Map of Cambodia showing Prey Lang Forest in boxed shaded area.

General Ecology
By David Ashwell, M.Sc.

The term Prey Lang has been used to refer to the extensive evergreen and semi-evergreen forest landscape that is located between the Mekong and Stung Sen Rivers in northern Cambodia. It is centered upon the remnants of the original surface of the ancient alluvial plain that once extended across northern Cambodia but much of which has long been eroded away. Smaller areas of similar sediments are located in Beong Pe Wildlife Sanctuary in Rovieng and other contiguous districts. This area supports roughly 3,600 square kilometers of forests. It measures roughly 120 km in its north-south axis from Kampong Cham province to the Laos border, and 30km in its east west axis from the Mekong River to the Stung Sen River.

Lowland dry evergreen forests dominate the central portions of the alluvial plain and are associated with the red-yellow podzol soils. The forest grades through lowland semi-evergreen forest upon the grey hydromorphic soils to deciduous forests in more peripheral areas where they are associated with the less productive plinthite podzols and/or shallow lithosols soils.

In addition to the dry evergreen, semi-evergreen and deciduous forests this landscape also features a number of other forest communities. They include mixed deciduous forests dominated by Lagestroemia, short riparian and Melaleuca forests, short semi-evergreen forests, deciduous swamp forests and evergreen swamp forests.

Siamese Crocodile

Biodiversity Values

This heavily forested landscape has particularly high conservation values. The areas have a particularly high potential for the conservation and sustainable use of biodiversity. These values stem from:
• It being the largest primary lowland dry evergreen forest remaining in both Cambodia and Indochinese Peninsula.
• The existence of the range of critical and fragile habitats including swamp forests that may acts as repositories of ancient forest lineages and species with narrow ecological tolerances.
• The existence of healthy wildlife populations including endangered species such as elephants, gaur, banteng, tiger and Asiatic black bears.

All of the forest types described here warrant some form of protection. This is particularly true for the lowland dry evergreen forests and the evergreen swamp forests. These forests are rich in biodiversity and rare species. Both of these forest types are quintessentially Cambodian in origin and character. The evergreen swamp forests appear to constitute a forest formation that is endemic to Cambodia.

The lowland dry evergreen forests are distinctive from those on other lowland forests associated with the Cardamom and Elephant Ranges in the south-west, and the southern Annamites in the north east. It is also apparent that these forests maintain a level of biodiversity that equals or exceeds other lowland areas in Cambodia. The biological value of Prey Lang seems all the more critical because most the Cambodia’s protected evergreen forests are located in or near mountainous regions (MacDonald 2004). These tall dipterocarp forests of central Cambodia are of global significance, in that they represent a type of vegetation that was once formerly common throughout the whole of South East Asia but has largely been extirpated from the region.

Dry evergreen forests on alluvial soils, especially those communities on the alluvial soils, have been subject to extensive logging during the last decade and remain particularly vulnerable to future logging. As a result of the extensive nature of these impacts only the core area of the Prey Lang forest located within the upper catchments of the Stung Porong and O Long watercourses may be considered to be primary lowland dry evergreen forest (MacDonald 2005). Indeed, this forest now remains the largest patch of primary evergreen forest within both Cambodia, and the entire Indochinese floristic province. This area lies within the unlogged portions of Colexim and Everbright concessions and was also untouched by logging operations in the 1960s.

The inclusion of roughly 80,000 to 100,000 hectares of unlogged or primary stands of this forest type places particular importance upon this focal area because this forest type has suffered heavy levels of deforestation and degradation throughout its range in the Indo-Chinese floristic province.

These forests are habitat to wide diversity of Cambodia’s vascular plants including 11 threatened tree species and 19 of the 21 species prioritized for genetic conservation by the CTSP; as well as a diverse array of timber species. In addition, the area retains a range of key wildlife species including elephant, gaur, banteng, gibbons and hornbills. Although survey effort in this area is very limited it is already apparent that Prey Lang features 16 to 22 threatened mammals, seven to 21 threatened birds and three to seven threatened reptiles.

A Sambar

Ecosystem Services

This forest landscape has particularly high social values. These derive from:
• The large population living either within or peripheral to this landscape.
• Its historical and current role as a provided of non-timber forest products to a large portion of the Cambodian population on a daily basis.

Villages are generally located along the larger streams and therefore around the periphery of the Prey Lang Forest although some recent settlement has targeted areas that were relatively remote until recent years. Over 250,000 people live in 339 villages that are largely located within the peripheral areas of this landscape. This landscape has a particular importance as it provides a livelihood for some ethnic minorities, notably the Kouy. A further 450,000 people live in 450 villages within ten kilometers of the boundary of this landscape.

While this area has been a focus for commercial timber extraction in its recent history its principal utilitarian values appear to lie elsewhere. It has important watershed values. It is apparent that these forests have a broader significance in the water cycle within northern Cambodia as they play a critical role in provoking rains in central Cambodia and in maintaining water in the region throughout the year. Its extensive catchment area and deep soils constitute an important contribution to the maintenance of dry season flows. The role that both the dry evergreen and swamp evergreen forests play in regulating water flows also serves to prevent sedimentation of the Tonle Sap Lake.

These waters drain either directly to the Mekong or Stung Sen rivers, or to the Tonlé Sap Lake via the Stung Chinit River. Thus, Prey Lang contributes substantial waters to the agricultural areas on the floodplain of the Stung Sen River as well as those further downstream. The Stung Chinit River is also of particular importance because it directly supplies downstream agricultural areas in Kampong Thom that are the focus of development efforts.

Prey Lang also has important roles in the provision of non timber forest products. It is a major source of tree resin within Cambodia. This resin is tapped in traditional manner from the large dipterocarp trees and sold to traders who sell in the domestic or export markets. Much of the resin is directly exported to Vietnam. The semi-evergreen forests are an important and traditional source of commercial bamboo harvests.

Perhaps the least well understood ecosystem service provided by Prey Lang is that of carbon sequestration. The lowland evergreen forests appear to store more carbon that any other forest type in the country as they have perhaps the highest timber volumes and biomass of Cambodia’s forests when in an undisturbed state. They are therefore of particular importance to the consideration of Cambodia’s GHG emissions. The fact that much of the forest within this landscape has undergone heavy degradation adds additional importance to forest regeneration. If these degraded forest areas are allowed to regenerate this will result in the sequestration of very substantial amounts of carbon.

Degradation and Threats

Forest areas within this focal area have been substantially degraded by logging since 1993. This degradation was largely associated with timber mining within a number of logging concessions including Colexim, Everbright, GAT, Mieng Ly Heng, Pheapimex and Timas. As a result of these activities there is an extensive network of logging roads within the east, north and south of the Prey Lang landscape. Much of the Mieng Ly Heng concession area has been cleared. Currently, it is estimated that 80,000 to 100,000 hectares remain in a pristine state.

The center of Prey Lang lies within the Everbright and Colexim logging concessions, which were two of the concessions the World Bank did not recommend for cancellation. These concessions remain on paper though there is no sign that they will begin operations in the near future. GAT and Mieng Ly Heng concessions (in Kompong Thom and Preah Vihear) were cancelled, but the Pheapimex concessions remain on paper (though they were recommended for cancellation).

Substantial land clearance and logging is still continuing, particularly in the western area towards the Stung Sen River and virtually the entire extent of the former Mieng Ly Heng logging concession is reportedly been given out to economic land concessions as have some areas to the northwest of Kratie township. In addition, areas of productive red soils near Tumring have been converted for rubber production. This degradation of the forest resources by both legal and illegal logging operations in recent years has been exacerbated by in-migration of people associated with agricultural developments, charcoal production and gold mining.

Economic land concessions: The Tumring rubber plantation in Sandan district was made by clearing an area of forests and chamkars near the periphery of Prey Lang. Other economic land concessions are being developed nearby. Further north (in Kompong Thom and Preah Vihear) and in Kratie, companies have discussed plans for development of plantations with local authorities but their status isn’t clear. Apparently no operations have begun on the ground. Given trends in Cambodia, it is likely that there will be extreme pressure to grant large areas of Prey Lang as economic land concessions.

Logging: There is logging around Prey Lang but little logging within the core zone. Most of the logging around Prey Lang is of luxury species, except in the southern part where various timbers are taken. There are also isolated cases of cutting of koki and duong chem trees. Several koki trees have been taken out of the middle of Prey Lang in recent years, ostensibly to make racing boats. Roads were cleared into the forest to take out individual trees. A military unit at Romuol on the Mekong River is reportedly involved in much of the logging. Much of the former Mieng Ly Heng timber concession has been deforested in recent years.

Monkey trade: Around the periphery of Prey Lang people catch monkeys to sell; they apparently end up in government-licensed monkey farms around Prey Lang. To catch monkeys, people clear an area of forest as large as one hectare, so these operations deplete the monkey populations and also destroy the forest.

Mining: People have mined gold at Phnom Chi in the southern part of the Prey Lang area for years. There have been problems of poisoning the Stung Chinit River below Prey Lang. Now a concession has been granted to a foreign company for a gold mine there. Other mining leases are active in Thala Borivat (Figure 26). Several companies are investigating possibilities of starting mining operations in the Prey Lang area in Sambor district. In Preah Vihear and Stung Treng, iron mining operations are beginning outside (but near) the Prey Lang area. In the future, mining concessions are likely to constitute a major threat to Prey Lang, particularly in Rovieng district which is known to have a diversity of mineral deposits (Workman and Fontaine 1978). An iron mine was active at Phnom Dek in Rovieng prior to the war. There are anecdotal reports that this was the site of artisanal mining by the Kouy for centuries.

Dams: Proposals have being made for damming the mainstream Mekong River at Sambor though the master plan upon hydropower development prepared with the support of JICA omits them from consideration. The construction of a mainstream dam would impact on the Mekong River system but is also likely to impact on Prey Lang. The demography of the local area would change dramatically and access to Prey Lang opened up. Currently, the only access from Kratie is by crossing the Mekong by boat. Dam construction on the mainstream Mekong at Don Sahong (in Laos, on the Cambodian border) will have huge environmental impacts; it will destroy deep-water pools used by fish breed stock, block fish migration, and likely lead to a collapse of fish stocks in the Tonle Sap.

A large dam could be established on the Stung Sen River between Prey Lang and Boeng Pe Wildlife Sanctuary though this is not indicated as a priority in the master planning for hydroelectric development. If established this would flood an extensive area within northern Cambodia and require a significant amount of relocation of villages. Much of the projected dam area overlaps with the diversity of mineral deposits in Rovieng District.

Social concessions and immigration: Families from Kompong Cham province have been relocated in Sandan at the periphery of the Prey Lang area through agreement between the governors of Kompong Cham and Kompong Thom provinces. Social concessions are also rumored to be planned for the periphery of the Prey Lang area in Stung Treng. Migration into the Prey Lang area has been facilitated by roads built by the logging companies, and is most significant in Sandan district. People in most of the local communities are moving further into the forest, and people from other provinces are moving into the periphery of Prey Lang in Sandan district.

Roads: The logging companies (Mieng Ly Heng, Colexim, Pheapimex, Everbright) built roads into Prey Lang and these roads have facilitated migration into Prey Lang as mentioned above. There are numerous smaller roads accessible by truck into the middle of Prey Lang, used for transporting resin, and there are smaller tracks through much of Prey Lang used by resin tappers. There are rumors of plans to construct a road across Prey Lang, from east to west, to connect Sandan and Sambor districts. This could partition Prey Lang and would likely lead to the irreversible destruction of Prey Lang.

Wildlife trade: There is a significant trade in wildlife from Prey Lang, with most wildlife leaving through Sandan district. The military base at Romuol (in Sambor district) is another important center of the wildlife trade. Buyers on motorbike travel throughout Prey Lang, visiting resin camps. Species targeted are primarily smaller species such as turtles, monitor lizards, etc.
Agriculture: There are several chamkars in the middle of Prey Lang, along the Stung Po Rong and Stung Damrei. They have expanded in recent years. Encroachment of farms is also associated with migration as described above.

Use of vehicles: Motorbikes are used by resin tappers, particularly those coming from Sandan. Trucks are used to transport resin, and go as far as the middle of Prey Lang. As other threats are dealt with, the use of vehicles will have to be dealt with in order to allow wildlife to recover.

Excerpt from: Ashwell, D. A. (2008) Biodiversity Profile for the Biodiversity and Grassroots Advocacy Project. USAID/EWMI-PRAJ, East West Management Institute, Phnom Penh, Cambodia

Disclaimer: This report is made possible by the generous support of the American people through the United States Agency for International Development (USAID). The contents are the responsibility of EWMI and do not necessarily reflect the views of USAID or the United States Government.