As human populations and their impacts on the world increase, tropical forests are changing in many different ways. Forests are being cleared, burned, logged, fragmented, and overhunted and an unprecedented pace, and they are also being altered in insidious ways by global climatic and atmospheric changes. "The evidence for global effects suggests that a massive reorganization of the structure and dynamics of tropical forests is already underway" writes ecologist S. Joseph Wright, "The tropics support over half of all species and over two-thirds of all people. Without an appropriate commitment from the scientific community, the two are unlikely to continue to coexist," concludes the scientist.
Tropical forest landscapes are changing rapidly in the eyes of scientists working on tropical monitoring plots around the globe, while human populations and their economic activities grow. Old-growth forests become agricultural lands, degraded land is abandoned, urbanization intensifies, and the populations of tropical countries will increase by two billion over the next 25 years.
But what is happening in protected areas? Globally, 18% of all tropical and subtropical moist forest and 9% of all tropical dry forests are nominally protected by governments. Increasingly, even these areas seem to be bearing the indelible marks of human activity.
On Barro Colorado Island (BCI) administered by the Smithsonian Tropical Research Institute (STRI) in the Republic of Panama, the old-growth forest has escaped fire and agriculture for at least 1500 years. STRI's Center for Tropical Forest Science (CTFS) has repeatedly censused all steams one centimeter of diameter or more at 1.3 m height in a 50-hectare plot every five years since 1985. Wright notes that the aboveground biomass on BCI was almost constant since the first census. But lianas increased substantially (from 9% to 13% of all leaf biomass) between 1986 and 2002.
In another protected area, the Kibale National Park in Uganda, a 30-year record suggests that reproductive activity by forest trees is increasing; and at La Selva, Costa Rica, diameter-growth rates decreased among surviving individuals for cohorts of nine species measured annually for 17 years. These mysterious changes may be caused by large-scale drivers, such as increasing carbon dioxide in the atmosphere, intense droughts, or other poorly understood phenomena.
Wright, who has studied tropical forests and its plant and animal inhabitants since the late '70 at STRI, encourages tropical scientists to conduct assessments based on existing long-term records. Basic research will help us to understand the dimensions and mechanisms of forest responses to anthropogenic forcing. Conservation scientists must help to mitigate the number of species lost to extinction by enhancing the effectiveness of the network of protected areas. Other applied research will help to rehabilitate degraded lands and to improve agricultural yields and living standards.
According to William F. Laurance, Wright's colleague at STRI and frequent spokesman for conservation efforts in Africa and the Amazon, "the commitment of tropical biologists must go a step further to include effective communication of their findings to decision makers and the general public. It is those who will eventually demand that governments invest in research and conservation of tropical forests and who will work to slow the rapid, unsustainable growth of human populations in the tropics."
Ref.: Wright, S. Joseph. 2005. "Tropical forests in a changing environment." Trends in Ecology & Evolution Online.
The Smithsonian Tropical Research Institute (STRI), with headquarters in Panama City, Panama, is one of the world's leading centers for basic research on the ecology, behavior and evolution of tropical organisms. http://www.stri.org
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