Keywords: Shifting Cultivation, Laos, Impact Analysis, GIS, Remote Sensing
Abstract
MOS-1 satellite image and 40 points of soil samples are analyzed to
identify the distribution of shifting cultivation and GIS technique was applied to
evaluate the environmental problems for Nam Khane watershed. The land use
classification map was prepared and the values of each land use area by elevation level
and soil property were produced respectively.
Excessive agricultural activity of shifting cultivation in the Nam Khane
watershed not only decreased the forest area, but also changed the primary
forest into secondary woodland of shrub. On the phase of soil property, it
accelerated the soil and gully erosion, and acidification. To solve these
environmental problems, the most import step is to settle the agriculture from
shifting cultivation to permanent cropping.
1. Introduction
The Nam Khan River runs about 90km along the westward of northern
mountain area of Laos and joins the Mekong River near Luang Prabang, the
second largest city in Laos. The wide area of shifting cultivation in Nam Khan
watershed has been causing the destruction of forest and soil.
The seriousness of food shortage and environmental problem of this area led to the
research team for the watershed management of this area by UNCRD (United Nations
Center for Regional Development) from April, 1992. And the author was a number of it
covering the natural environments and image analysis of satellite images. The research
lasted through February, 1994, and topographic map(1/50,000), aerial photos, satellite
image, geological map of that area have been analyzed. Its soil, topography, vegetation,
agricultural method have studied through four times of ground survey, and interview
survey among the villagers was carried out.
This study is summing up of 1 topographic characteristics 2 shifting cultivation 3
environmental problems concerned with shifting cultivation of H.Khane watershed
which was most typically and widely analyzed among Nam Khan watershed.
2. Topographic Characteristics
The mainstream of the Nam Khane flows incised meander widely but that of
H.Khane, one of its tributary flows almost straight under the influence of
northeastern– southwestern lineament. The topography of H.Khane such as
elevation, slope, property of geologic bed rock is divided into 4 topographic
units as follow.
1. Highland (plateau): ground of pure limestone with 800-1500m of sea
level and land surface with more or less than 10% of surface slope, karst
landform has been developed on the surface with many enclosed hollow such
as doline, uvala, etc. There seems to be no surface water because almost all
water on the ground flows deep underground through sink-hole.
2. Steep slope: developed surrounding plateau, a lot of part of which is 60%
slope of outcrop rock and is found at more less than 700-1200m of sea level. Its
geology from the bottom of this to the surface of plateau is pure limestone and
the water flowed underground from the surface of the plateau through sink-hole
forms karst spring everywhere near the end part of this. The Karst spring
is the start point of first order stream and generally village is settled around the
karst spring.
3. Hill-side piedmont: piedmont eroded by first order stream with more or
less than 12% of surface slope and distributed under steep slope. Its sea level is
from 800m at right part of the Nam Khane, 600m at the left part northwestern,
to 300m roughly of the lowest figure. The geology here with Pz2 and cPz2 do
not contain CaCO3 enough to form karst landform and enclosed hollow such as
doline is not worth considering. Shifting cultivation is well developed.
4. Alluvial plains: narrowly distributed where the Nam Khane and the
H.Khane gets together with floodplains of present stream and river terrace. The
average degree of slope is more or less than 3%
3. Forest Damage with Shifting Cultivation Area
3.1. Practical Situation
Shifting cultivation is an agricultural method in which the seed is put in the
holes on the surface after cutting down and burning the trees during the dry
season for one to two years and moved to another place because of productivity
decrease.
Shifting cultivation is popular in the mountain area of northern Laos with a
little alluvial plain but many piedmont hills with gentle slope. Consequently
about no more than 10% of primary forest remains intact and 1/4 of the rest is
now being cultivated and shrubs, bamboos deserted after shifting cultivation.
Four parcels of land are cultivated in turn because cultivation farming is started
again after burning three-year-old fallow.
The chief industry in this area is agriculture and 85% of paddy yield is
upland rice cultivated in shifting cultivation area and 15% of it is paddy
cultivated in alluvial plain. Therefore shifting cultivation plays a chief part in
the economy of this area.
There are about a little more than 70 ethnic groups are distributed and the
three main tribes are Lao Sung in high lands, Lao Theung in the middle of the
mountain, and Lao Leum in low lands. The exact number is 7745(1992.12)
which consists of 13% of Lao Sung, 59% of Lao Theung, and 28% of Lao Leum.
Lao Sung is populated on plateau and cultivates opium with the advantages of
shifting cultivation, cool climate and isolation from political power. Lao Theung
are widely populated and their chief farming is shifting cultivation and Lao
Leum in low land and dominate Laos in politics and economy.
