Increasing deciduous shrub abundance in the Arctic could alter the biotic and abiotic controls on carbon (C) cycling in these ecosystems. Betula glandulosa (Michx.) leaf litter was decomposed at three sites of differing shrub abundance in the Canadian Low Arctic for one year. Summer and winter microclimate along with soil nutrients were monitored and lab incubations simulated autumn temperatures and leaching conditions. At the high shrub site, warmer winter soil temperatures contrasted with cooler summer temperatures likely due to deeper snow and greater thickness of moss and organic soil layers compared to the other sites. However, surface mass loss was significantly higher at the shrubbier site only after a full year suggesting that microclimate was not the only influencing factor. At all sites, large mass losses (21-26%) occurred between August and May with no significant differences among sites. The laboratory study suggested that much of the mass loss occurred shortly after litterfall in autumn.iii