vegetation shift in the pan-arctic tilmann silber & daniel angst 2.3.20091topics in ecosystem...
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Vegetation Shift in the Pan-Arctic
Tilmann Silber & Daniel Angst
2.3.2009 1Topics in Ecosystem Ecology FS2009
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?
2.3.2009 14Topics in Ecosystem Ecology FS2009
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!