Coniferous afforestation increases soil carbon in maritime sand dunes

Abstract

Afforestation of grasslands can increase C sequestration and provide additional economic and environmental benefits. Pine plantations, however, have often been found to deplete soil organic C and trigger detrimental effects on soils. We examined soil characteristics under a 45-year-old Pinus radiata stand and under adjacent grassland on maritime dunes in temperate Argentina. Soil under the pine plantation had greater soil organic C (+93%), total N (+55%) and available P (+100%) concentrations than under grassland. Carbon was stored under the pinestand at an estimated mean accretion rate of 0.64 Mg ha−1 y−1. At 0- to 25-cm depth, soil C amounted to 61 Mg ha−1 under pine and 27 Mg ha−1 under grassland. Soil C accumulated more on dune slopes (35 Mg ha−1 y−1) than on ridges(29 Mg ha−1 y−1) and bottoms (12 Mg ha−1 y−1). Compared with the grassland, soil acidity, cation-exchange capacity, base losses (K > Ca = Mg) and C/N ratio increased under pine. Spatial heterogeneity in soil characteristics was greater under pine than under grassland. Such variability was non-systematic and did not support the ‘single-tree influence circle’ concept. Afforestation increased C in soil, forest floor and tree biomass in dunes with ustic climate regime.