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

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 coverageLong-term data 14-17 years for some.

Experimental changesChanges on ControlsDetailed vegetation analysisEcosystem Nondestructive (repeated measures)

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, km2 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 (13C, 15N, 18O)– 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

YEAR2007200119951989

Mea

n n

um

ber

of

hit

s/p

lot

24

22

20

18

16

14

12

102007200119951989

ERIVAG

BETNAN

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

Vascular plants

Lichens

Bryophytes

Dead vascular plants

Leaf Litter

Control

Warmed

Lea

f ar

ea in

dex

Imnavait Creek

Depth

(cm

) Radiocarbon can differentiate old versus new carbon(Collaboration with Ted Schuur University of Florida)

25

20

15

10

5

0

-200 -100 0 100 200 300 400 500

14C (‰)

D. Schell, unpublished

-300

-200

-100

0

100

200

300

Recentdetritus

Plantrespiration

Oldsoil C

14C

(‰

)-300

-250

-200

-150

-100

-50

0

50

100

150

200

ToolikkdryCTRLatnjadryCTRToolikmoistCTRBarrowwetCTRAtqasukwetCTRLatnjamoistCTR

Delta 14CO

2

Control

OTC warmedExtensive ThawModerate ThawMinimal Thaw

Growing Season SumOld C Respiration

(g C m-2)

010203040506070

010203040506070

2004 2005 2006