Impact of unusually wet permafrost soil on understory vegetation and CO2 exchange in a larch forest in eastern Siberia

•Unusual perennial excess soil water enhanced growth of understory vegetation of larch forest.•Through wet years and following drying years understory GPP and ER increased, while no trend was found in ecosystem fluxes.•Declined overstory larch led to preferable light condition and enhanced turbulent mixing for understory fluxes.•The understory growth and remaining deeper soil water compensated for the declined larch contribution to all ecosystem fluxes.