Residence times of woody biomass in tropical forests

Background: The woody biomass residence time ((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 (23129 years) in (w) across our dataset, with a median (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 (w) across all tropical forests may be of limited utility, given the large observed variation in (w). We found that while there was little relationship between climate variables and (w), there was evidence that edaphic factors exerted a strong influence on (w). In both the Neotropics and the Paleotropics, (w) was highest in heavily weathered soils, suggesting that low soil fertility and/or non-limiting soil physical conditions exert a critical influence on (w). There is considerable uncertainty in how (w) will be affected by global environmental change, especially by increased atmospheric CO2. Even small changes in (w) could significantly reduce the future tropical forest carbon sink predicted by many vegetation models.