Transcript Salix pulchra - Wageningen UR

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
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).
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
is used to reconstruct the growth
response to climate
B1 Cryptogram, herb barren
G1 Rush/Grass, forb, Cryptogram tundra
B2 Cryptogram barren compex (bedrock)
is used to reconstruct
the vegetation
response to climate
change on a large
spatial scale
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
Salix pulchra is a widespread
deciduous shrub across the Arctic
2,0
Greenness (NDVI) trends per Arctic vegetation class
NDVI regression trend slope
(0,001 NDVI unit year -1)
1,5
80
70
60
50
-0,5
-1,0
-1,5
B1
B2
B3
B4
P1
P2 G1 G2 G3 G4 S1
S2 W1 W2 W3 N1
40
Barren
30
20
1965
1975
1985
1995
2005
1,4
0,8
0,75
1,2
0,7
1,1
1,0
0,65
0,9
0,6
NDVI July Kytalyk
1,3
0,8
0,55
0,7
0,6
0,5
1986
1991
1996
2001
2006
Shrub growth can be tracked by
landscape-scale remote sensing
greenness data
(Pearson correlation = 0,39; P < 0,05)
16
1,6
14
1,4
12
1,2
10
1
8
0,8
6
0,6
4
0,4
2
0
1945
0,2
1955
1965
1975
1985
1995
Salix pulchra ring width residuals
0,85
Summer temperature (Celcius)
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.
1,5
Shrub
Wetland
Stongest positive greening trends occur in shrubdominated tundra areas
Salix pulchra cross section with raw ring-width measurements
0,9
0,8
0,7
0,6
R² = 0,50
0,5
0,4
0,3
0
20
40
60
80
Shrub cover (Betula nana) fractional cover estimate (%)
100
Active layer thickness (cm)
1955
Graminoid
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.
10
1945
Salix pulchra ring width residuals
0,0
-2,0
0
1981
0,5
NDVI
Salix pulchra ring width (0,01 mm)
90
1,0
50
Ridge 2007
Former lakebed 2008
40
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.
Ridge 2008
30
20
10
0
2005
Salix pulchra shrub growth is closely
related to summer temperature from
mid June to mid July (Pearson
correlation = 0,73; P < 0,001)
Former lakebed 2007
0
20
40
60
80
100
Deciduous shrub (Betula nana) fractional cover (%)
Spectral reflection data show positive
correlation between shrub cover and
greenness on a landscape scale
(Pearson correlation = 0,71; p < 0,01)
Permafrost thaw is negatively
correlated with deciduous shrub
cover (r2 = 0,80; P < 0,01)
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
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