Vegetation Shift in the Pan-Arctic

Tilmann Silber & Daniel Angst

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Introduction

Climate Warming: 2°C per decade for the last 30 years in the Arctic

Evidence for shift in land surface vegetation on a local scale.

alteration of surface energy balancealteration of carbon balancechange in hydrology

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-> also on a larger scale?

Fillol & Royer, 2003

monitoring of ecotone Taiga/Tundra movement in Canada with remote sensing data

Data Basis: NDVI, Surface Temperature (Ts)

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Remote Sensing

AVHRR Sensors on NOAA Satellites

Normalized Difference Vegetation IndexNDVI = (aNIR – aV)/(aNIR + aV)

Ts: Land surface temperature

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NOAA HRPT – 28.7.2008 http://www.wetter-welt.de/

Theoretical Framework

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hydric Regimeradiative Regime

Ecotone

Results / Conclusion

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Tape et al. 2006

• Goal: upscale evidence for shrub expansion to pan-Arctic level

• Combining three lines of evidence:– Repeated photography in Alaska: ca. 1949 – 2001– Review of plot studies & NDVI studies

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Repeated Photography

Detection of shrubs > 0.5 m

Covers predominantly river valleys

1949

2001

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Results photography

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Disturbances!

Plot & NDVI studies

• Plot studies– Consistent trend for increase in shrub coverage – Covers shrubs < 0.5m

• NDVI studies: consistently increasing values in Alaska and the Arctic

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Critical: interpreting NDVI values

Higher shrub coverage!

Longer growing season!

Authors: Both2.3.2009 11Topics in Ecosystem Ecology FS2009

Can it be upscaled?Yes:

•Alaska

•Canada

Uncertain (?):

•Scandinavia

•Sibiria

To be discussed!

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When did it start?Application of a logistic growth model to the data

Calculation of starting point: ca. 1875 – 1925 (very rough)Literature: current warming in Alaska started about 1970

Little Ice Age? (Last minimum ~ 1850; cooling less than 1°C)2.3.2009 13Topics in Ecosystem Ecology FS2009

Discussion

• Consistent shift in both studies• What fraction of change is accountable to

recent warming? (ecologic equilibrium?)• High shrub expansion in valleys due to

nutrients?• Data hardly quantifyable how to assess the

effects of shrub expansion at global scale?

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References

Fillol, E.J. & Royer, A., 2003. Variability analysis of the transitory climate regime as defined by the NDVI/Ts relationship derived from NOAA-AVHRR over Canada. In: Proceedings 2003 IEEE International, Geoscience and Remote Sensing Symposium, IGARSS '03, 21-25 July, pp. 2863-2865.

Tape, K., M. Sturm and C. Racine, 2006. The evidence for shrub expansion in Northern Alaska and the Pan-Arctic. Global Change Biol., 12(4): 686-702.

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Thank you!