Aboveground Biomass and C Pools in Pasture Chronosequences Along a Climatic Gradient in Costa Rica

Although land use / land cover change is an important source of C pool loss, the loss of C over time and the variation in C pool sizes among different climatic zones in primary forest to pasture conversions is little studied. We determined total aboveground biomass (TAGB) and C pools in 31 Costa Rican pastures encompassing 6 chronosequences in 6 life zones along a gradient from tropical dry forest to lower montane rain forest. TAGB varied greatly among sites, ranging from as high as 316 Mg/ha to as low as 3 Mg/ha. The large variation in pasture TAGB, both within chronosequences and across climatic zones was primarily due to remnant trees still standing in the pastures. Younger pastures from the wetter life zones tended to have higher TAGB and C pools than old pastures in the dryer life zones. These results highlight the importance of both land use history and climate in determining the potential for C sequestration in pastures.