Changes in soil organic matter associated with afforestation affect erosion processes: The case of erodible volcanic soils from Patagonia

•Pinus afforestation on coarse-textured volcanic soils increases labile organic matter fractions.•Soil aggregation and the formation of stable microaggregates are enhanced in the afforested soils.•Changes in soils depend on initial organic matter contents and afforestation age.•Erosion processes in afforestation involve the removal of microaggregates rich in organic matter and silt fractions.•In plantations, total soil losses due to erosion processes are low but sediments are highly enriched with organic matter.