El Niño triggers tropical forest reproduction

December 07, 1999

El Nino triggers Indonesian tropical forest reproduction, says U-M scientist. Logging is destroying forest ecosystem, threatens local economy and global exports.

ANN ARBOR---On the island of Borneo, the world's second largest tropical rain forest is dying.

Its death will mean the disappearance of a unique ecosystem where trees time their reproduction to match the periodic arrival of El Nino. Loss of the forest also could have a global financial impact, since timber exports contribute as much as $8 billion annually to the Indonesian economy and provide 80 percent of plywood used in the U.S. home construction industry.

According to a study published in the Dec. 10 issue of Science by an international research team led by U-M tropical ecologist Lisa M. Curran, this ecological and economic resource is being destroyed by human activity, which has intensified the effects of regional climate change.

From 1985 to 1999, Curran and her colleagues studied Dipterocarpaca---the main family of rain forest canopy trees in Indonesian Borneo. Field research covered a 57-square-mile area, but focused on six square miles in the Gunung Palung National Park. The research team also surveyed timber concessions throughout the surrounding province of West Kalimantan and studied 30 years of export records to determine the impact of logging in the region and on the park.

Curran's study is the first to document an ecosystem with a rare reproductive strategy called masting. More than 50 different species of Bornean dipterocarp trees synchronize their reproduction---limiting fruit and seed production to brief, intense periods. Curran discovered that these bursts of reproduction are initiated by the arrival of the El Nino Southern Oscillation or ENSO, a periodic shift in tropical Pacific circulation patterns that brings drought to Indonesia.

"We recorded four masting episodes from 1986 to 1999 with an average interval of 3.7 years," said Curran, an assistant professor of tropical ecology at the U-M. "With the possible exception of one very minor event in 1994, they all occurred during ENSO years. Climatic conditions of an El Nino year trigger simultaneous fruiting in dipterocarps, and are essential for regional seed production."

According to Curran, masting gives canopy trees an important survival advantage. In a typical six-week masting period, her research team collected 180 pounds of seed---ranging in size from a chestnut to a pistachio nut---from every acre of the six-square-mile survey area on the forest floor.

"It's like Thanksgiving in the forest," Curran said. Wild boar, orangutans, parakeets, jungle fowl, partridges, and other animals congregate to stuff themselves. Local villagers collect baskets of seeds called illipe nuts to sell as a cash crop. Because so much seed is produced simultaneously over such a large area, however, there is still enough leftover to germinate and produce a carpet of new seedlings on the forest floor.

In the Science article, Curran and her co-researchers describe how the forest in Gunung Palung is changing following a decade of intensive dipterocarp logging in huge timber concessions surrounding the park. From 1991 to 1998, production of mature, viable dipterocarp seed fell from 175 pounds per acre (196 kilograms per hectare) to 16.5 pounds per acre (18.5 kilograms per hectare). Despite a major fruiting event during the 1998 El Nino year, no new dipterocarp seedlings were found in the survey area.

"Even though the park is supposedly off-limits to logging, the forest is losing the ability to regenerate itself," Curran said. Because seed predators can't find food outside the park, they move inside to eat the dipterocarp seeds before they germinate, according to Curran. Massive forest fires on nearby logging plantations, which destroyed an area the size or Denmark or Costa Rica in 1997-98, brought pollution and intensified El Nino's drought killing the few remaining dipterocarp seedlings.

"It's very sad, but unless the Indonesian government implements sustainable forestry practices, creates financial incentives to harvest responsibly, and prevents clearing and burning for industrial plantations, this ecosystem will be unable to recover," Curran said. "The real injustice here is to the Indonesian people in Kalimantan, because the majority depend on the forest for their basic livelihood. They will bear the environmental and socioeconomic costs, but the benefits from this harvest went to a few timber tycoons."

The research was supported by the U.S. Agency for International Development, National Science Foundation, U-M, International Timber Trade Organization, Wildlife Conservation Society, World Wide Fund for Nature, Conservation International, W. Alton Jones Foundation, National Geographic Society, and the Conservation, Food and Health Foundation.

Collaborators in the research study include Gary Paoli, U-M graduate student; Izefri Caniago, from the U.S. Agency for International Development in West Kalimantan; Dwi Astianti, from the University of Tanjungpura in West Kalimantan; Monika Kusneti, from the World Wide Fund for Nature; Mark Leighton of Harvard University; C. Endah Nirarita, from Wetlands International in Indonesia; and Herman Haeruman from the Indonesian National Development Planning Agency.
EDITORS: Color slides of Gunung Palung National Park are available on request.

The University of Michigan
News Service
412 Maynard
Ann Arbor, MI 48109-1399

University of Michigan

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