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Restoration of degraded forest land in Thailand:
the case of Khao Kho

T. Marghescu

T. Marghescu is former Chief
Technical Adviser of FAO project
THA/88/017, "Reforestation of
Denuded Forest Lands in Khao

Lessons from an FAO project to reforest Thai highlands denuded through military action, influx of migrants and overexploitation for unsustainable agriculture.

Kao Kho, a district of Petchabun Province, is situated 400 km north of Bangkok in the middle of Thailand's central highlands. It is the southern tip of a mountain range (elevation 400 to almost 1 200 m above sea level) which stretches south from the Lao People's Democratic Republic into the Thai central plains. In the late 1960s, the district's area of roughly 130 000 ha was still mostly covered with dense forests (over 75 percent canopy), with dry dipterocarp forests on mostly poor soils in the lower parts and mixed deciduous and dry evergreen forests on generally fertile soils in the upper parts. Only small patches of open forest (25 to 75 percent canopy) were recorded, indicating shifting cultivation activities by the local hill tribes.

Ploughing of steep hillside for maize cultivation - with heavy erosion as a consequence


Barren landscape prepared for maize cultivation, with fruit trees in the foreground


An almost irreversible process of forest destruction and site degradation started in 1968, when the area became a stronghold for rebels attempting to overthrow the Royal Thai Government. Khao Kho was the site of 12 major battles between the rebels and the Royal Thai Army between 1968 and 1982. At the beginning of the 1970s, in a new strategy to end the insurgency, the Royal Thai Army began to build roads, to clear forests and to encourage local families to settle and to practise agriculture on assigned land, opening up the densely forested area.

Migrants from the lowlands began to pour into the area, clearing forests on mountain slopes for illegal maize cultivation, which was unsustainable on such steep terrain, and completely stripping the area of its forest cover. By 1990, the landscape was one of unprecedented erosion and site degradation. Forest covered only 10 percent of the land, scattered in patches over the area. The rest of the land was mostly used for unsustainable agriculture.

In 1990, the United Nations Development Programme (UNDP)-funded FAO project "Reforestation of Denuded Forest Lands in Khao Kho" was initiated, in cooperation with the Royal Thai Army and the Royal Thai Forest Department, to identify environmentally suitable land use options; to rehabilitate denuded forest lands through reforestation; to provide the setting for farmers to practise sustainable agriculture; and to create employment opportunities needed to avoid future deforestation. The project recruited both workers from local villages and illegal maize farmers from outside the area to participate in the reforestation activities.


The first plantation efforts demonstrated numerous problems. Most of the early plantations (91 percent) were established in rows downhill. This did not halt, but even accelerated, soil erosion. Since the government's immediate objective was to reforest the watershed, species were chosen primarily for fast growth, and the three species used - the non-indigenous Acacia mangium and Pinus carribea and the indigenous Pinus kesiya - were not economically useful to the local population. The plantations were often set on fire (sometimes accidentally, but often intentionally) by land-hungry poor families who regarded them as a competing land use. Moreover, the planting of monoculture blocks did not take into account micro-site conditions, and thus the growth and survival of planted trees was very uneven. Species diversity issues were not taken into consideration.

After the problems of the early plantations, the project management diversified the planting to take into account the socio-eonomic needs of the population, and concentrated on matching species to particular site conditions. Seven different site types were classified (according to soil moisture availability, degree of erosion, elevation and degree of human influence and human demand) so that appropriate species could be chosen that would optimize production; satisfy the economic and social demands of the local population; and improve, protect and preserve the environment (Table 1).

TABLE 1. Classification of site types and appropriate species

Site type

Species requirements

Species chosen


1  Roadsides and areas bordering agricultural fields and settlements: “social buffer” sites

Multipurpose tree species to benefit the local population and facilitate social acceptance of government plantations

- Azadirachta indica
- Cassia siamea
- Morus alba
- Sesbania grandiflora
- Cajanus cajan
- Leucaena leucocephala
- Mangifera caloneura


2  Erosion gullies and creeks on sloping land

Closely spaced deep-rooting pioneer species to provide permanent vegetation cover for soil conservation and erosion control (no intercropping or forest utilization)

- Thyrsostachys siamensis
- Bambusa arundinacea
- Bambusa blumeana
- Dendrocalamus strictus


3  Hilltops and ridges with shallower soils and minimal soil moisture, especially at the end of the dry season

Selection based on moisture requirements

- Eucalyptus camadulensis
- Pinus kesiya
- Pinus carribea
- Pterocarpus macrocarpus
- Betula alnoides
- Docynia indica
- Peltophorum dasyrachis
- Swietenia macrophylla
- Kylia kerrii


4  Middle slopes with moderate soil moisture availability during the dry season

Selection based on moisture requirements

- Acacia mangium
- Eucalyptus urophylla
- Ecualyptus deglupta
- Pterocarpus macrocarpus
- Xylia kerrii
- Lagerstroemia spp.
- Nauclea orientalis
- Mangifera caloneura


5  Slope feet with good soil moisture throughout year

Selection based on moisture requirements

- Choerospondias axillaris
- Dendrocalamus strictus
- Thyrsostachys siamensis
- Bambusa arundinacea
- Hopea odorata
- Dipterocarpus alatus
- Afzelia xylocarpa
- Chukrasia velutina


6  Valleys and creeks on flat land with natural streams, where soil moisture is maximal and floods occur frequently, especially through the rainy season

High moisture and flood tolerant species

- Azadirachta excelsa
- Dipterocarpus alatus
- Hopea odorata
- Bambusa arundinacea
- Eucalyptus deglupta


7  Areas below 450 m above sea level (maximum elevation for Tectona grandis)

Lower-altitude species

- Tectona grandis
- Afzelia xylocarpa
- Xylia kerrii
- Azadirachta indica


In matching the species to the site type certain principles were followed:

Remaining natural forest patches were surveyed to prepare a list of local indigenous species and their natural occurrence according to the site type classification. As a result of this survey, the tree species Choerospondias axillaris, for example, which had not been cultivated before, was identified and propagated with success. This species is now widely used for reforestation in the central highlands of Thailand. Altogether, more than 30 species were matched to the seven different site types, thus assisting the development of biodiversity.

To avoid the erosion problems caused by downhill planting (which became apparent during the 1991 rainy season), contour planting was introduced. For laying out the contour lines and marking the exact spacing of trees, the project adopted a wooden A-frame - a simple, inexpensive, foldable instrument shaped like the letter "A". The position of a weighted string suspended from the apex of the A-frame is marked on the horizontal bar of the A, and the A-frame is then rotated on one axis and manipulated until the string again falls in line with the mark on the bar. At that point, the two sides of the A-frame stand on the contour line, which is marked. The frame is then rotated another 180° and the procedure is repeated. The A-frames were produced by the project's carpenters and required a minimum of instruction. The weighted string was later replaced by an aluminium water level, which improved the acceptance of the instrument. All workers were trained in the use of the instrument, and from then on all plantations were established along contour lines.


When the reforestation project began in 1990, the illegal maize farmers, poor landless people from outside the area, violently opposed and even sabotaged it. The project officers reached a compromise with them, and agreed to opt for wide spacing, 2 m x 6 m, so that farmers could continue to plant maize between the tree lines for at least two more years, until the closing of the tree canopy would block the light needed by the crops. This was of course a temporary solution. For the longer term, the project reduced illegal farming on designated forest land by providing 150 landless families the opportunity to settle in three new villages where each family was allotted 2.4 ha for agriculture and 0.8 ha for a homestead. The project also provided the farmers with training (in agriculture, horticulture, livestock farming, aquaculture, community forestry, kitchen gardening, cottage industry development, health) to enable them to engage in sustainable farming on their allotted land.

By attending to the needs of the people in the area, providing opportunities for land use and employment and improving security, the project helped reduce pressure on degraded lands. Outbreak of fires and illegal land use dropped noticeably. Natural regeneration and succession flora began to thrive, especially near remnant patches of natural forest. The Khao Kho experience showed that when the pressures are lifted, degraded forest land can rehabilitate itself naturally and with much higher biological diversity than could be reached in any tree plantation. In view of this, the project management recommended to decision-makers that traditional reforestation could be reduced and the funds thus freed could be used to strengthen extension and fire protection (Marghescu, 1996).

Training in the use of the A-frame for contour marking




The development that was already beginning to be visible towards the end of FAO assistance to the area in 1995 has taken hold and continues to have positive effects on Khao Kho. The area today is known for its beautiful forest scenery and cool climate. A search for "Khao Kho" on the Internet leads to several sites advertising Khao Kho as the "Switzerland of Thailand". The rehabilitated forests have become an asset for tourism, bringing further benefits to the local population. 

Contour reforestation



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