Forests, weeds and farms

The shifting cultivation system of the Adi community in the Eastern Himalaya in Arunachal Pradesh is unique in many ways. A forest-fallow matrix in such a landscape also provides opportunities to explore vegetation succession patterns and mechanisms following a disturbance. 

Shifting cultivation has been described as a form of forest farming in which land under crops, located a practicable distance from a farming village, is often rotated annually. In north-east India, where shifting cultivation or jhum is widespread among diverse tribal communities, increasing human population density and forest loss have resulted in short fallow cycles (4-5 years is the period between two cultivation cycles) and arrested succession in many areas, often due to exotic weedy species.

The Adi community in the Upper Siang district of central Arunachal Pradesh state, largely practice subsistence shifting cultivation, with a relatively lesser area under terrace cultivation. The objectives of this research are: 1) to understand the diversity of the shifting cultivation practice of the Adi community in selected villages and to examine if this affects the forest cover surrounding the villages, 2) to understand the patterns and processes of vegetation recovery following shifting cultivation, 3) to investigate effects of an invasive exotic species Mikania micrantha on native plant regeneration and to explore ways to control invasion by the species.

Although shifting cultivation is a widespread practice in several parts of India, government policies have attempted to replace it with other land uses, specifically settled agriculture and monoculture plantations. What factors determine if a community can make the shift? Through interviews with the Adi tribe in Central Arunachal, we tried to identify these factors.  Our research shows that although settled cultivation was initiated in the 60s, about 90 % of the families still practise shifting cultivation. We documented 13 festivals, following an annual agricultural calendar, associated with this activity. Furthermore, we found that the economic status of a household may determine whether a family shifted to  settled cultivation. Disregarding this, government policies since the British colonial period have focused on introducing settled cultivation and cash crop options, unmindful that local institutions have internally regulated the practice. The shift to settled cultivation may entail significant economic and cultural costs, which are ignored in the Government policies. Future policies should be mindful of these factors and not use a one-size-fits-all strategy.

What is the impact of a cycle of clear-felling and cultivation on forest regeneration in Asian tropical forests? We examined forest recovery patterns by comparing species composition, richness and forest structure in early and late fallows formed following shifting cultivation in the Siang region. We examined changes in functional traits of tree species to understand recovery processes with succession. Tree species richness and basal area was higher in fallows with longer cycles. Species composition recovery, however, was low; with even the oldest fallow (50-year fallow) being less than 50% similar to uncut forest in terms of composition. Successional sites that recover over long periods may differ compositionally from uncut forest within a shifting cultivation landscape as these forests are often prone to other anthropogenic disturbances. Functional trait analysis revealed that early fallows were colonized by tree species that are animal-dispersed, insect-pollinated with small fruits and seeds, whereas uncut forest and late successional forests were dominated by species that were tall, self-dispersed, wind-pollinated and of high wood density that are dominant mature forest species in the Himalaya.