Most tropical timber exports in recent decades have come from the timber-rich dipterocarp forests of Indonesia and Malaysia. The policies designed to ensure that timber harvesting from those forests can be sustained focus on getting loggers to just harvest trees larger than certain minimum diameters and to leave logged-over forests for 30-35 years before logging them again. They also encourage companies to plant trees and to clear the vegetation under existing trees to help them grow.

Despite these rules, logging in these countries has proven unsustainable and the forests are being rapidly destroyed. That is partly because logging companies break the laws and farmers clear forests to grow crops. To make things worse, scientists now say the existing rules are too weak to sustain timber harvests and some are misguided.

According to "Towards Sustainable Management of Mixed Dipterocarp Forests of Southeast Asia: Moving Beyond Minimum Diameter Cutting Limits", published by P. Sist, R. Fimbel, D. Sheil, R. Nasi, and M.H. Chevallier in Environmental Conservation, even if the companies did follow the existing laws logging would not be sustainble. Based on extensive experimental data, they conclude that companies have to harvest fewer trees and leave the forests for longer periods before logging them again. In addition, they have to completely stop cutting the rarer species and the largest trees, and avoid clearing large areas. They must also adopt reduced impact logging practices to avoid damaging the remaining trees, the habitats, and the soils. Otherwise, timber harvesting in these forests cannot be sustained.

The authors say companies should stop clearing the understory vegetation after logging , which can destroy the habitat of the insects that pollinate the trees. More generally, forestry prescriptions need to pay more attention to the conditions that trees need to reproduce, survive in their early stages of growth, and maintain genetic diversity, and the role that animals play in those processes.

The study’s implications are sobering. Governments have huge problems enforcing existing laws. Now it turns out that even if they succeeded it would not be enough. It is not clear what would happen to the companies’ profits if they followed the authors’ recommendations. What is clear is that the old way of doing things simply cannot continue.