Dominant tree species and earthworms affect soil aggregation and carbon content along a soil degradation gradient in an agricultural landscape

•Small macroaggregates and microaggregates higher under Zanthoxylum gilletii trees.•Soil aggregate-C decreased by almost 40% with increasing duration of cultivation.•The magnitude of soil C loss was dependent on the tree species.•C loss is likely enhanced by activity of earthworm species Nematogenia lacuum.