Vegetation Shift in the Pan-Arctic Tilmann Silber & Daniel Angst Topics 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 balance alteration of carbon balance change in hydrology Topics in Ecosystem Ecology FS > 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 (T s ) Topics in Ecosystem Ecology FS20093

Remote Sensing AVHRR Sensors on NOAA Satellites Normalized Difference Vegetation Index NDVI = (a NIR – a V )/(a NIR + a V ) T s : Land surface temperature Topics in Ecosystem Ecology FS20094 NOAA HRPT –

Theoretical Framework Topics in Ecosystem Ecology FS20095 hydric Regime radiative Regime Ecotone

Results / Conclusion Topics in Ecosystem Ecology FS20096

Tape et al Goal: upscale evidence for shrub expansion to pan-Arctic level Combining three lines of evidence: – Repeated photography in Alaska: ca – 2001 – Review of plot studies & NDVI studies Topics in Ecosystem Ecology FS2009

Repeated Photography Detection of shrubs > 0.5 m Covers predominantly river valleys Topics in Ecosystem Ecology FS2009

Results photography Topics in Ecosystem Ecology FS2009 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 Topics in Ecosystem Ecology FS2009

Critical: interpreting NDVI values Higher shrub coverage! Longer growing season!  Authors: Both Topics in Ecosystem Ecology FS2009

Can it be upscaled? Yes: Alaska Canada Uncertain (?): Scandinavia Sibiria  To be discussed! Topics in Ecosystem Ecology FS2009

When did it start? Application of a logistic growth model to the data Calculation of starting point: ca – 1925 (very rough) Literature: current warming in Alaska started about 1970  Little Ice Age? (Last minimum ~ 1850; cooling less than 1°C) Topics 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? Topics in Ecosystem Ecology FS2009

References Fillol, E.J. & Royer, A., 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, July, pp Tape, K., M. Sturm and C. Racine, The evidence for shrub expansion in Northern Alaska and the Pan-Arctic. Global Change Biol., 12(4): Topics in Ecosystem Ecology FS200915

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