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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
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