Breaking down to build up: Litter decomposition drives soil organic carbon accumulation in young secondary forests

Abstract

Rapid deforestation in the tropics reduces the global carbon sequestration and storage capacity of forests. However, abandoned lands can recover naturally through secondary succession. While soil organic carbon (SOC) represents the largest carbon pool in young secondary forests, its drivers remain poorly understood. Here, we assessed the roles of environmental conditions (macro- and microclimate) and forest attributes (biomass and litter nutrients) in determining three key ecosystem processes (litter production, decomposition, and soil respiration) that influence SOC dynamics in secondary forests. We collected data from young secondary tropical dry and wet forests (2.3-3.6 years old) in Ghana. Wet forests had higher aboveground biomass, soil temperature and moisture, and litter production, whereas dry forests had higher litter nutrient concentrations and faster decomposition rates. SOC and soil respiration rates were similar between forest types. Structural equation modelling showed that (1) litter decomposition increased with litter production, litter nitrogen concentration, and soil temperature (rather than soil moisture), and (2) decomposition was the only significant driver of SOC. These findings highlight the central role of litter decomposition in building SOC during early forest succession and the indirect influence of climate on belowground carbon dynamics through its effects on litter quantity and quality and microclimate.