Viet Nam 2.Results

The seasons for agricultural crop harvesting and summer period were generalized into two groups which served as one of the important guidelines in acquiring the multi-temporal data of AVHRR. It was ascertained that from November until late January the harvesting of major crop such as rice where generally practiced in the country, and in order to capture the seasonality of the forest vegetation images from February until April were recorded. Moreover, the availability of other ancillary data such as elevation, natural resources map of Vietnam have contributed additional knowledge in the process of satellite data interpretation. All AVHRR images that correspond to the generation of the land cover information of Vietnam are listed in Table 1.

Table 1. Acquired NOAA AVHRR LAC data for Cambodia

Harvest Season	Source	Summer Season	Source
i) 1985-1986
09 January'86	NOAA/NESDIS	15 February'86	NOAA/NESDIS
18January'86	NOAA/NESDIS	25 February'86	NOAA/NESDIS
		27 February'86	NOAA/NESDIS
		06 March'86	NOAA/NESDIS
		25 March'86	NOAA/NESDIS
ii) 1992-1993
13 December'92	EDC	15 February'93	EDC
30 December'92	NOAA/NESDIS	17 February'93	EDC
30 January'93	NRCT	05 March'93	NRCT
		24 April'93	NOAA/NESDIS

2.1.1 Spectral Characterization and land Cover Mapping 2.1.1.1 Classification Scheme

The interpretation of the NOAA AVHRR data covering Vietnam (see Appendix 1) identified eight major landcover divisions. Site specific classes like marshes and mangrove are mainly found in Mekong Delta. Forest land has been categorized either evergreen or deciduous formation, and other group of landcover like scrubland, agricultural area and water bodies are also noted. Table 2 and Map 1 show the aerial extent and spatial distribution of various landcover types of Vietnam.

i). Evergreen Forest (EVG) - these forest is multi-level with an undergrowth of shrubs and natural regeneration. Trees of Dipterocarpaceae family often dominate the upper storey, sometimes reaching a height of more than 50 m. Other families represented in the upper storey are Ebenaceae, Luguminosae, Guttiferae and Meliaceae.

ii). Deciduous Forest (DEC) - they are dominated by species of the genus Lagerstroemia and constitute a transition between closed evergreen forest and woodlands. Bamboos constitute the natural undergrowth of deciduous formation, they also invade abandoned farm lands.

 iii). Mangrove (MGV) - they occupy large areas in the extreme south of Vietnam near Ho Chi Minh City and small patches at the Red River delta. Species of the genera Rhizophora and Bruguiera account for three quarters of the well-developed-stands.

 iv). Marshes (MRS) - they grow in areas more or less permanently covered by fresh water. The following species occur in this category: Eugenia elaeocarpus, Sterculia, Adina cordifolia, Calophyllum inophyllum as well as numerous species of palm trees. Homogenous stands of Malealeuca leucadendron occur behind the mangroves in areas not reach by brackish water.

 v) Scrubland (SCR) - normally after forest destruction, an open shrubby vegetation develops with sporadic distribution of trees with grasses on the ground.  vi). Agriculture (AGR) - cultivated fields that consist mainly of paddy fields, either irrigated or rainfed. It corresponds also to the less vegetated surface that includes abandoned fields and exposed soil during the dry period.

 vii). Water (WTR) - represented by lake, rivers and water depression that occurs at the alluvial plain.

 viii). No Data Available (NDT) - this is to designate those covered by clouds and some topographic effects such as mountain shadow.[Top]

Table 2. Land Cover Types and Extent of Vietnam, 1992-1993.

LAND COVER CATEGORY	Area (sq.km.)	%
Evergreen Forest	80303.3	24.7
Deciduous Forest	11348.6	3.5
Mangrove Forest	1150.4	0.4
Marshes	6039.2	1.9
Scrubland	162841.0	50.1
Agriculture	60886.5	18.7
Water Bodies	1393.3	0.4
No data available (Cloud covered)	1278.4	0.4

2.1.1.2. Land Cover Distribution and Assessment

The interpreted land cover map of Vietnam from the 1992-1993 NOAA AVHRR data estimated that 27% of the whole country is covered by evergreen and deciduous forests. The western plateau and coastal region in the central part of Vietnam hold the large tract of land covered by this two type of forest. Provinces of Gia Lai-Kontum and Dack Lac which all belong to the western plateau zone hold the largest dense evergreen and deciduous forest of the country (see Table 3). Nghe Tinh and Lai Chau provinces were considered as the most forested region in the Northern Mountains of Vietnam. However, the scrubland which is composed of shrubby vegetation in association with grassland and isolated trees covers an approximate area of 162,841 sq.km., half (i.e., 50%) of the entire country. It is widely distributed but commonly found in the northern region of the country.

Two big patches of agricultural lands comprising around 19% of the total area, are the major landscape unit in Red River and Mekong Deltas. Small and narrow strips of land along the coastal area are also devoted for this kind of land use. Additional categories of landcover were disclosed at the Mekong Delta, tract of marshes and mangrove. The province of Minh Hai is where the majority (67%) of remaining mangrove forests thrive. Close to the major tributaries of the Mekong River lies group of tall grasses with isolated trees or bushes which composed the marsh ecosystem. A place where it is periodically inundated by water and provide sanctuary for a diverse forms of wildlife. Provinces of Kien Giang and Loang An share the largest contiguous tract of marsh land. Very large seasonal variations in river flow have a decisive impact on both fauna and flora on marsh lands.

Altitudinal distribution of the evergreen forests suggests that it dominates a wide range of elevation level from 100 m to 1300 m, few patches are located in more than 1300 m above sea level and also on flat area. The deciduous formations are normally found in 200 m up to 700 m along the central plateau of the country, and rarely observed in a much higher elevation gradient. The scrubland typically noticeable from the flat terrain up to middle elevation (i.e., 900 m). Large proportion of the country's low lying areas are devoted for agriculture, however, significant fragments are situated in elevation higher than 500 m.

Table 3. Land Cover Type and Population Distribution for Different Provinces of Vietnam: 1992-1993

Note: * - Source: Vietnam, The Situation of Children and Women, UNICEF, 1990

** - It is now sub-divided into 3 provinces (Quang Binh, Quang Tri and Thua Tien Hue)

*** - It is now sub-divided into 3 provinces (Quang Ngai, Binh Dinh and Phu Yen)

Where:

EVG - Evergreen Forest AGR - Agriculture

DEC - Deciduous Forest WTR - Water Bodies

SCR - Scrubland NDT - No Data Available

MGV - Mangrove MRS - Marshes

2.1.2 Agriculture and Population

Vietnam being the most populated country in Indochina (67.6 million, 1991 estimate) distinctively characterized by the presence of intensive pressure on land where the large group of populace are located. The populated provinces in two deltas signifies large proportion on the country's cultivated area (see Table 3). Similar trend can also be observed for the increasing scrubland formation with few exception on provinces in the western plateau which is attributed to the physiographic locale and climatic condition of the central highland.

2.2 Accuracy Assessment

Spatial and seasonal variations have noted upon comparing the AVHRR interpreted 1992-1993 Landcover map for Vietnam and available 1991-1993 LANDSAT TM imageries (14 February 1991 - 04 October 1993). Majority of inconsistencies were exhibited from the scrubland category. The small agricultural holdings practicing different cropping pattern and cycle regardless of the elevation apparently classified under that shrubby formation. Commercial plantation, on the same hand, inaccurately falls under that category. The evergreen forest both governed by varying density and sporadic mode of distribution (e.g. small hills along the

Another spatial variation occurred by interpreting a tract of dense forest as scrubland in a vast limestone area in the central region of Vietnam. The distinct signature displayed by the exposed limestone with vegetation appeared to be less in terms of chlorophyll activity in order to be classified as evergreen forest. The distinct boundary between mixed deciduous and evergreen formations is rather difficult to ascertain in the AVHRR interpretation. On a flat terrain, portion of agricultural area tends to be classified as marshes once the later is dominated by dense and tall grasses. However, irrigated field also became similar with an open marsh land. Bare agricultural fields became synonymous with sands along the coastal area.

Seasonal variation contributes in identifying deciduous forest as scrubland. An image taken during the peak of summer season (e.g., 05 March 1993) gives the minimum cloud coverage but also the shedding of leaves decreases the chlorophyll level of a certain group of trees to be identified as deciduous forest. Burnt surface of the deciduous forest tends to be similar in signature with scrubland and even an open agricultural land.

The above observations could served as additional guidelines in the future interpretation of satellite data for Vietnam. Nevertheless, the above irregularities only represent 24% error margin of the generated 1992-1993 landcover map of Vietnam (see Table 4). [Top]

Table 4. Map Accuracy of Vietnam's 1992-1993 Land Cover

Overall Mapping Accuracy (M.A.) = 75.8% 2.3 Land Cover Monitoring: 1985-1986 and 1992-1993

The land cover change exhibited by comparing interpreted land cover maps from the time series analysis of 1992-1993 and 1985-1986 (see also Table 5 and Map 2) AVHRR data can also be viewed in terms of its nature and geographical aspect. The gradual transformation of the closed forest into a scrubland formations and from scrubland to give way for additional agricultural land are observed. The northern highland where the density of population is relatively high and the plateau of the central Vietnam showed such nature of land cover modification. The forest cover change in the northern region is normally exemplified by the gradual shrinking of the forest boundary against the expanding scrubland formations. However, the central region where the large proportion of the country's forest cover is compounded not only by the decrease of hectarage and also an abrupt transformation from dense form of vegetative cover (e.g., evergreen) into a much lower form of vegetative cover (e.g., scrubland). The seasonal degradation of vegetation index value in the central highland tends to be similar to the large area of deciduous formation of Cambodia where annual fire is persistent.

Table 5. Land Cover Types and Extent of Vietnam, 1985-1986.

LAND COVER CATEGORY	Area (sq.km.)	%
Evergreen Forest	84930.1	26.1
Deciduous Forest	14932.9	4.6
Mangrove Forest	1306.9	0.4
Marshes	8778.9	2.7
Scrubland	145246.5	44.6
Agriculture	56348.5	17.3
Water Bodies	1957.2	0.6
No data available (Cloud covered)	11835.4	3.6

Expansion of agricultural land is apparent from the decreasing extent of the marsh land especially in the Mekong Delta. It is reported that most people in this delta are engaged directly or indirectly in agriculture. Moreover, this delta accounts for a high share of national agricultural production and generate over 40% of all agricultural output (Thanh, 1993). On the other hand, the extent of agricultural area in Red River Delta do not exhibit significant change over the duration of seven years. Group of at least 9 sq.km. of cultivated lands are also distributed in the northern eastern and central highlands of the country. The proliferation of commercial plantations has contributed to the increasing proportion of the scrubland category. Lastly, two additional dams were observed, one in the north and one in the south.

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In this Report
	Introcution
	Results
	Conclutsions
	Abbreviations

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