Changes in Carbon Sequestration by Reforestation of Abandoned Costa Rican Pastures: A Carbon Inventory Using Aboveground Biomass Measurements

Tropical forest degradation is known to contribute almost 15% of anthropogenic greenhouse gas emissions through the clear cutting and burning of aboveground biomass (AGB) (Houghton 2007).  While the amount of carbon that has been released from these forests is known with relatively strong certainty, estimates of carbon sequestration and carbon storage in these tropical areas still lack confidence (Fonseca 2011). This study examines controlled reforested plots 13 years post establishment, in terms of carbon sequestration compared to untreated abandoned pasture. Work was carried out in a young secondary forest (originally a plantation of 21 different native species) and abandoned pasture plots within the Organization of Tropical Studies, Las Cruces Biological Station located in tropical premontane Southwestern Costa Rica.  Several AGB estimates were measured within each plot type and converted to carbon content estimates per plot type; combined estimates gave a forest TAGB and carbon content value. In the plantation plots, AGB measurements were taken of different pools- downed wood, trees, and herbaceous understory.  Abandoned pasture carbon content was quantified through finding the AGB estimates of the pasture grass that dominates abandoned pasture areas.  Although results varied on the equation model and data perimeter applied, the area showed to be a high performing secondary forest even with the lowest estimate of 194 Mg/ha of AGB and 97 Mg/ha of carbon. This study has found this secondary forest to be high performing for both its age and in comparison to other young neotropical secondary forests from similar and different climatic zones.