Barren Graminoid Shrub Wetland

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B1 B2 B3 B4 P1 P2 G1 G2 G3 G4 S1 S2 W1 W2 W3 N1

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Greenness (NDVI) trends per Arctic vegetation class

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 tundraDaan 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

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, 1296-1305Walker 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)

DendrochronologySalix 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

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1945 1955 1965 1975 1985 1995 2005

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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 (r2 = 0,80; P < 0,01)

Dendrochronology Remote Sensing

R² = 0,50

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Shrub cover (Betula nana) fractional cover estimate (%)0,5

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1981 1986 1991 1996 2001 2006

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Deciduous shrub (Betula nana) fractional cover (%)

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) Former lakebed 2007

Ridge 2007

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Ridge 2008

Dendrochronology and Remote sensing are combined to scale up response to local climate conditions from the individual shrub level to pan-Arctic vegetation trends.

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1945 1955 1965 1975 1985 1995 2005

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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.

ConclusionIncreased 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.