Barren

1. Climate change effects on vegetation in Northeastern Siberian tundra Daan Blok1, Ute Sass-Klaassen2, Gabriela Schaepman-Strub3, Harm Bartholomeus4, Monique Heijmans1, Frank Berendse1 1Nature Conservation & Plant Ecology, Wageningen University, NL; 2Forest Ecology and Forest Management, Wageningen University, NL; 3Institute for Evolutionary Biology and Environmental Studies, University of Zurich, CH; 4Centre for Geo-Information, Wageningen University, NL • The Siberian tundra is a key permafrost region in the Arctic because of its large spatial extent and carbon-rich soils. • Permafrost thaw can have large impacts on the global climate and is believed to strongly increase this century. • Arctic deciduous shrubs are predicted to respond to climate warming by extending their cover. • Experiments show that increase in deciduous shrub cover reduces summer permafrost thaw (Blok et al., 2010). Dendrochronology and Remote sensing are combined to scale up response to local climate conditions from the individual shrub level to pan-Arctic vegetation trends. Dendrochronology Remote Sensing 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 is used to reconstruct the growth response to climate is used to reconstruct the vegetation response to climate change on a large spatial scale Salix pulchra is a widespread deciduous shrub across the Arctic Barren Graminoid Shrub Wetland 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. Stongest positive greening trends occur in shrub-dominated tundra areas Salix pulchra cross sectionwith raw ring-width measurements 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. Spectral reflection data show positive correlation between shrub cover and greenness on a landscape scale (Pearson correlation = 0,71; p < 0,01) Shrub growth can be tracked by landscape-scale remote sensing greenness data (Pearson correlation = 0,39; P < 0,05) Salix pulchra shrub growth is closely related to summer temperature from mid June to mid July (Pearson correlation = 0,73; P < 0,001) Permafrost thaw is negatively correlated with deciduous shrub cover (r2 = 0,80; P < 0,01) 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. 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. • 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 Email: Daan.Blok@wur.nl