Litterfall and Decomposition in Relation to Soil Carbon Pools Along a Secondary Forest Chronosequence in Puerto Rico

Secondary forests are becoming increasingly widespread in the tropics, but our understanding of how secondary succession affects carbon (C) cycling and C sequestration in these ecosystems is limited. We used a well-replicated 80-year pasture to forest successional chronosequence and primary forest in Puerto Rico to explore the relationships among litterfall, litter quality, decomposition, and soil C pools. Litterfall rates recovered rapidly during early secondary succession and averaged 10.5 (± 0.1 SE) Mg/ha/y among all sites over a 2-year period. Although forest plant community composition and plant life form dominance changed during succession, litter chemistry as evaluated by sequential C fractions and by ¹³C-nuclear magnetic resonance spectroscopy did not change significantly with forest age, nor did leaf decomposition rates. Root decomposition was slower than leaves and was fastest in the 60-year-old sites and slowest in the 10- and 30-year-old sites. Common litter and common site experiments suggested that site conditions were more important controls than litter quality in this chronosequence. Bulk soil C content was positively correlated with hydrophobic leaf compounds, suggesting that there is greater soil C accumulation if leaf litter contains more tannins and waxy compounds relative to more labile compounds. Our results suggest that most key C fluxes associated with litter production and decomposition re-establish rapidly—within a decade or two—during tropical secondary succession. Therefore, recovery of leaf litter C cycling processes after pasture use are faster than aboveground woody biomass and species accumulation, indicating that these young secondary forests have the potential to recover litter cycling functions and provide some of the same ecosystem services of primary forests.