Residence times of woody biomass in tropical forests

Background: The woody biomass residence time (τ_w) of an ecosystem is an important variable for accurately simulating its biomass stocks. Methods and results: We reviewed published data from 177 forest plots across the tropics and found a six-fold variation (23-129 years) in τ_w across our dataset, with a median τ_w of ca. 50 years. This value is similar to the median default value across 21 vegetation models for tropical forests, although the range of values used in models is large (20 to 200 years).Conclusions: The notion of a constant τ_w across all tropical forests may be of limited utility, given the large observed variation in τ_w. We found that while there was little relationship between climate variables and τ_w, there was evidence that edaphic factors exerted a strong influence on τ_w. In both the Neotropics and the Paleotropics, τ_w was highest in heavily weathered soils, suggesting that low soil fertility and/or non-limiting soil physical conditions exert a critical influence on τ_w. There is considerable uncertainty in how τ_w will be affected by global environmental change, especially by increased atmospheric CO₂. Even small changes in τ_w could significantly reduce the future tropical forest carbon sink predicted by many vegetation models.