A meta-analytical global comparison of aboveground biomass accumulation between tropical secondary forests and monoculture plantations

Secondary forests and monoculture plantations are widespread in the tropics and are the two most common forms of reforestation. To assess the value of both systems for CO2 mitigation, we performed a systematic analysis of the two systems comparing growth rates and potential to store carbon. The increasing involvement of these forest types in carbon trading makes a pertinent issue. We used a meta-analytical approach to evaluate relative rates of aboveground growth (biomass accumulation) in secondary forests and monoculture plantations, controlling for climate and site characteristics. We find a general tendency for aboveground biomass accumulation (ABA) to be marginally higher in plantations than secondary forests. Three recorded site factors were significantly associated with ABA, but differed between reforestation types. Plantation growth rates were negatively correlated with precipitation seasonality, while growth rates of secondary forest were positively correlated with surrounding tree cover and negatively correlated with duration of prior land use. It is noteworthy that poor reporting of site history such as prior land-use duration, particularly in monoculture plantations, and a strong bias in studies towards measuring young forest plots obfuscates evaluation of some ecological drivers and long-term processes. We conclude that the difference in ABA between tropical secondary forests and monoculture plantations is smaller than previously assumed, emphasising the potential of secondary forests for low-cost carbon storage and biomass production, particularly in landscapes with high existing tree cover or highly seasonal rainfall.