Heating the tundra: Experimental warming results from the International Tundra Experiment (ITEX)

The International Tundra Experiment (ITEX) was established in the early 1990’s to examine the effects of predicted warming on tundra ecosystems.  Standardized experimental designs and measurements at ITEX sites have allowed powerful syntheses of results.  The simple passive warming devices used in ITEX warm the tundra by 1-3 °C during the growing season. In this presentation, I will review the results of three syntheses conducted at the species, plant community and ecosystem scales.  Short-term growth and reproductive responses of individual species could not be used to accurately predict the plant community changes.  Results at the individual plant scale indicated that the tundra would become more herbaceous. However, plant community measurements showed a general increase in cover and biomass of woody plants in ITEX warming experiments.  This confirmed the role of climate warming in observations of increased shrub cover in low Arctic areas over the past few decades.  Warming increased both ecosystem respiration and gross photosynthesis and the balance (net ecosystem exchange) depended on initial soil moisture conditions and showed annual variation.  In general, the sink strength was reduced in wet tundra and dry tundra tended to change from a source to a small sink.  Implications of these results and future plans will also be presented.