Recovery Process of Fallow Vegetation in the Traditional Karen Swidden Cultivation System in the Bago Mountain Range, Myanmar (<Special Issue>Ecological Resource Use and Social Change in the Minority Regions of Myanmar)

Abstract

Forests in Myanmar have a long history of teak (Tectona grandis Linn.) production, which can be traced back to the age of the English rule in the 19th century, when forests in Myanmar were categorized into those for timber production and those for other uses. Many farmers such as the Karen people, who were swidden cultivators, inhabited the forests. Therefore, the government established the "Karen Area" in the late 19th century, permitting swidden cultivation (shifting cultivation) for their self consumption. Short cultivation, long fallow swidden cultivation has been continued for over 100 years in the areas. We surveyed fallow vegetation and total carbon and nitrogen after swidden cultivation by Karen people in the Bago mountain range and compared with those in natural teak forests under selective logging systems. We set 9 circular plots 20 m in radius at fallow stands of various ages. Trees were identified and measured by diameter at breast height (DBH). Surface soil was sampled at 0–5 cm.The amounts of total carbon and nitrogen in soils varied among the plots, but no stand age dependency was observed. Grass and herb species such as Chromolaena odoratum and Thysanolaena maxima were dominant and comprised the maximum biomass in 1- and 2-year fallows. Bamboo species such as Bambusa polymorpha and Bambusa tulda rapidly recovered after grass and herb species, and the bamboo biomass in the 5-year fallow was nearly equivalent to that in over-40-years fallows. Tree species recovered to nearly the same biomass level as that of bamboos in the 10-year fallow, and further facilitated the increase in the above-ground biomass. Xylia xylocarpa was the most common tree species while species such as T. grandis might be excluded from the fallow vegetation cycle. On the whole, swidden cultivation with a short cultivation period of 1 year and over 12-year fallows maintained sufficient fallow vegetation recovery to sustain continuous swidden cultivation in the Bago mountain range.