AbstractRecently, there have been several studies using open top chambers (OTCs) or cloches to examine the response of Arctic plant communities to artificially elevated temperatures. Few, however, have investigated multitrophic systems, or the effects of both temperature and vertebrate grazing treatments on invertebrates. This study investigated trophic interactions between an herbivorous insect (Sitobion calvulum, Aphididae), a woody perennial host plant (Salix polaris) and a selective vertebrate grazer (barnacle geese,Branta leucopsis). In a factorial experiment, the responses of the insect and its host to elevated temperatures using open top chambers (OTCs) and to three levels of goose grazing pressure were assessed over two summer growing seasons (2004 and 2005).OTCs significantly enhanced the leaf phenology ofSalixin both years and there was a significantOTCby goose presence interaction in 2004.Salixleaf number was unaffected by treatments in both years, butOTCs increased leaf size and mass in 2005.Salixreproduction and the phenology of flowers were unaffected by both treatments. Aphid densities were increased byOTCs but unaffected by goose presence in both years. While goose presence had little effect on aphid density or host plant phenology in this system, theOTCeffects provide interesting insights into the possibility of phenological synchrony disruption. The advanced phenology ofSalixeffectively lengthens the growing season for the plant, but despite a close association with leaf maturity, the population dynamics of the aphid appeared to lack a similar phenological response, except for the increased population observed.