Carbon stocks and accumulation rates in tropical secondary forests at the scale of community, landscape and forest type

• Carbon stocks in secondary forests are positively correlated to the number of years recovering and negatively to LU-intensity.
• Carbon accumulation rates decrease with age but are positively correlated with LU-intensity.
• Land-use intensity is important only in the younger plots, as land was first occupied about 40 years ago.
• Secondary forests in southern Mexico recover original biomass densities in about 60–100 years.
• Secondary forests in southern Mexico have a high potential for mitigating greenhouse gas emissions.

Rapid increases of secondary forest areas in the tropics make understanding of their carbon dynamics critical to estimate net CO2 emissions and uptake. This understanding is needed for performance based mechanisms that aim to halt global warming (REDD+). Despite the importance of secondary forests to global C cycling, the impacts of recovering secondary vegetation on C dynamics are poorly understood. We present carbon stocks and accumulation rates in biomass and soil pools, using as a basis of analysis 87 sampling plots established along a secondary forest chronosequence derived from shifting cultivation. We test the influence of age, land-use intensity (prior land-use history) and two site quality indices on the size of the C stocks and C accumulation rates. Biomass and Total C pools were positively correlated with age and negatively with LU intensity, whereas C accumulation rates had opposite signs for both parameters. Soil C did not show any variation along the age gradient, but C in the upper 20 cm was positively correlated to both site quality indices. The LU-intensity influenced the tree C stock in the younger plots. We propose a nested approach in which detailed studies can be up-scaled to landscape and regional estimates of carbon pools in forest fallow and undisturbed forests and carbon accumulation rates in forest fallow.