The Arctic is extremely Vulnerable to projected climate change. and global warming may result in major community reorganizations. The aim of this study was it thorough investigation of plant biomass production throughout a entire growing season in five different high arctic vegetation types: Cassiope, Dryas, and Salix heath, grassland. and fell. The main focus was on the gross ecosystem production (GEP), and the biotic and abiotic factors which may influence GEP. Photosynthesis, aboveground biomass, and carbon, nitrogen, and chlorophyll content were measured weekly during nine weeks. There were large differences in seasonal growth and production within and among vegetation types. Mosses contributed considerably to the total C and N pool in grassland, fen, and Salix heath. Fell, which had the highest pool of leaf N, leaf chlorophyll. and moss N, was the most productive vegetation type in terms of GEP, despite the lowest total biomass. Across vegetation types. leaf biomass, leaf N, and moss N pool size influenced GEP. Within most vegetation types GEP correlated with leaf N, in correspondence with the notion that N may limit plant production in many high arctic ecosystems. The timing of the peaks in C and N pools in leaves did not coincide with that in the mosses and in woody tissues. This emphasizes the importance of sampling throughout the growing season, when using Field data from the Arctic to estimate plant biomasses and modeling C and N fluxes and pool sizes.