Production and nutrient dynamics of plant communities on a sub-antarctic island

Summary Investigations of the seasonal changes in vegetation standing crop have enabled an assessment of annual net primary production (ANP) at a fjaeldmark, open fernbrake and closed fernbrake at Marion Island (46°54S, 37°45E). These communities represent a successional sequence on relatively dry ridges and slopes on the island. Together, they are representative of a large proportion of the island's lowland (c. 300 m above sea level) vegetation. Aboveground ANP's were 728 g m^-2 y^-1 at closed fernbrake, 502 g m^-2 y^-1 at open fernbrake and 226 g m^-2 y^-1 at fjaeldmark. Total (above-plus below) ANP's were 1958 g m^-2 y^-1, 1578 g m^-2 y^-1 and 685 g m^-2 y^-1, respectively. These values are greater than those found for most tundra and tundra-like shrub and dwarf shrub-dominated communities of the northern hemisphere. The island's oceanic climate ensures a long growing season (c. 300 days for vascular plants, 365 days for bryophytes) and aboveground productivities for the island communities (including two mire-grasslands reported on previously), based on the length of the growing season, were 0.9 to 2.9 g m^-2 d^-1, lower than for most comparable shrub and dwarf shrub sub-Arctic or alpine communities and more similar to low Artic and low alpine sedge-moss and grass-herb communities. Production efficiencies (0.7% to 2.1% of photosynthetically active radiation) were in the range reported for northern hemisphere subpolar vegetations.