The Peat Forests of Sarawak

In 1961, Rob Anderson completed his doctoral degree at the University of Edinburgh after documenting the ecology and forest types across Sarawak (Rajang Delta) and Brunei (Baram Delta). At the time, peat-accumulating forests covered 5660 square miles (~14,700 km2) of this part of Borneo to a thickness, in peat domes, of more than 50 feet (16 m). Peat began accumulating no more than 7400 years ago (Staub and Gastaldo, 2003). Anderson had spent more than 1o intermittent years undertaking his project on behalf of the Forestry and Agricultural commission. Until 1949 there had been no previous scientific study or inventories of these forests. Following WWII, Malaysia began exploiting the forest resources to help drive the country’s economy. Anderson reports that the average yearly tonnage of wood products exported between 1948—1951 was 35,800 Hoppus round tons (=64,500 cubic m), after which logging nearly increased by 100% from 1952—1959. Over these 8 years, Sarawak exported an average of 282,300 Hoppus round tons (=508,400 cubic m) per year. Since then, deforestation continues until the present. Peak exports occurred in 2013 with 1,923,265 Hoppus round tons (3,052,460 cubic m) and has declined. In 2019, for example, 715,600 Hoppus round tons (=1.29 million cubic m) were exported (

Peat forests of southeast Asia are modern analogs for thick, economic coal deposits ranging in age from the late Mississippian (320 Ma) until the Miocene (30 Ma). The plant groups of the trees that contributed to these organic accumulations have evolved, dramatically, over time. Carboniferous peat forests were ecologically different wherein spore-bearing plants (horsetails, club mosses, ferns) dominated and seed plants (gymnosperms) were subdominant. Permian, Triassic, Jurassic and Cretaceous  forests were covered with seed-bearing (gymnosperm) trees. It wasn’t until the late Tertiary that angiosperm (flowering plants) trees out-competed  gymnosperms in these wetlands, and continue to comprise the peat-accumulating vegetation of today’s mires. The dominant plant group of the forests of Sarawak, Kalimantan, Sumatra, Java, Malaysia, and other parts of SouthEast Asia is the Dipterocarpaceae (classified in the Mallow or Hibiscus Order). Currently, there are 17 genera and 680 species (!) placed in this family of hardwood timber (ebony, mahogany, meranti, camphor). Mature trees grew to heights greater than 190 feet (65m) although there are reports of mature emergent canopy trees attaining 240 ft (73 m). One feature of the family is the presence of a buttressed rooting system, seen in this Shorea albida tree in Kuching (note Dr. Kate Bartram for scale). Few, if any, of these giants remain standing in the coastal lowland forests.

Anderson identified six ecological (phasic) communities in these swamp forests, with the largest and most robust trees growing adjacent to the rivers where occasional flooding deposited nutrient-rich sediment. Where saltwater incurred along rivers and tidal channels, and along the coastal zone, salt-tolerant plants grow. These include a suite of seven different mangroves which can grow to heights of 30—40 ft (9-12 m; black mangrove Avicennia; red mangrove Rhizophora).  Shorea albida (meranti) communities predominate these forests where the same species grow to several meters in diameters in width near the margins, grow to a width of tens of centimeters further inland (pole forests), and only a few centimeters at the top of domes. With increasingly thick peat soils from the margin to the interior of the forest, the diversity of trees and their diminished size is because of a decrease in available nutrients for growth. These forests are termed “raised mires” and are maintained by rainfall and the recycling of decaying plant matter of previous generations.

Sarawak’s peat forests have undergone dramatic deforestation over the past 30 years with several thousand square kilometers of forest logged, drained, and replanted in palm oil: Elaeis guineensis. As a result, the coastal skyline also has dramatically changed, even from when the image, below, was taken in 1993. At the time of this picture, I remarked to Mr. Haji Rosli bin Sahari, a forester with the Sarawak Department of Agriculture and indispensable colleague in the field, that the forest canopy structure was a memorable and impressive site against the setting sun. Haji remarked that I was not seeing the true forest canopy. Rather, the emergent trees actually represented what was left of the subcanopy. ALL of the large and impressive canopy trees already had been cut, logged, and exported. Even now, the skyline pictured, here, is just a fading memory never to return unless the peatlands are restored to their original ecology.

Rob Anderson’s seminal dissertation is available as a .pdf scan from the University of Edinburgh’s digital library.