Optimal elevation for biomass carbon accumulation in tropical planted and secondary forests

Restoring tropical forest can provide a large additional carbon sink, yet knowledge of the optimal locations for reforestation programs remains uncertain. By evaluating multiple pantropical forest biomass carbon and height datasets, we find that tropical plantations and regrowth forests (TPFs) situated at elevations ≥ 300 m accumulate 1.5-fold more carbon per year in biomass than their lowland counterparts (elevations < 300 m) prior to reaching maturity. Notably, the biomass carbon accumulation rates increase significantly (P<0.001) between 300 m and 1000 m, subsequently declining at higher elevations. The main cause is the greater sensitivity of ecosystem production than respiration to elevational gradients in air temperature and vapor pressure deficit. Our analysis also shows that TPFs at mid-elevation (300 to 1000 m) grow most rapidly before ~20 to 25 years of age, while for those in the lowlands (< 300 m), maximum growth rates are attained at up to 30 years old or more. Our findings underscore the importance of accounting for elevation when executing reforestation in the tropics.