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Soil Nutrients Shape Tropical Forests, Large-Scale Study Indicates
Life Sciences Editor Champaign IL (SPX) Jan 12, 2007 Tropical forests are among the most diverse plant communities on earth, and scientists have labored for decades to identify the ecological and evolutionary processes that created and maintain them. A key question is whether all tree species are equivalent in their use of resources - water, light and nutrients - or whether each species has its own niche. A large-scale study by researchers at the University of Illinois at Urbana-Champaign and eight other institutions sheds some light on the issue. It indicates that nutrients in the soil can strongly influence the distribution of trees in tropical forests. The finding, published this week in the Proceedings of the National Academy of Sciences, challenges the theory that at local scales tree distributions in a forest simply reflect patterns of seed dispersal, said James W. Dalling, a U. of I. professor of plant biology and a principal researcher on the study. The study evaluated three sites: two lowland forests, in central Panama and eastern Ecuador, and a mountain forest in southern Colombia. The researchers plotted every tree and mapped the distribution of soil nutrients on a total of 100 hectares (247 acres) at the sites. The study included 1,400 tree species and more than 500,000 trees. The researchers compared distribution maps of 10 essential plant nutrients in the soils to species maps of all trees more than 1 centimeter in diameter. Each of the sites was very different, but at each the researchers found evidence that soil composition significantly influenced where certain tree species grew: The spatial distributions of 36 to 51 percent of the tree species showed strong associations with soil nutrient distributions. Prior to the study, the researchers had expected to see some influence of soil nutrients on forest composition, but the results were more pronounced than anticipated. "The fact that up to half of the species are showing an association with one or more nutrients is quite remarkable," Dalling said. "Differences in nutrient requirements among trees may help explain how so many species can coexist." Although plants in temperate forests influence the soils around them (through the uptake of nutrients, decomposition of leaf litter on the forest floor and through root exudates), in tropical forests local neighborhoods contain so many species that the ability of individual species to influence soil properties is likely to be small. "We interpret these plant-soil associations as directional responses of plants to variation in soil properties," the researchers wrote. The team also found that certain soil nutrients that previously had not been considered important to plant growth in tropical forests had measurable effects on species distributions. At the site in Ecuador, calcium and magnesium had the strongest effects. In the Panamanian forest, boron and potassium were the most influential nutrients assayed. And in the Colombian mountain forest, potassium, phosphorous, iron and nitrogen, in that order, showed the strongest effects on the distribution of trees. "There are all kinds of minerals out there that plants seem to be responding to that we didn't think were likely to be important," Dalling said. Further studies are needed, he said, to evaluate these influences in more detail. The other principal investigators on the study are Robert John, a post-doctoral researcher in the U. of I. department of plant biology; Kyle E. Harms, Louisiana State University; Joseph B. Yavitt, Cornell University; and Robert F. Stallard of the U.S. Geological Survey. Researchers on the study also are affiliated with Smithsonian Tropical Research Institute, Panama; the University of Georgia; Pontifical Catholic University of Ecuador; Instituto Alexander von Humboldt, Colombia; and the Field Museum of Natural History, Chicago. Related Links University of Illinois at Urbana-Champaign All About The Forests of Planet Earth Forestry News - Global and Local News, Science and Application
Health Of Brazilian Rainforest Depends On Dust From One Valley In Africa
Washington DC (SPX) Jan 04, 2007More than half of the dust needed for fertilizing the Brazilian rainforest is supplied by a valley in northern Chad, according to an international research team headed by Dr. Ilan Koren of the Institute's Environmental Sciences and Energy Research Department. In a study published recently in Environmental Research Letters, the scientists have explained how the Bodele valley's unique features might be responsible for making it such a major dust provider. |
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