1. Study of Arctic ecosystem changes in the IPY using the International Tundra Experiment (ITEX). Steve Oberbauer, Robert Hollister, Jeff Welker, Julia Klein, William Gould, Patrick Sullivan, Bartmar Sveinbjornsson, Keith Boggs, and Caroline Lewis

2. What is ITEX? International Network of experiments Focus on climate change impacts on tundra and alpine vegetation initiated 1992. Passive warming (1-2 ºC) with Open Top Chambers (OTCS), non-destructive measurements. OTC approach validated with natural climate variation Phenology changes with small temperature increase Controls are changing with background Community changes toward taller, shrubbier with warming Wet sites accumulate carbon, dry sites release carbon with warming Stable network, broad international coverage Long-term data 14-17 years for some. Experimental changes Changes on Controls Detailed vegetation analysis Ecosystem Nondestructive (repeated measures)

3. Project components Phenological Change (weekly, 2007, 2008) across network –Remeasurement of control vs. warmed –Compare current vs. current, current vs. past Community Change (once peak season, 2007 or 08 ) –Remeasurement of ITEX control vs. warmed, km 2 grids at Toolik and Imnavait Creek. –Compare current vs. current, current vs. past Ecosystem change (once peak season, 2007 or 08 ) –Compare long-term control vs. warmed –Reflectance measurements of cover/biomass (NDVI) and photosynthetic physiology (PRI) –Leaf, litter, and soil nutrients –Leaf and litter isotopes ( 13 C, 15 N, 18 O) –Leaf secondary compounds (tannins and lignins) –Radiocarbon of soil respiration (age of carbon leaving soil) Synthesis workshops (phenology 2008, community 2009) –With Canadian IPY, CEON, Back to the Future, Greening of Arctic

4. YEAR 2007200119951989 Mean number of hits/plot 24 22 20 18 16 14 12 10 2007200119951989 ERIVAG BETNAN Vascular plants Lichens Bryophytes Dead vascular plants Leaf Litter Control Warmed Leaf area index Imnavait Creek

5. Depth (cm) Radiocarbon can differentiate old versus new carbon (Collaboration with Ted Schuur University of Florida) -300 -200 -100 0 100 200 300 Recent detritus Plant respiration Old soil C  14 C (‰) Extensive Thaw Moderate Thaw Minimal Thaw Growing Season Sum Old C Respiration (g C m -2 ) 0 10 20 30 40 50 60 70 0 10 20 30 40 50 60 70 20042005 2006