Change in soil carbon after land clearing or afforestation in highly weathered lateritic and sandy soils of south-western Australia

Soil organic carbon (SOC) is a significant component of the worlds terrestrial carbon stocks, and changes in land-use have potential to change pools of soil C. Land-use change is occurring over large areas of the world, so soil has potential to be a large source or sink for atmospheric C. Changes in amounts of soil C (0-1 m) were examined after clearing of native vegetation for pasture (20-71 years prior to study), and after establishment of Eucalyptus globulus plantations on ex-pasture sites (7-10 years prior to study). A suite of 10 sites in south western Australia were used in a three-way comparison between native vegetation, pasture and plantation. Soil types across the 10 sites included Acrisols, Arenosols, and a Ferrosol. Soil C was measured in the fine earth (<2 mm), the 2-5 mm soil fraction, in charcoal and roots retained on a 5 mm screen, and in surface litter. Differences in soil bulk density between land-uses were accounted for by calculating depths for equivalent weights of soil. Despite large increases in soil fertility with conversion to pasture, amounts of soil C changed little. The amount of C in the 5-20 cm increment was significantly greater under pasture than native vegetation (mean of 8.4 Mg ha-1, <5 mm), but in surface soil (0-5 cm) and <20 cm, there were no significant differences in soil C content between land-uses. Less C in soil at 5-20 cm under native vegetation was offset by significantly more C in coarse roots (average of 5 Mg ha-1 higher to 1 m depth), surface soil (2-5 mm fraction, 2 Mg ha-1), and in standing pools of surface litter (9.8 Mg ha-1). Amounts of soil C under plantation were not significantly different from pasture 7-10 years after plantation establishment. However, plantation soils had an average of 3.1 Mg ha-1 more C in coarse roots than pasture, and significant quantities of C in surface litter (average of 7.9 Mg ha-1). Overall, soil C content in the sites of this study was relatively stable and the effect of land-use change was limited.