Adebate goes on with regard to shifting cultivation. Is it sustainable land use or is it destructive to
the environment? There is the view that what is traditional is sustainable and what is untraditional is destructive.
There has been a change in shifting cultivation in many subtropical areas of Southeast Asia. Fallow periods have shortened
and fallow vegetation has changed from forest to herbaceous meadow. Some see this as a collapse of the traditional
system caused by population pressure and think it destructive. But is this really so?
Bakashaozhai is a village 42 km away from Jinghong in the Xishuangbanna region of Yunnan. Thirty years ago the
villagers practised a 16-year cycle of shifting cultivation which had a long period of fallow. Zhouli, an 83-year
year villager, recalls how things were like in those days.
The first two years of fallow was called the so pelu, and the vegetation which was common were yangcao
(Conyza sumatrensis) and yi (Imperata cylindrica). The third to sixth year of fallow was called so nu, and
the common vegetation were lupelu (Colona floribunda), qiazo (Eurya spp.) and pingala (Melastoma spp.).
The seventh to thirteenth year of fallow was called so ku, and the dominant vegetation was susa (Schima wallichi),
a tree which grew up to 20 m high.
In the fourteenth year, the fallow was slashed-and-burned and rice was cultivated for three years.
In shifting cultivation, weed control is an important factor determining the length of fallow periods.
When harmful perennial weeds increase, the cultivator has to wait for the perennial weeds to be suppressed
by woody vegetation. This usually takes ten years or more.
A major problem is provided by the prevalence of the perennial grass Imperata cylindrica which figures as
yi in Zhouli’s account. Belonging to the family Graminae, Imperata cylindrica is widely distributed in temperate
and tropical zones in Asia, Africa and Australia. The plant reaches a height of 1-2 m but its branching system
above the ground is not developed like other grasses. However, under the ground, its rhizome is very well developed,
and because of the strong restorative ability of the rhizome it is very difficult to remove the Imperata cylindrica.
In traditional shifting cultivation systems it was necessary to wait ten years or more so that trees would grow high
enough to remove the Imperata cylindrica by shading.
The change to a shorter period of fallow in Bakashaozhai was made possible by the invasion of Euporatium odoratum
into the region. A perennial herb of the family Compositae, Eupatorium odoratum originated in South Africa and spread
to Southeast Asia in the 1950’s and is now found in most of the tropical and subtropical areas of the world. The
well-branched stems reach 2-3 m in height and the leaves and stems are toxic to livestock. There is no rhizome and
once the plants are pulled out or killed by herbicide no more shoots emerge.
In the fallow system currently practised in Bakashaozhai, there are annual herbs (Conyza sumatrensis), perennial
herbs (Eupatorium odoratum) and perennial grasses (Imperata cylindrica, Isachne albens Trin.) in the first year of
fallow. In the second year, the annual herbs disappear and there is a significant decrease in species diversity.
The Eupatorium odoratum competes against the Imperata cylindrica, and from the third year on, dominates. The
Imperata cylindrica is removed without the need for a long period of fallow.
Returning to the debate, Is shifting cultivation sustainable land use or is it destructive to the environment?
Is it the traditional which is sustainable and the untraditional which is destructive?
Herbs, including Eupatorium odorata, and annual grasses occur in the cultivated fields, but very few perennial
grasses. The herbs are easily removed by the spraying of 2-4-D, a herbicide which kills only non-grass plants and
does not damage the rice. The annual grasses, unlike perennial grasses with rhizomes, do not pose a problem and are
easily pulled out by hand. Thus, in the present system of shifting cultivation, Eupatorium odorata suppresses Imperata
cylindrica, and is then easily killed by the use of herbicide, allowing rice to be grown without competition from
grass or herb.
Now, in Bakashaozai, the fallow is slashed-and burned after five years of fallow. Upland rice is then cultivated
continuously for three years or, alternatively, rice is cultivated in the first two years and maize in the third.
After the three years, the fields are left fallow again.
One thing seems to be clear at Bakashaozhai. It is not population pressure which has produced the change in shifting
cultivation. Population density is low here and natural forests still remain. The motivation for shortening the
fallow period came from the wish of the villagers to shorten the time that they take to commute to their fields.
With a long fallow period, they had to commute to distant fields Some old villagers say that in the old days of
the long fallow period it took them several hours to get to their most distant fields. The change to a shorter
fallow period has very much cut down the time that they take to go to their fields.
It does not seem that there is land degradation with the shorter fallow period in Bakashaozhai.
The new system of shifting cultivation has been practised for thirty years now, that is, for four cycles, but the
yield is still good. The villagers of Bakashaozhai have an exact knowledge of the area of the fields that they work,
as well as of the yield, and the current yield works out at 3-4 tons per hectare.
Bakashaozhai is only one example of the change that is taking place in shifting cultivation. Elsewhere, seeds of
alder (Alner neparensis) are broadcast in Nujian in Yunnan, and seeds of shrubby legume are broadcast in Northern
Laos to bring about the change. The question of whether this change is destructive or contributes to sustainability
needs to be studied and understood before hard positions are taken.