TUNDRA PLANTS AND CLIMATE-CHANGE - THE INTERNATIONAL TUNDRA EXPERIMENT (ITEX)

The International Tundra Experiment (ITEX) was established in late 199 0 at a meeting of arctic tundra ecologists as a response to prediction s that the human-enhanced greenhouse warming would occur earliest and most intensely at high latitudes. The initial objective of ITEX was to monitor phenology, growth and reproduction in major circumpolar vascu lar plant species in response to climate variations and environmental manipulations at sites throughout the tundra biome. The manipulations involve passive warming of tundra plots in open-top chambers (OTCs), a nd manipulating snow depth to alter growing season length. Standard pr otocols were developed for measurements, experimental design and stati stical analyses, and published in an ITEX Manual. The standard methods ensure comparable data are collected at all sites. This special issue of Global Change Biology is based on papers developed from the 6th IT EX Workshop, held at the University of Ottawa, Ottawa, Canada, 7-11 Ap ril 1995. The papers compare shortterm responses (1-3 years) of common species to climate variations and manipulations at ITEX sites. The OT Cs increase mean near-surface temperatures by 1-3 degrees C during the growing season, simulating predictions from global circulation models . All species investigated responded to the temperature increase, espe cially in phenology and reproductive variables. However, these short-t erm responses were individualistic, and no general pattern in type or magnitude of response was noted for functional types or phenology clas s. Responses were generally similar among sites, although the magnitud e of response tended to be greater in high Arctic sites. Early snowmel t increased carbon:nutrient ratios in plants. Sustained growth and rep roductive responses to warming will depend on nutrient supply, and inc reased carbon:nutrient ratios in litter could buffer nutrient cycling, and hence plant growth. Ongoing, long-term research at ITEX sites, li nked to other global change initiatives, will help elucidate probable effects of climate change at the ecosystems level in arctic and alpine tundra.