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Forests and Other Ecosystems

El Niño can have major effects on forests and other ecosystems, as seen from recent experience and from paleoenvironmental data, including analyses of pollen, coral, and tree ring records around the world. For example, tree ring records in the U.S. Southwest show the correlation of the width of tree rings with precipitation and with the dry and wet years associated with El Niño. The dates of fires can also be reconstructed through tree ring analyses. In the U.S. Southwest, forest fires often occur when wet winters associated with El Niño and the buildup of vegetation are followed by dry periods associated with La Niña (Swetnam and Betancourt, 1990, 1992).

The 1982-1983 and 1997-1998 El Niño events clearly showed the effects of climatic variations on forest conditions in Austral-Asia and Latin America. In 1982-1983, more than 400,000 hectares of forest burned in East Kalimantan, Indonesia, and wildfires also devastated parts of Australia and southern Brazil. In 1997-1998, fires destroyed forests in Indonesia, the Philippines, Mexico, and Brazil. The World Wildlife Fund estimated the area burned in Indonesia at 6 million hectares, and in Brazil, about 5 million hectares of forest burned in the state of Roraima.

In addition to the obvious damage to the forestry industries of these regions, the impacts on biodiversity are serious. In Indonesia, the fires threatened several species, including endangered orangutans. In Mexico, the Chimalapas nature reserve, one of the regions with the highest biodiversity in North America, was severely damaged by fires in 1998. Costa Rica is concerned about the long-term effects of drought on biodiversity and ecotourism. Although natural vegetation is often adapted to climatic variability (Nicholls et al., 1991), human activity has sometimes increased the vulnerability of biodiversity to drought-induced fires. Policies of fire suppression to protect timber resources, homes, and tourist sites have led to the buildup of fuel and to more serious fires in the long run.

Agricultural encroachment on forests, especially through clearing by burning, has significantly increased the risk of forest fires. Forest managers have attempted to respond to climate variability by trying to obtain a better understanding of natural fire history and using historical knowledge and climate predictions to decide when to reduce fuel buildup through controlled burns. Governments have attempted to impose fire bans, including laws against the traditional slash-and-burn clearing of agricultural lands, and have invested extra resources in their firefighting services in dry years.

Marine ecosystems are heavily influenced by climatic variability, as noted in the discussion of fisheries above. Many of the species that feed on fish fluctuate with fish and marine phytoplankton populations in an El

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