Long-Term Response of Luzula arctica and Luzula confusa to Warming in the Alaskan Tundra

• Expected to show earliest and greatest response to global climate change (IPCC 2007)

Why Arctic?• Linked to global climate (ACIA 2004)

Study Sites

Barrow71°18’N, 156°40’W

Atqasuk70°29’N, 157°25’W

Experimental Design

2 Dry Heath Communities:Atqasuk DryBarrow Dry

1 Meter squared plots-24 Control-24 Warmed

Passive open-top fiberglass chambersIncrease temperature 1-3° C

Luzula arctica and Luzula confusa

•Common rushes at both dry heath sites•Associated with disturbances•Known to hybridize

MeasurementsSummer 1994-2010

- Inflorescence Height- Number of Inflorescences- Flowering date

L. arcticaHulten (1968)

Inflorescence Height

Inflorescence Height

1994 1995 1996 1997 1998 1999 2000 2001 2007 2008 20105

7

9

11

13

15

17

19

Luzula confusaBarrow ControlBarrow WarmedAtqasuk ControlAtqasuk Warmed

Year

Mea

n In

flore

scen

ce H

eigh

t (cm

)

Inflorescence Height

1995 1996 1998 1999 2000 2001 2007 2008 20105

6

7

8

9

10

11

12

13

14 Luzula arctica Barrow ControlBarrow WarmedAtqasuk ControlAtqasuk Warmed

Year

Mea

n In

flore

scen

ce H

eigh

t (cm

)

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)

1 2 3 4 5 6 7 8 9 10 11 12 13 14-2

0

2

4

6

8

10

12

14

16

18

20

22

-2

0

2

4

6

8

10

12

14

16

18

20

22

Thaw

ing

Degr

ee D

ays (

TDD)

Average Tem

perature (°C)

Julian Day

Thawing Degree Days (TDD)

1 2 3 4 5 6 7 8 9 10 11 12 13 14-2

0

2

4

6

8

10

12

14

16

18

20

22

-2

0

2

4

6

8

10

12

14

16

18

20

22

Thaw

ing

Degr

ee D

ays (

TDD)

Average Tem

perature (°C)

Julian Day

Inflorescence Height

1994 1995 1996 1997 1998 1999 2000 2001 2007 2008 20105

7

9

11

13

15

17

19

Luzula confusaBarrow ControlBarrow WarmedAtqasuk ControlAtqasuk Warmed

Year

Mea

n In

flore

scen

ce H

eigh

t (cm

)

Inflorescence Height

1994 1995 1996 1997 1998 1999 2000 2001 2007 2008 20105

7

9

11

13

15

17

19

Luzula confusaBarrow ControlBarrow WarmedAtqasuk ControlAtqasuk Warmed

Year

Mea

n In

flore

scen

ce H

eigh

t (cm

)

Inflorescence HeightLuzula confusa

200 300 400 500 600 700 800 9004

5

6

7

8

9

10

11

12

13

14

1995

2001

2008

2000

1997

1999

20101996

1994

1998

2007

TDD

Mea

n In

flore

scen

ce H

eigh

t (cm

)

Inflorescence HeightLuzula confusa

200 300 400 500 600 700 800 9004

6

8

10

12

14

16

18

20

22

R² = 0.743810696225732

TDD

Mea

n In

flore

scen

ce H

eigh

t (cm

)

Inflorescence HeightLuzula confusa

200 300 400 500 600 700 800 9004

6

8

10

12

14

16

18

20

22

R² = 0.266641242436093

R² = 0.269084055216121

R² = 0.192558814636371R² = 0.221979190962307

Barrow ControlLinear (Barrow Control)Barrow WarmedLinear (Barrow Warmed)Atqasuk ControlLinear (Atqasuk Control)

TDD

Mea

n In

flore

scen

ce H

eigh

t (cm

)

Inflorescence HeightLuzula arctica

200 300 400 500 600 700 800 9004

6

8

10

12

14

16

R² = 0.456356848798255

TDD

Mea

n In

flore

scen

ce H

eigh

t (cm

)

Inflorescence HeightLuzula arctica

200 300 400 500 600 700 800 9004

5

6

7

8

9

10

11

12

13

14

R² = 0.00180208421119543

R² = 0.118477442452011

R² = 0.00119242424381139

R² = 0.16112259246933

Barrow ControlLinear (Barrow Control)Barrow WarmedLinear (Barrow Warmed)Atqasuk ControlLinear (Atqasuk Control)

TDD

Mea

n In

flore

scen

ce H

eigh

t (cm

)

No change in warmed plots

Increase in height with increasing TDD in control plots

SummaryLuzula confusa

Inflorescence HeightOverall: Increased TDD is associated with increased height.All sites/treatments show no trend.

Luzula arcticaInflorescence Height

Overall: Increased TDD is associated with increased height.All sites/treatments suggest increased height with increased TDD.

Number of Inflorescences Luzula confusa

200 300 400 500 600 700 800 9000

5

10

15

20

25

R² = 0.00252100841425573

TDD

Mea

n N

umbe

r of I

nflor

esce

nces

/ m

2

Number of Inflorescences Luzula confusa

200 300 400 500 600 700 800 9000

2

4

6

8

10

12

14

R² = 0.346205366980748

R² = 0.0286850390842689

R² = 0.233643131615076R² = 0.158360992060014 Barrow ControlLinear (Barrow Control)Barrow WarmedLinear (Barrow Warmed)Atqasuk Control

TDD

Mea

n N

umbe

r of I

nflor

esce

nces

/ m

2

Fewer inflorescences in warmed plots at both sites

Number of Inflorescences Luzula arctica

200 300 400 500 600 700 800 9000

1

2

3

4

5

6

7

8

9

R² = 0.249528646110344

TDD

Mea

n N

umbe

r of I

nflor

esce

nces

/ m

2

Number of Inflorescences Luzula arctica

200 300 400 500 600 700 800 9000

1

2

3

4

5

6

7

8

9

R² = 0.0992700491964593R² = 2.11575476335435E-05

R² = 0.0138006350531638

R² = 0.00174840102028595

Barrow ControlLinear (Barrow Control)Barrow WarmedLinear (Barrow Warmed)Atqasuk ControlLinear (Atqasuk Control)

TDD

Mea

n N

umbe

r of I

nflor

esce

nces

/ m

2

No significant change

SummaryLuzula confusa

Inflorescence HeightOverall: Increased TDD is associated with increased height.All sites/treatments show no trend.

Luzula arcticaInflorescence Height

Overall: Increased TDD is associated with increased height.All sites/treatments suggest increased height with increased TDD.

Number of InflorescencesOverall: No trend.Control plots had more inflorescences than warmed plots.

Number of InflorescencesOverall: increased TDD is associated with decreased number of inflorescences.All sites/treatments show no trend.

Flowering DateLuzula confusa

1993 1996 1999 2002 2005 2008 2011155

160

165

170

175

180

185

190

195

200

205

R² = 0.0518577330391073R² = 0.0444774403931488

R² = 0.0669776656504306

R² = 0.0511030942947056

Barrow ControlLinear (Barrow Control)Barrow WarmedLinear (Barrow Warmed)Atqasuk ControlLinear (Atqasuk Control)

Year

Mea

n Fl

ower

ing

Date

(Jul

ian

Day) Earlier flowering date in

warmed plots

Flowering is earlier in Atqasuk

Flowering DateLuzula arctica

1993 1996 1999 2002 2005 2008 2011160

165

170

175

180

185

190

195

200

205

R² = 0.0215260845044534R² = 0.130054963917021

R² = 0.0840363165219424R² = 0.0549255803926146

Barrow ControlLinear (Barrow Control)Barrow WarmedLinear (Barrow Warmed)Atqasuk ControlLinear (Atqasuk Control)Atqasuk Warmed

Year

Mea

n Fl

ower

ing

Date

(Jul

ian

Day)

Flowering is earlier in Atqasuk

SummaryLuzula confusa

Inflorescence HeightOverall: Increased TDD is associated with increased height.All sites/treatments show no trend.

Luzula arcticaInflorescence Height

Overall: Increased TDD is associated with increased height.All sites/treatments suggest increased height with increased TDD.

Number of InflorescencesOverall: No trend.Control plots had more inflorescences than warmed plots.

Number of InflorescencesOverall: increased TDD is associated with decreased number of inflorescences.All sites/treatments show no significant change.

Flowering DateFlowering occurs earlier with warming.

Flowering DateNo 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 FoundationGVSU Arctic Ecology ProgramJeremy May, Robert Slider, Jennifer LiebigBarrow 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.