Borneo’s ecosystems are under siege. Massive deforestation is taking its toll on endangered species, endangered communities and our endangered planet.
The native forests of Borneo have been impacted by selective logging, fire, and conversion to plantations at unprecedented scales since industrial-scale extractive industries began in the early 1970s. There is no island-wide documentation of forest clearance or logging since the 1970s. This creates an information gap for conservation planning, especially with regard to selectively logged forests that maintain high conservation potential. Analyzing LANDSAT images, we estimate that 75.7% (558,060 km2) of Borneo’s area (737,188 km2) was forested around 1973. Based upon a forest cover map for 2010 derived using ALOS-PALSAR and visually reviewing LANDSAT images, we estimate that the 1973 forest area had declined by 168,493 km2 (30.2%) in 2010.
The highest losses were recorded in Sabah and Kalimantan with 39.5% and 30.7% of their total forest area in 1973 becoming non-forest in 2010, and the lowest in Brunei and Sarawak (8.4%, and 23.1%).
We mapped 271,819 km of primary logging roads that were created between 1973 and 2010. The greatest density of logging roads was found in Sarawak, at 0.89 km km−2, and the lowest density in Brunei, at 0.18 km km−2. Analyzing MODIS-based tree cover maps, we estimate that logging operated within 700 m of primary logging roads. Using this distance, we estimate that 266,257 km2 of 1973 forest cover has been logged. With 389,566 km2 (52.8%) of the island remaining forested, of which 209,649 km2 remains intact. There is still hope for biodiversity conservation in Borneo.
Conservationists have historically prioritized the protection of ‘pristine’, ‘old-growth’ tropical forests over human-modified ones. Pristine tropical forests are becoming increasingly rare, however, particularly in the lowlands of South-East Asia due to widespread timber extraction (“logging”), conversion to other land uses and increased vulnerability to fire. The conservation value of selectively-logged forests has been increasingly highlighted as requiring recognition. Selective timber extraction prevails in tropical forests meaning that only a few stems (typically 4–10) are removed from each hectare leaving a diverse forest still standing. These modified habitats retain appreciable biodiversity and serve as effective buffers and corridors for wildlife moving between intact forest fragments.
Borneo’s forests include old-growth lowland, hill and montane dipterocarp forests, freshwater and peat swamp forests, heath forests (kerangas), and mangrove forests (including areas dominated by the palm Nypa fruticans Wurmb locally termed nipah). These forests possess some of the richest biological communities on the planet and should therefore be preserved. But, much has already been logged − between 1980 and 2000 more round wood was harvested from Borneo than from Africa and the Amazon combined − or destroyed by fire, or converted to plantations.
Forest conversion encompasses clearing forest to establish industrial oil palm (Elaeis guineensis), and to a lesser extent acacia (Acacia spp) and rubber tree (Hevea brasiliensis) plantations. There is no island-wide satellite-based documentation of forest clearance, conversion or logging and the island remains under studied in this respect compared to other major tropical regions, although a recent study filled this gap for the northern part of Borneo.
Confusion reigns over the actual extent of deforestation, remaining intact and logged-over forests hampering proper conservation planning. For example, Indonesia’s pledge to maintain at least 45% of forest in the Indonesian part of Borneo (Kalimantan) was criticized by environmental groups reporting that Kalimantan retains only 30% forest cover, appreciably less than the 55% reported by Indonesia’s Ministry of Forestry.
Building on a detailed, LANDSAT-based, spatial inventory of forest cover, clearance and logging over the 1973–2010 period, the era of industrial-scale forest exploitation on the island, we address the following questions: (i) what was the extent of forest cover in the early 1970s; (ii) how much has been selectively logged or cleared since; and (iii) how are remaining intact and logged forests distributed across zones designated for protection, timber production, or conversion to plantations?
An estimated 389,566 km2 (52.8%) of the island remained forested (either intact or logged) in 2010. Intact forests represent 53.8% (209,649 km2) of the total remaining forest area or 28.4% of the whole Borneo. Brunei has the highest proportion of intact forest area at 56.9%, compared to 32.6% in Kalimantan, 19.1% in Sabah and 14.6% in Sarawak.
Much of the remaining intact forests will be logged and converted under the current forest-use designations. Some 42% (88,150 km2) of intact forests fall within the ‘production forest’ land-use class and will be logged. The actual area of intact forest in the land use designated for production is greater than the area of intact forests in protected areas. A further 16% (33,548 km2) of these intact forests will be converted based on their intended land-use.
Given the present distribution of intact forest across land use designations, the future extent of intact forest for all Borneo may decline to only 87,953 km2, or 11.9% of Borneo, assuming that all production forests are ultimately logged, area designated for conversion is ultimately converted or degraded, assuming protected intact forests remain unperturbed and that the extents of these land-use decisions remain unchanged.
For the lowland forests (<500 m asl), the most threatened, the corresponding figures are 33,773 km2 and 5.6% of Borneo’s lowlands. We observed an appreciable area of logged forest within the protection designation, which prohibits logging. Of the 179,917 km2 of current logged forest in Borneo, 10.3% falls within the protected areas wherein it constitutes 17% of all forest cover. Some, but not all, of this logged forest is evidence of illegal logging. In other cases, it evidences legally logged forests that were later re-designated for protection, e.g., the Sebangau National Park, declared in 2004.
While our data do not allow distinguishing illegal from legal logging per se, it is reasonable to assume that some logged forests within the protection designation were exploited illegally.