Retention trees slow post-harvest fine-root decomposition in a coastal temperate rainforest

•Fine-root decomposition was measured under variable retention and clearcut harvests.•Fine-root decomposition was 15–19% slower under retention trees vs in a clearcut.•Faster in open decomposition did not persist as stands regenerated.•Fine-root biomass, and NO3−, K+, and SO42− availability predicted fine root C loss.•Retention forestry may reduce soil C losses following harvest.