4. Environmental Problems by Shifting Cultivation
4.1 Forest Degradation
excessive agricultural activity of shifting cultivation bit into the forest, changed
into primary forest of trees into the secondary woodland of shrubs and bamboo
and decreased of the secondary forest. These problems are because shifting
cultivation could cause more serious flood and serious soil erosion.
4.2 Soil Degradation
When the slopes covered with thick rain forests become bare from shifting
cultivation,
the soil becomes barren from the erosion by rain wash and the topography is
destroyed from erosion by gully. As drainage network analysis reveals, the
bifurcation of the first order stream is over 6 value so that gullies are being
accelerated recently.
To find out the features of the soil of this area, 15, 12, 13 soil sample from
paddy field, upland rice, and mixed forest were analyzed by Vientaine Soil
Survey of Laos. The analysis of the grain size, pH, chemical content of each
place is shown on Table <1>. The result of Vientaine plain, which had been
made before, was presented here to be compared with the soil of the study area.
The result can be summed up as follows.
(1) The acidity of shifting cultivation is much higher than that of paddy field
and mixed forest area. That is because much base was lost from shifting
cultivation.
(2) Quite a little CaCO3 is accumulated in the shifting cultivation area and
mixed forest area as much as 42.6% of CaCO3 is accumulated in alluvial
paddy field. Amount of CaCO3 from the slope is small because of leaching,
however, in the alluvial plain, the amount of it is too much which
accumulated from slope and causes low productivity.
(3) The lowest CEC of shifting cultivation area shows poor condition of the soil
degraded soil.
To sum up the problem of degraded soil, the soil in the slope was eroded into
barren acid soil while the topography was changed into bad land by gully
erosion. Meanwhile, paddy field become less productive with excessive
accumulation of CaCO3 from the slopes, elevated the river bed causes frequent
flood and inundation and dirty water brings about sanitary problem of water
quality.
5. Conclusion
Nam Khane watershed, in the Northern Laos, consist of limestone plateau
surrounded with steep slope (above 1000m), wide piedmont hill land(300-
700m) and narrow alluvial plain. Opium on the plateau and up-land rice on the
hill-side are cultivated for each, but its shifting activity, which degrades the
forest and soil, has caused the serious environmental problems.
MOS-1 satellite image and 40 points of soil samples are analyzed to identify
the distribution of shifting cultivation and to evaluate the environmental
problems for Nam Khane watershed. The land use classification map is
presented on the photo 2, and the value of each land use area by elevation level
and soil property are showed on the table<1>.
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.
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