BarrenGraminoidShrub Wetland B1 Cryptogram, herb barren G1 Rush/Grass, forb, Cryptogram tundra B2 Cryptogram barren compex (bedrock) P1 Prostrate dwarf-shrub, herb tundra G2 Graminoid, prostrate dwarf-shrub, herb tundra P2 Prostrate/Hemiprostrate dwarf-shrub tundra G3 Nontussock sedge, dwarf shrub, moss tundra G4 Tussock-sedge, dwarf-shrub, moss tundra S1 Erect dwarf-shrub tundra S2 Low-shrub tundra W1 Sedge/grass, moss wetland W2 Sedge, moss, dwarf-shrub wetland W3 Sedge, moss, low-shrub wetland B3 Noncarbonate mountain complex B4 Carbonate mountain complex N1 Nunatuk complex Climate change effects on vegetation in Northeastern Siberian tundra Daan Blok 1, Ute Sass-Klaassen 2, Gabriela Schaepman-Strub 3, Harm Bartholomeus 4, Monique Heijmans 1, Frank Berendse 1 1 Nature Conservation & Plant Ecology, Wageningen University, NL; 2 Forest Ecology and Forest Management, Wageningen University, NL; 3 Institute for Evolutionary Biology and Environmental Studies, University of Zurich, CH; 4 Centre for Geo-Information, Wageningen University, NL o The Siberian tundra is a key permafrost region in the Arctic because of its large spatial extent and carbon-rich soils. o Permafrost thaw can have large impacts on the global climate and is believed to strongly increase this century. o Arctic deciduous shrubs are predicted to respond to climate warming by extending their cover. o Experiments show that increase in deciduous shrub cover reduces summer permafrost thaw (Blok et al., 2010). Spectral reflection data show positive correlation between shrub cover and greenness on a landscape scale (Pearson correlation = 0,71; p < 0,01) Email: Daan.Blok@wur.nl References : Blok et al, 2010. Shrub expansion may reduce permafrost thaw, Global Change Biology,16, 1296-1305 Walker et al, 2005. The Circumpolar Arctic Vegetation Map, Journal of Vegetation Science, 16 (3): 267-282 Salix pulchra shrub growth is closely related to summer temperature from mid June to mid July (Pearson correlation = 0,73; P < 0,001) Dendrochronology Salix pulchra shrub growth correlates positively with summer temperature and tundra greenness (NDVI), suggesting that (further) increase in arctic shrub cover can be expected with climate warming. is used to reconstruct the growth response to climate Salix pulchra is a widespread deciduous shrub across the Arctic Salix pulchra cross section with raw ring-width measurements is used to reconstruct the vegetation response to climate change on a large spatial scale Shrub growth can be tracked by landscape-scale remote sensing greenness data (Pearson correlation = 0,39; P < 0,05) Stongest positive greening trends occur in shrub- dominated tundra areas Greening trends are based on early July 15-day average NDVI values from the GIMMS AVHRR dataset (Nov. 2008), with a spatial resolution of 8 km. Regression slopes are calculated per pixel, as a function of NDVI change per year over the entire available record period 1981-2006. Arctic vegetation class map: Walker et al, 2005. Permafrost thaw is negatively correlated with deciduous shrub cover (r 2 = 0,80; P < 0,01) Dendrochronology Remote Sensing Dendrochronology and Remote sensing are combined to scale up response to local climate conditions from the individual shrub level to pan-Arctic vegetation trends. A ring-width chronology for Salix pulchra is calculated from 19 individuals. For each shrub, an average of measured ring widths at multiple heights in each shrub is used. Remote sensing Ground-based spectral reflectance measurements show that NDVI increases with deciduous shrub cover on landscape scale. Summer permafrost thaw is reduced by an increase in deciduous shrub cover. Conclusion Increased shrub growth on local scale will enhance shrub cover on landscape scale which leads to reduction in permafrost thawing and hence will effect climate on global scale.