Recovery of tropical rainforest avifauna in relation to vegetation succession following shifting cultivation in Mizoram, north-east India.

Abstract

A study was conducted at Mizoram, north-east India to investigate the recovery of rainforest bird community structure and composition in relation to forest succession after slash-and-burn shifting cultivation. Replicate fallow sites abandoned after shifting cultivation 1, 5, 10, 25 or ∼100 years ago, were compared with primary evergreen and semi-evergreen forest using transect and quadrat sampling. Vegetation variables such as woody plant species richness, tree density and vertical stratification increased with fallow age in a rapid, non-linear, asymptotic manner. Principal components analysis of vegetation variables summarized 92.8% of the variation into two axes: PCI reflecting forest development and woody plant succession (variables such as tree density, woody plant species richness), and PC2 depicting bamboo density, which increased from 1 to 25 years and declined thereafter. Bird species richness, abundance and diversity increased rapidly and asymptotically during succession, paralleling vegetation recovery as shown by positive correlations with fallow age and PC1 scores of sites. Bamboo density reflected by PC2 exhibited a negative effect on bird species richness and abundance. The bird community similarity (Morisita index) of sites with primary forest also increased asymptotically with fallow age indicating sequential species turnover during succession. Bird community similarity of sites with primary forest (or between sites) was positively correlated with both physiognomic and floristic similarities with primary forest (or between sites). The number of bird species in guilds associated with forest development and woody plants (canopy insectivores, frugivores, bark feeders) was correlated with PC1 scores of the sites. Species in other guilds (e.g. granivores, understorey insectivores) appeared to dominate during early and mid-succession. It is suggested that the non-linear relationships imply that fallow periods less than a threshold of 25 years for birds, and about 50-75 years for woody plants, may cause substantial community alteration. As 5-10-year rotation cycles prevail in many parts of north-east India, it is concluded that there is a need to protect and conserve tracts of late-successional and primary forest.

Key words

• botanical composition
• cropping systems
• cultivation
• fallow
• forest ecology
• forests
• mixed forests
• nature conservation
• plant succession
• population dynamics
• rain forests
• shifting cultivation
• species diversity
• synecology
• tropical forests
• tropical rain forests
• understorey
• vegetation types
• virgin forests
• wild animals
• wild birds
• woody plants