Carbon storage and sequestration of re-growing montane forests in southern Ecuador

The storage and sequestration of carbon by tropical montane forests is poorly understood. We quantified the above-ground biomass (AGB) storage in secondary tropical montane forests in southern Ecuador. The AGB in older secondary (>40 years old) forest was found to be 158 ± 38 Mg ha−1 of land surface at 1000 m elevation and 104 ± 25 Mg ha−1 of land surface at 2250 m elevation. This is less than the storage reported in a recent synthesis of AGB observations in mature tropical montane forests, potentially due to a legacy of selective logging within our study sites. The slope angle resulted in AGB being 1.5-10% greater when reported on a planimetric compared to land surface area basis. We also quantified AGB in areas of abandoned pasture where grazing and fire had been excluded. Pasture that had been recently abandoned (1-2 years) stored 2-18 Mg ha−1 of AGB with the higher values due to the presence of relict trees. Re-growing secondary forests, established through natural regeneration, accumulated AGB at a rate of 10 Mg ha−1 yr−1 at 1000 m elevation and 4 Mg ha−1 yr−1 at 2250 m elevation, for the first 5-7 years after pasture abandonment. After 12-15 years, accumulation of AGB slowed to 1-2 Mg ha−1 yr−1. Net biomass accumulation rates were similar to those observed in lowland humid tropical forests, suggesting that regenerating tropical montane forests provide an important carbon sequestration. In newly regenerating forests, small trees (DBH < 10 cm) contributed up to 50% of total AGB. In the older secondary forest at high elevation coarse dead wood contributed 34% of total AGB.