Giant Dipterocarp tree in Gunung Leuser National Park, Sumatra. My guide called this individual a ‘BMW tree,’ in that if logged it would generate enough cash to buy luxury car in Medan, Sumatra.
In recognition of the progress made on REDD — a scheme to protect rainforests — at climate talks in Copenhagen, this is a profile of a critical family of rainforest tree: Dipterocarpaceae.
Dipterocarps are the dominant family of canopy trees in Southeast Asia, but nowhere is their ecological role more pronounced than in Borneo.
Seed production in this family is inextricably linked to the arrival of El Nino. Dipoterocarps synchronize their reproduction, called masting, to the onset of the El Nino Southern Oscillation, which occurs approximately once every four years. The traditional climatic conditions of an El Nino year stimulate synchronous fruiting and subsequent flowering in the dipterocarps and are imperative for regional seed production, and ultimately, forest regeneration. Individual trees may carry up to 120 fruits and the trees have been known to synchronize over a scale of 370 million acres.
During a “dipterocarp year” in Kalimantan, the canopy bursts into color as countless emergent dipterocarp trees flower almost simultaneously. These mast flowerings, while correlated to El Nino, still occur somewhat randomly. This may be a strategy to intermittently starve and swamp seed predators so that at least some seeds survive to germination. The principle pollinators of dipterocarps are small insects called thirps, which have adapted short life cycles to coincide with the irregular masting periods. Between instances of flowering, small thirp populations feed on understory flowers for subsistence and when a mass flowering is triggered, the pollinating populations increase exponentially to take advantage of the vast number of blooms–around four million per tree.
Typically, natural seed production is so immense that there is a surplus for local fauna to gorge upon and local people to collect and sell. Lisa Curran (now of Stanford University, but formerly of Yale) has found significant changes in animal migration patterns and increases in populations during masting periods as animals come to feed. The trees produce so many seeds that the forest floor is literally carpeted during a five week period when a staggering 96 percent of the seeds may fall to the ground. With such a dense layering of seed it would seem there would be more than enough opportunity for some seelings to ascend to the canopy. However, with the present state of affairs in Kalimantan, this apparent excess of seeds is proving to be not nearly sufficient.
What has changed in the dipterocarp forests as a result of indiscriminate and heavy logging is the quantity of life-bearing seeds. Intensive logging in Kalimantan near the Gunung Palung National Park over the past two decades has taken a major toll on this reproductive cycle. In 1991, seed production was around 175 pounds per acre. By 1998, this number had plummeted to 16.5 pounds per acre, even though it was a major El Nino year. According to research gleaned by scientists, logging appears to reduce local density and biomass of mature trees and also limits the spatial extent of masting and inhibits the forest’s normal response by disrupting soil conditions. Extended drought stress is another effect of the felling. The reduction of seed results in a loss for the forest, the animals and the people.
The disappearance of the dipterocarp forests of Borneo would be more than a simple environmental loss; it would cause significant damage to Kalimantan economy which relies heavily on the timber industry that produces approximately $9.2 billion annually. Western Kalimantan is the third largest exporting region in Indonesia which controls 95 percent of the world’s tropical plywood trade and provides 80 percent of the plywood used in the United States. Currently more tropical timber is extracted from Borneo than all of Latin America and Africa combined. The success of the timber industry In Kalimantan is threatening its own survival by destroying this delicately functioning and interconnected ecosystem.
Most of this text about dipterocarps was written by Tina Butler in 2005. It had been edited by me