Decoupled recovery of soil physicochemistry, microbiome and methane sink function during secondary forest succession in the Eastern Himalayas

Secondary forests in the Eastern Himalayas are gaining importance for biodiversity restoration and ecological processes post-disturbance. As these forests regrow, the changes in soil chemistry and microbial ecosystems influence climate-related functions like methane (CH4) capture. However, the simultaneous recovery of these belowground aspects remains uncertain. Our study reveals that during a forest chronosequence in Metok, the belowground recovery unfolds on separate paths in the Eastern Himalayas.

Inorganic soil properties and microbial community structures gradually align with those of primary forests as the soils become more acidic. Nonetheless, soil organic carbon, microbial diversity, and bacterial counts recover by the 25-year mark but then diverge again by the 40-year point. The co-occurrence networks of soil organisms begin resembling those of primary forests by the 40-year point, yet the core species sustaining them are unique to each stage.

Atmospheric CH4 absorption experiences fluctuations: it returns to primary forest levels within 25 years of reforestation but declines in 40-year stands, matching the capture rates of recently disturbed 5-year forests. Instead of the usual methane-removing microbes, four distinct microbial variety—three belonging to the genus Mycobacterium—show a strong association with CH4 flow.

They function as central nodes or connectors in the co-occurrence networks, requiring further genomic and experimental research to understand their roles. The apparent restoration witnessed within the initial 25 years should not be equated with long-term success. This emphasizes the necessity for extended chronosequences and regular monitoring to fully comprehend the complexities of secondary-forest recovery.