Collaborative Research: 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, & Caroline Lewis

What is ITEX?• International Network of experiments• Focus on climate change impacts on tundra vegetation of Arctic and

Alpine (recently Antarctic)• Formalized 1990, earliest sites initiated 1992• Primary experiment: passive warming (1-2 ºC) with Open Top

Chambers (OTCs), non-destructive measurements.

• Networking (16 workshops)• Standard protocols (ITEX manual)• Outputs

– Phenology (synth. workshop 1996, publ. 1997, 1999)– Community (synth. workshop 2001, publ. 2005, 2006– Ecosystem (synth. publ. 2007)

ITEX sites directly and collaboratively involved with this project (Southern Australian and Switzerland sites not shown).

1 Thule, Greenland2 Barrow, Alaska3 Atqasuk, Alaska4 Toolik, Alaska5 Tibetan Plateau, China6 Niwot Ridge, Colorado

Project components• Phenological Change (weekly, 2007, 2008)

– Compare control vs. warmed, current vs. past– Remeasurement of first green leaf, flowering & seed set and progression of growth

& reproductive effort• Community Change (once peak season, 2007 or 08 )

– Compare control vs. warmed, current vs. past – Remeasurement of ITEX plots and km2 grids at Toolik & Imnavait Creek using point

framing• Ecosystem change (once peak season, 2007 or 08 )

– Compare control vs. warmed – Reflectance measurements of cover/biomass (NDVI) and photosynthetic physiology

(PRI)– Leaf, litter, and soil nutrients– Leaf and litter isotopes (13C, 15N, 18O)– Leaf secondary compounds (tannins and lignins)– Radiocarbon of soil respiration (age of carbon leaving soil)

Synthesis workshops

• Phenological change 2008

• Community change 2009

Data management• Data collection: all non real-time• Limited sites-weekly: plant phenology,

plot reflectance• Cross sites-peak season: reflectance; point-quadrat

plot canopy structure and composition; nutrients and isotopes of leaves, litter, and soil; leaf tannins and lignins; respiratory and soil radiocarbon

• Data Screening: Data double checked/ outlier/visualization screening

• Metadata: JOSS format• Data archiving: NSIDC

Major results

• 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

The value of ITEX for IPY

• Stable network, broad international coverage

• Long-term data 10-15 years for some.– Experimental changes– Changes on Controls– Detailed vegetation analysis– Ecosystem – Nondestructive (repeated measures)