DURHAM, N.C. -- The delicate ecological web of the tropical rain forest is permanently unraveled by heavy logging, according to the most comprehensive long-term study yet done of the effects of timber-cutting on a rain forest.
The researcher, Duke University biologist Thomas Struhsaker, concludes that even so-called "sustainable" harvesting practices used in some countries are far too intensive to protect rain forest ecology. He advocates that rain forest preserves be spared completely from logging. And, for rain forests that are to be logged sustainably, harvesting must mimic natural treefalls -- consisting of no more than one large tree per hectare per century, done by hand to minimize forest disruption.
The findings describe the results of 23 years of studying the 560-square-kilometer (216-square-mile) Kibale rain forest in Uganda. The study represents the first time the interrelations of both plants and animals have been incorporated into a long-term study of logging, said Struhsaker.
"This is a study that really looks at the impact of logging on the wildlife," he said. "Most of the others have looked primarily at commercial timber species, not even considering the rest of the flora."
Such breadth was particularly important in understanding rain forest ecology, Struhsaker said, because in tropical rain forests, animals are more important to the perpetuation of the trees and plants than in temperate forests.
"In temperate regions many plants are pollinated by and have their seeds dispersed by wind," he said, "whereas in tropical forests a much higher proportion of these tasks are done by animals."
Understanding the full complexities of the tropical rain forests also is critical given the importance of the tropical rain forests in the planet's ecology, Struhsaker said. Although tropical rain forests cover less than 10 percent of Earth's surface, they contain more than 50 percent of all species.
The findings by Struhsaker and his colleagues have just been published in a book Ecology of an African Rain Forest: Logging in Kibale and the Conflict between Conservation and Exploitation (University of Florida Press, Gainesville, Fla.).
"The great tragedy is that tropical rain forests are currently being lost more rapidly than ever before in the history of humankind," he wrote in his book.
"The destruction of these forests is indisputably one of the greatest ecological disasters in the history of Homo sapiens," he said. He cited estimates that an area of tropical rain forest the size of Greece or the state of Florida is being converted to agriculture each year.
The book also describes the impact of Uganda's severe political upheaval on the scientists' research and conservation activities. The civil wars -- in which hundreds of thousands of Ugandans were massacred -- also thrust Struhsaker and his fellow scientists into perilous encounters with soldiers and guerilla bands. And, the scientists' insistence on reporting poaching and official corruption in the national reserve led to death threats.
Struhsaker began his work in Kibale in 1970. At first, he and his colleagues studied the many species of monkeys and apes in the area. However, in 1976 the scientists expanded their work to include the effects of logging on animals and the forest ecosystem as a whole. Overall, some 28 scientists contributed to the research over its 23 years. Also, over the study's lifetime, the study expanded from a concentration on basic research to include studies of logging as well as lobbying and conservation efforts.
The Kibale research was funded by the National Science Foundation, National Institutes of Health, New York Zoological Society, African Wildlife Fund, World Wildlife Fund, National Geographic Society, U.S. Embassy and the East African Wildlife Society. The researchers' local sponsor was the Department of Zoology in Uganda's Makerere University. The study was also officially supported by the Ugandan Government Forest and Game Departments, the Ugandan National Research Council and the President's Office.
Some specific findings of the study:
- Heavy logging severely reduced the diversity of species in the logged areas. Even after decades, the forest -- including both the animals and the commercial timber species -- had not recovered significantly.
- Logged forests had more and larger gaps and greater density of thicket plants, which reduced the survival of tree seeds and seedlings.
- The monkey species in logged areas still had lower densities of social groups at least 18 years after logging. Such reduction in social groups likely reduced genetic fitness of the populations. Hunting of the primates was also made easier in the logged areas of West and Central Africa.
- Rodent populations increased considerably in logged areas, because of the increase in thicket growth. This population increase caused a reduced survival of tree seeds and seedlings, because the rodents fed on them, suppressing forest recovery.
- Elephants used heavily logged areas much more than lightly or unlogged forest, also damaging young trees and suppressing forest recovery.
These and other findings led Struhsaker to conclude that sustainable logging could only be done in a tropical rain forest if fellings were spaced far apart, were limited to large trees and were reduced to only about one mature tree per hectare per century. Also, harvesting should not be done with large-scale machinery, to minimize damage to the forest.
The Kibale study has also convinced Struhsaker that it is impractical to manage tropical forests to increase timber yield beyond that of a natural forest or even to restore damaged ecosystems -- while at the same time maintaining viable populations of plant and animal species found in old-growth forests, he said. For one thing, he said, such management is expensive and requires an investment in a project that may not yield returns for 75 to 100 years.
"Far more time, labor and money must be invested in post-logging management in order to achieve adequate forest regeneration than if the damage due to logging had been minimized," he wrote. In any case, such management is likely to fail, given the complexity of the forest ecosystem and the fact that loggers invariably push to maximize short-term profits.
In general, these systems are so complicated, and there's so much natural variation in them, that you cannot separate the impact of the harvest from the natural variation until often 20 years or more after the fact. In the meantime, you've likely made some wrong management decisions."
Similarly, he said, attempting to rehabilitate habitats is incredibly expensive and not likely to restore a complex ecosystem on a large scale.
Struhsaker's observations of rain forest logging worldwide lead him to believe that logging will accelerate, and with it the loss of tropical rain forest.
"As timber resources around the world become depleted, more and more species that are not considered valuable today will become valuable tomorrow, and will be logged, he said. What's more, he said, timber companies will move into new areas of untouched forest.
"Already, we know that the big timber companies in Indonesia and Malaysia are moving to South America. They've finished the resources in Southeast Asia and now they're moving on."
Struhsaker's experience has convinced him that the only long-term solution to conserve forests in developing countries is population control, energy conservation to reduce wood use and strong forest management policies by stable governments.
To achieve these ends, he advocates that U.S. foreign aid and international development funds be predicated on a recipient nation's commitment to achieve goals in these areas.
Struhsaker also emphasized that so-called developed nations -- the principal market for tropical woods -- must also do their part to reduce their own rates of consumption of natural resources.
### Note to editors: A color photograph of Thomas Struhsaker is available on <www.dukenews.duke.edu> or by calling Dennis Meredith. Audiotape is available on 1-800-442-DUKE. Struhsaker is available at (919) 490-5352 (home, call there first) or (919) 490-6286 (office).
Review copies of the book may be obtained from Meg Varley, (352) 392-1351; E-mail: email@example.com