing Discovery over the Amazonian Rain Forest International research team has discovered huge amounts of unexpected organic aerosols over the South-American tropical rain forests Isoprene, an organic compound generated in large quantities by natural vegetation, was originally thought not to be involved in producing atmospheric aerosols. It has now been found to be a potentially major player in this process. An international team of scientists from the Max Planck Institute of Chemistry, Mainz, Germany, the University of Antwerp, Belgium, the Ghent University, Belgium, and the University of S�o Paulo, Brazil, examined natural aerosols from the Amazonian rain forest, and has found that they contained two previously unknown compounds, which are photooxidation products of isoprene. These compounds are hygroscopic and could impact cloud formation, rainfall and climate (Science, 20 February 2004). Isoprene is a volatile organic compound that is emitted in large quantities by forest vegetation. Its annual emission is estimated to be 500 million tons worldwide. But although isoprene readily oxidizes to form volatile products, popular wisdom held that it didn�t form products that could contribute to aerosol particle formation. Intensive measurements over the Amazon Basin, however, revealed the presence of two novel 2?methyltetrol compounds. These compounds are formed in the atmosphere through reaction of isoprene with hydroxyl radicals. To exclude pollution of human origin, the measurements were performed during the rainy season in a remote location of the Amazon Basin. Wind trajectories showed that the air had traveled over several thousand kilometers of pristine tropical forest before being trapped and analyzed. It is estimated that the photooxidation of isoprene results in an annual production of about 2 million tons of the new compounds. This represents between 5 and 25% of the organic aerosol formed by atmospheric photochemistry from biogenic precursors. This discovery is a breakthrough because for the first time a link can be demonstrated between isoprene emitted by forest vegetation and formation of water soluble fine particles. These aerosol particles give rise to the formation of haze and reduce the visibility in forested areas. They have an effect on cloud formation and influence rainfall and climate. Original work: Magda Claeys, Bim Graham, Gyorgy Vas, Wu Wang, Reinhilde Vermeylen, Vlada Pashynska, Jan Cafmeyer, Pascal Guyon, Meinrat O. Andreae, Paulo Artaxo and Willy Maenhaut Formation of Secondary Organic Aerosols Through Photooxidation of Isoprene Science, 303, 1173 (2004), 20 February 2004 Max Planck Society for the Advancement of Science Press and Public Relations Department Hofgartenstra�e 8 D-80539 Munich PO Box 10 10 62 D-80084 Munich Phone: +49-89-2108-1276 Fax: +49-89-2108-1207 E-mail: [email protected] Internet: www.mpg.de Responsibility for content: Dr. Bernd Wirsing (-1276) Executive Editor: Dr. Andreas Trepte (-1238) Online-Editor: Michael Frewin (-1273) ISSN 0170-4656 PDF (70 KB) Contact: Prof. Meinrat O. Andreae Max Planck Institute for Chemistry, Mainz Tel.: +49 6131 305-421 Fax: +49 6131 305-487 E-mail: [email protected] Dr. Pascal Guyon Max Planck Institute for Chemistry, Mainz Tel.: +49 6131 305-404 Fax: +49 6131 305-487 E-mail: [email protected] CONTENT COPYRIGHT REUTERS and THE NEW SCIENTIST. THIS CONTENT IS INTENDED SOLELY FOR EDUCATIONAL PURPOSES. |
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