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.
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 muti-temporal/multi-seasonal NOAA AVHRR HRPT data it was found the the forests cover 30.17% of the total land area of Thailand. This includes both evergreen, deciduous and mangrove forests. Croplands is 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 Fig. 4 below.
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 is presented in Table 4.0.
Much of the remaining forest areas are left in northern region of Thailand adjoining Lao P.D. R., Myanmar and the People Republic of China. Other patches of forest land can also be visualised in the Peninsula despite the fact that much of the area is covered by persistent cloud cover. Other forest areas are dispersed in the central and north-eastern part of the country (Map. 1).
Forest areas thus obtained was verified with composite NDVI image. NDVI image of 31 January, 1993 is presented in the Figure 5 below.
Fig. 4 : NDVI of 31 January 1993
Distribution of forests and population according to the region are presented in Table 5.0
*population data source : Statistical Year Book - 1994
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 associate
land cover types are presented in Map 2. It is noticed that some of the
protected areas are encroached or affected by agricultural activities.
Map 2 Protected Area Distribution
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.
Although forest concession was banned since January 1989, about 0.24
million hectares of forest area had been depleted during 1985/86 to 1992/93.
The major causes of the forest degradation is encroachment, shifting cultivation,
commercial logging and forest fire. The reason for the mangrove forest
destruction is due to shrimp farming, salt farming, expansion of agriculture
lands and mining.
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.
During the analysis of the satellite data, a number of data layers have
been prepared and used. Some of these are presented in Appendix
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.