Long-Term Response of Luzula arctica and Luzula confusa
to Warming in the Alaskan Tundra
Why Arctic?
••Linked
Expected
to global
to show
climate
earliest
(ACIA
and2004)
greatest response to global
climate change (IPCC 2007)
Study Sites
Experimental Design
2 Dry Heath Communities:
Atqasuk Dry
Barrow Dry
Barrow
71°18’N, 156°40’W
Atqasuk
70°29’N, 157°25’W
1 Meter squared plots
-24 Control
-24 Warmed
Passive open-top fiberglass chambers
Increase temperature 1-3° C
Luzula arctica and Luzula confusa
•Common rushes at both dry heath sites
•Associated with disturbances
•Known to hybridize
Measurements
Inflorescence Height
Summer 1994-2010
- Inflorescence Height
- Number of Inflorescences
- Flowering date
L. arctica
Hulten (1968)
Inflorescence Height
Luzula confusa
Atqasuk Warmed
19
Mean Inflorescence Height (cm)
Barrow Control
Barrow Warmed
Atqasuk Control
17
15
13
11
9
7
5
1994
1995
1996
1997
1998
1999
Year
2000
2001
2007
2008
2010
Inflorescence Height
Mean Inflorescence Height (cm)
14
Luzula arctica
Barrow Control
Barrow Warmed
Atqasuk Control
13
Atqasuk Warmed
12
11
10
9
8
7
6
5
1995
1996
1998
1999
2000
Year
2001
2007
2008
2010
Question:
• What factor is causing a negative
response in these years?
Relate to temperature:
Thawing Degree Days (TDD)- cumulative
degree days above freezing (0°C)
Thawing Degree Days (TDD)
22
20
20
18
18
Thawing Degree Days (TDD)
22
16
14
14
12
12
10
10
8
8
6
6
4
4
2
2
0
0
-2
1
2
3
4
5
6
7
8
Julian Day
9
10
11
12
13
14
Average Temperature (°C)
16
-2
Thawing Degree Days (TDD)
22
20
20
18
18
Thawing Degree Days (TDD)
22
16
14
14
12
12
10
10
8
8
6
6
4
4
2
2
0
0
-2
1
2
3
4
5
6
7
8
Julian Day
9
10
11
12
13
14
Average Temperature (°C)
16
-2
Inflorescence Height
Luzula confusa
Atqasuk Warmed
19
Mean Inflorescence Height (cm)
Barrow Control
Barrow Warmed
Atqasuk Control
17
15
13
11
9
7
5
1994
1995
1996
1997
1998
1999
Year
2000
2001
2007
2008
2010
Inflorescence Height
Luzula confusa
Atqasuk Warmed
19
Mean Inflorescence Height (cm)
Barrow Control
Barrow Warmed
Atqasuk Control
17
15
13
11
9
7
5
1994
1995
1996
1997
1998
1999
Year
2000
2001
2007
2008
2010
Inflorescence Height
Luzula confusa
20
Mean Inflorescence Height (cm)
18
16
14
2007
1999
2008
12
1998
2000
10
1996
2010
2001
1995
8
1997
1994
6
4
200
300
400
500
TDD 600
700
800
900
Inflorescence Height
Luzula confusa
22
Mean Inflorescence Height (cm)
20
18
16
R² = 0.74
P<.05
14
12
10
8
6
4
200
300
400
500
600
TDD
700
800
900
Inflorescence Height
Luzula confusa
22
Mean Inflorescence Height (cm)
20
18
16
14
12
Barrow Control
R² = 0.22
Barrow Warmed
10
R² = 0.19
Atqasuk Control
8
R² = 0.27
Atqasuk Warmed
6
R² = 0.27
4
200
300
400
500
TDD
600
700
800
900
Inflorescence Height
Mean Inflorescence Height (cm)
16
Luzula arctica
14
12
10
R² = 0.4564
P<.05
8
6
4
200
300
400
500
TDD
600
700
800
900
Inflorescence Height
Luzula arctica
16
Barrow Control
R² = 0.16
Barrow Warmed
R² <.01
Mean Inflorescence Height (cm)
Atqasuk Control
14
Increase in height
with increasing TDD in
control plots
12
R² = 0.12
Atqasuk Warmed
R² <.01
10
8
No change in warmed
plots
6
4
200
300
400
500
TDD
600
700
800
900
Summary
Luzula confusa
Luzula arctica
Inflorescence Height
Overall: Increased TDD is
associated with increased height.
All sites/treatments suggest
increased height with increased
TDD.
Inflorescence Height
Overall: Increased TDD is
associated with increased height.
All sites/treatments show no trend.
Number of Inflorescences
Luzula confusa
Mean Number of Inflorescences / m2
25
20
R² <.01
15
10
5
0
200
300
400
500
TDD
600
700
800
900
Number of Inflorescences
25
Luzula confusa
Barrow Control
R² = 0.16
Mean Number of Inflorescences / m2
Barrow Warmed
R² = 0.23
Atqasuk Control
20
R² = 0.03
Atqasuk
WarmedR² = 0.35
Fewer inflorescences in
warmed plots at both sites
15
10
5
0
200
300
400
500
TDD
600
700
800
900
Number of Inflorescences
Luzula arctica
9
Mean Number of Inflorescences / m2
8
7
R² = 0.2495
P<.05
6
5
4
3
2
1
0
200
300
400
500
TDD
600
700
800
900
Number of Inflorescences
Luzula arctica
9
Barrow Control
Mean Number of Inflorescences / m2
R² = 0.01
Barrow Warmed
8
R² <.01
Atqasuk Control
7
R² <.01
Atqasuk Warmed
R² = 0.10
6
No significant change
5
4
3
2
1
0
200
300
400
500
600
TDD
700
800
900
Summary
Luzula confusa
Luzula arctica
Inflorescence Height
Inflorescence Height
Overall: Increased TDD is associated
with increased height.
All sites/treatments suggest
increased height with increased TDD.
Number of Inflorescences
Overall: No trend.
Control plots had more
inflorescences than warmed plots.
Overall: Increased TDD is
associated with increased height.
All sites/treatments show no trend.
Number of Inflorescences
Overall: increased TDD is
associated with decreased number
of inflorescences.
All sites/treatments show no
trend.
Flowering Date
Luzula confusa
205
Barrow Control
R² = 0.05
Barrow Warmed
Mean Flowering Date (Julian Day)
R² = 0.07
Atqasuk Control
200
R² = 0.04
Earlier flowering date in
warmed plots
195
Atqasuk
WarmedR² = 0.05
190
185
180
Flowering is earlier in
Atqasuk
175
170
1993
1996
1999
2002
Year
2005
2008
2011
Flowering Date
Luzula arctica
205
Barrow Control
R² = 0.05
Barrow Warmed
R² = 0.08
Mean Flowering Date (Julian Day)
200
Atqasuk Control
R² = 0.13
195
Atqasuk Warmed
R² = 0.02
190
185
180
175
170
Flowering is earlier in
Atqasuk
165
160
1993
1996
1999
Year
2002
2005
2008
2011
Summary
Luzula confusa
Luzula arctica
Inflorescence Height
Inflorescence Height
Overall: Increased TDD is associated
with increased height.
All sites/treatments suggest
increased height with increased TDD.
Number of Inflorescences
Overall: No trend.
Control plots had more
inflorescences than warmed plots.
Flowering Date
Flowering occurs earlier with
warming.
Overall: Increased TDD is
associated with increased height.
All sites/treatments show no trend.
Number of Inflorescences
Overall: increased TDD is
associated with decreased number
of inflorescences.
All sites/treatments show no
significant change.
Flowering Date
No significant change.
Conclusions
• Both species are responding to warming
• Each species responds differently
• Response is different for each site
Future Plans
• Continue to look at other relationships.
– What other factors are involved?
• More phenology
Questions?
Acknowledgements:
National Science Foundation
GVSU Arctic Ecology Program
Jeremy May, Robert Slider, Jennifer Liebig
Barrow Arctic Science Consortium
References:
IPCC (ed) 2007. Climate Change 2007: The Scientific Basis. Contribution of Working Group II to
the Third Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge
University Press. Cambridge, United Kingdom. pp. 230
ACIA 2004. Impacts of a Warming Arctic: Arctic Climate Impact Assessment. Cambridge
University Press. Cambridge, United Kingdom.
Hollister, R.D., P.J. Webber, and C. Bay. 2005. Plant response to temperature in northern Alaska:
Implications for predicting vegetation change. Ecology. 86(6): 1562-1570.