An Impact Analysis of Shifting Cultivation in the Forest of Northern Laos using GIS and Satellite image

3.2. Satellite Image Processing
Shifting cultivation has been causing serious environmental problems in the area but it has not been estimated at all how much area has been destroyed and which part is in the most serious condition by the government. Besides annual shifting makes the statistic survey more difficult. In order to figure out the distribution of shifting cultivation area, land cover classification was performed using satellite images.

The satellite image used is MOS-1 MESSR and its pixel size is 50m. Performing geometric correction according to UTM using ERDAS and making false color composite after cover RGB filter on 4/2/1 band produced (Photo 1).

The red part in the photo shows present primary forest, which is partly distributed on plateau and steep slopes. The light red part is fallow, which includes the secondary forest of shrubs, bamboo of fallow after shifting cultivation. The blue part is present shifting cultivation area and the green part of plateau is the opium cultivation area. The long and narrow white part along to the Nam.Khane is paddy field of alluvial plain.

But classification of images was performed because the borderlines between classes are not clear and the accurate data are not available with false color composite. The area was classified into 6 classes of shifting cultivation area, opium, fallow, forest, water, paddy field through aerial photos and ground survey. The result of supervised classification selected about 2-9 training areas each class through maximum likelihood classifier method is as (Photo 2). As is shown in (Photo 2), opium is chiefly distributed on plateau, shifting cultivation is on piedmont, and paddy field narrowly along the Nam.Khane.

The size of the areas according to the class/elevation are calculated by overlaying the thematic maps of each elevation on this chroplethe map using Arc/Info GIS Software.

On the whole fallow occupies the largest area of 47.1% and forest occupies 20.9%, or about 1/5 of the whole area. Shifting cultivation area, which is more or less than 13%, is almost as large as opium cultivation area and paddy field occupies only 4%. Shifting cultivation area is chiefly distributed at the elevation of 400-800meter and so is fallow which is deserted after shifting cultivation.

Photo 1. False color composite of H.Khane basin with MOS-1 image

Photo 2. Land use classification map of H.Khane basin

Table 1 Soil content analysis of H.Khane basin

Grain Size PH OM C/N Nitrogen
Sand Silt Clay HO KCI Total N-NH₃ N-NO₃
Paddy
Field
Upland
Rice
Mixed Forest
Vientiane
Plain
(%) (%) (%) (%) (%) (%) (%)
33.85 36.71 26.49 7.49 6.98 2.35 8.06 0.170 24.13 12.04
25.03 41.11 33.87 5.62 4.95 2.91 7.33 0.219 23.92 9.80
32.53 39.28 28.16 6.35 5.89 3.08 7.92 0.222 27.35 12.12

62.40 25.90 11.70 6.30 5.50 0.57 15.0 0.022 14.00 7.00

Phosphorous Potassium EC CaCO₃ Exchangeable (mg/100g of soil) CEC-S Fe₂O₃
P P₂O₅ KO KO Ca++ Mg++ K+ Na+
(mg)
1.10
1.005
1.25

8.02
(%)
0.035
0.037
0.039

0.012
(%)
0.90
0.90
0.86

0.09
(%)
8.19
15.21
19.05

28.0

150.59
53.33
100.41

42.60
0.17
0.23

21.52
4.51
11.54

1.47

1.62
2.03
2.53

0.55

0.20
0.40
0.40

0.06

0.28
0.20
0.22

0.12

23.50
9.10
14.68

2.20

0.025
0.017
0.023

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