Above and belowground carbon stock of pine plantations and native oak forests coexisting in central Spain

Abstract

Promoting nature-based carbon sinks may contribute to minimise global warming. Different forest types may have different carbon sink capacity. Many areas of central Spain are covered by coexisting patches of monospecific plantations of Pinus halepensis, established since the 1960?s, and native Quercus forest coppiced up to the 1960s. We aimed to compare the carbon stock between both types of forests, considering both above and belowground compartments. In each plot, we measured the dimensions of every adult tree, the shrub cover, and we collected samples of litter and soil. The carbon pool of trees and shrubs was calculated using allometric equations, and for roots, litter, and soil, using the carbon content analysed in a laboratory or obtained from the literature. Carbon pools were analysed separately for three independent variables: plot type (Quercus/Pinus), tree basal area and slope. Overall, Quercus forests stored more carbon than Pinus plantations, thanks to a larger carbon stock in roots and shrubs in the former, which compensated for the larger aboveground carbon stock in tree biomass of Pinus plots. The carbon stock increased with basal area in all compartments except the soil. The carbon allocation pattern across compartments greatly varied between the two forest types, Pinus plots storing more than half (55%) of its carbon in the aboveground biomass of trees, while Quercus storing more carbon belowground (60%) in roots and soil. Given that belowground carbon stock is more resistant against disturbances, we conclude that native Quercus forests are more suitable for a long-term carbon storage.