1 Land Cover Assessment of 1992/93

4.1.1 Classification Scheme

The following land cover categories were identified for the NOAA AVHRR classification. While selecting the classes, spectral separability of the sensor and user’s preference were given due consideration.

1. Forests : This includes evergreen and deciduous forests including mangrove forests. With the limited imageries available which are often covered with persistent cloud cover in much part of the Peninsula and north-west, it was not possible to classify evergreen and deciduous forests separately. However, secondary information can be used to segregate them. The distribution, elevation range and dominant species of major forest types found in Thailand has been presented in Table. 1.
2. Crop Lands : Crop lands are the cultivated areas along the plains, valleys and uplands. Crop lands generally include rice paddy, upland crops, horticulture, para rubber, oil palm and perennial crops etc.
3. Paddy Field: Irrigated rice paddy in the central plain is distinct in the AVHRR imagery. Due to its strong unique signature, it was possible to classify it as a separate class.
4. Waterbodies : Waterbodies are represented by reservoir, rivers and water depressions.
5. No Data Available : This class consists of areas covered by clouds and in some cases areas affected by topographic effects such as mountain shadow.

From the interpretation of 1992/93 AVHRR data, four major land cover types viz. forests, agriculture, paddy field (irrigated) and waterbodies were discerned. It was extremely difficult to discriminate evergreen and deciduous forests in the north as they occur in complex mosaic. In the south it is relatively easier, where large tracts of evergreen forests are abundant. To avoid confusion, particularly in the north, forest types were not subdivided, and are classified as ‘forests’. The ‘forests’ also includes mangrove vegetation.

From the analysis of multi-temporal/multi-seasonal NOAA AVHRR HRPT data it was found that the forests cover 30.17% of the total land area of Thailand. This includes both evergreen, deciduous and mangrove forests. Croplands are the dominant land cover type that covers more than 56% of the country. Including irrigated paddy rice, total coverage of the croplands accounts for more than 63%. The seasonal change of the signature of paddy rice which appeared in red color has been presented in the following figure.
 
 

Waterbodies cover less than 1% of the country including dams, rivers, water depressions and lakes etc. The distribution of land cover type and extent of Thailand are presented in Table 6.

Distribution of forests and population according to the region are presented in Table 7.

Table 7. Distribution of Population and Forests by Region
 

Fig. 5. Normalized Difference Vegetation Index Image of 31 January, 1993

Protected areas in Thailand are relatively well protected by law from encroachment, logging and collecting and hunting in the park. The law enforcement is, however, weak in some cases. Since the establishment of Thailand’s first national park in 1962, the growth of national parks has been increasing. Now there are 77 national parks and 36 wildlife sanctuaries (Ongsomwang, 1995). The distribution of these national parks and associated land cover types are presented in Map 2. It is noticed that some of the protected areas are encroached or affected by agricultural activities.

4.2 Land Cover Monitoring : 1985-1992

Land cover change in Thailand is mainly characterised by the change of forest areas to non-forest areas. In this, forest areas are largely converted to agricultural lands. Classified map of 1985/86 has been presented in Map. 3. The table below shows the major land cover types and extent of Thailand in 1985/86.

Change analysis was performed by overlaying 1985/86 and 1992/93 classified land cover maps. Major land cover change in Thailand is attributed by the conversion of forests to non-forest areas particularly that of crop lands. The spatial location of change areas are presented in Map. 4. From the analysis, it was found that within the span of 7 years, 2335085 ha. of forest area has been changed to agricultural lands. The estimate is not precise in the sense that conversion of forests to severely degraded forests is also included in the croplands due to its similar spectral signature. Further investigation is recommended in these change areas, preferably using multi-seasonal and multi-temporal high resolution satellite data.

4.3 GIS Database

During the analysis of the satellite data, a number of data layers have been prepared and used. Some of these are presented in Appendix 1.

4.4 Policy Implications

Since the establishment of Royal Forest Department in 1886, a number of efforts are in place to conserve the forests and forest Biodiversity of Thailand. The policies designed in early days were focused on the problem of excessive, unregulated teak harvesting. Selective harvesting of the trees was allowed from the very beginning and it is still being practised. Reforestation was initiated in 1906 and was widely practised by 1910, however, up to the present time, the area reforested under this policy has only been about 3 million rai (Onchan, 1993).

Forest policies were given due consideration in all National Economic and Social Development Plans, started in 1961. This is in recognition to the fact that forest resources are directly and indirectly beneficial to the economic and social development of Thailand. In the fourth National Economic and Development Plan (1976-1981), strong emphasis was given to conserve at least 40% of the total area of the country under forest cover. Due to the political, economic and social pressures, the goal was not realised (Klankamsorn and Cgarupat, , 1994). The target was once again highlighted in the seventh five year plan (1992-97).

In 1985, National Forest Policy was formulated which was different from previous policies. It emphasised interagency co-operation, involvement of the private sector, improved and flexible administration and so on. In 1987, The Royal Forest Department classified the mangrove land use zone and established the urgent strategic management measures for the mangrove forests and coastal resources including coral reefs. Other policy measures include the nation-wide ban on logging in 1989, first conference on Biodiversity in 1989, the initiation of forest zoning in 1989.

With all these initiatives, the rate of deforestation in Thailand is decreasing at a decreasing rate.