Long-Term Response of Luzula arctica and Luzula confusa to
Warming in the Alaskan Tundra
Kelseyann Kremers and Dr. Robert Hollister
Results
Introduction
Atqasuk
Figure 2 (Left): Location of study sites at
Barrow and Atqasuk, Alaska
Inflorescence Height
For L. confusa, TDD is a significantly better predictor of growth
and reproduction than Julian day. This is not the case for L.
arctica. Increased temperature (TDD) results in taller
inflorescences and longer leaves for both species. L. confusa
produces longer leaves in Atqasuk, whereas L. arctica generally
produces longer leaves in Barrow. In Barrow, both species
generally show a positive response to the warming treatment for
both leaf length and inflorescence height, while there is no
consistent trend in Atqasuk. There is not an obvious trend with
increasing years of treatment.
Discussion
Inflorescence Length
Atqasuk control
Barrow control
R2=.347
T
25
Atqasuk warmed
Barrow warmed
20
15
15
10
10
5
5
0
0
160
170
16
14
12
10
8
6
4
2
0
180
190
200
210
230
R2=.447
J
160
220
170
180
190
200
210
220
0
16
14
12
10
8
6
4
2
0
230
100 200 300 400 500 600 700 800
R2=.590
J
0
2007
2008
R2=.854
T
25
20
1998
1999
2000
R2=.543
T
10
8
8
6
6
4
4
2
2
0
0
160
Figure 3 (Below): Open-top chamber used
to warm experimental plots
170
180
190
200
210
3
230
R2=.695
J
3.5
220
0
3
2.5
2
2
1.5
1.5
1
1
0.5
0.5
0
0
160
170
180
190
200
Julian Day
210
220
230
100 200 300 400 500 600 700 800
R2=.301
J
3.5
2.5
R2=.916
T
10
0
The results show that each species has an individualistic response
to warming, which supports previous findings (Chapin and Shaver
1985, Hollister et al. 2005). Also, species may differ in which
factors largely control growth and reproductive response. While
temperature seems to be a primary factor controlling growth for
L. confusa, it seems to be subordinate to other factors for L.
arctica. Changes in these non-temperature factors may slow the
rate of vegetation change caused by temperature, and the
magnitude of variation in these other factors in relation to the
affects of warming will determine the amount of delay. (Hollister
et al. 2005). Furthermore, large fluctuations in these other
factors may exclude the changes caused by warming (Hollister et
al. 2005). Therefore, predicting the response of vegetation due to
climate warming is difficult because of the relationship between
temperature and non-temperature factors, and also because
each species shows a unique response.
100 200 300 400 500 600 700 800
Leaf Length
Luzula arctica
Leaf Length (cm)
Barrow
Figure 4: Growth
measurement diagram
Figure 1: : Photographs of L. arctica (A) and L. confusa (B)
taken at Barrow, Alaska in summer 2010
Luzula arctica
Luzula confusa
Inflorescence Height (cm) Inflorescence Height (cm)
Sites were established at Barrow (71°18’N, 156° 44’W) in 1994
and Atqasuk (70°29’N, 157°25’W) in 1996 (Figure 2). Atqasuk is
located about 60 miles south of Barrow and is further inland.
Both experience arctic climates, but average temperatures in
Atqasuk are generally 4°C warmer than Barrow in the summer.
Plots of vegetation (1m2) were warmed 1°C to 3°C using open-top
fiberglass chambers (Figure 3). Each dry site contains 24 warmed
plots and 24 control plots. Growth measurements (Figure 4) of L.
confusa and L. arctica were collected from mid June to late
August in each control and warmed plot containing the species
(the species were not found in all plots at each site).
B
Luzula confusa
Leaf Length (cm)
Methods
A
Leaf Length
Higher latitudes are expected to show the earliest and greatest
response to global climate change. Air temperature has been
increasing in the arctic at much faster rates than the rest of the
globe (IPCC 2007). Low temperatures limit the growth and
reproduction of arctic plants, so an increase in temperature could
greatly affect the community. Changes in community structure
or composition of arctic plants could influence the productivity of
the ecosystem. The International Tundra Experiment (ITEX) uses
experimental warming to study how tundra plants respond to
increased temperature. In general, previous studies have shown
that arctic plants respond to warming with increased growth and
reproductive effort (Hollister et al 2005). This study focuses on
two closely related species, Luzula arctica (Figure 1A) and Luzula
confusa (Figure 1B). The objective of this study was to determine
if the response to warming is similar or unique for each species,
and also to see if temperature is a good predictor of plant growth
and reproductive response. Thawing degree days (TDD), which
integrate time and temperature, were used to represent
temperature for comparisons across sites, treatments, and years.
100 200 300 400 500 600 700 800
TDD
Figure 5: Graphs of growth measurement (inflorescence height or leaf length) vs. Julian day or
TDD. Graphs denoted “T” show a trait that is better predicted by TDD than Julian day. Graphs
denoted “J” show a trait that does not show a substantial improvement in prediction when
represented by TDD. R2 values were calculated using the square of the growth measurement.
Acknowledgements:
Thank you to the National Science Foundation (NSF) for funding, Barrow Arctic
Science Consortium (BASC) for logistic support, and our colleagues with the
International Tundra Experiment (ITEX) for insight and guidance. Also, thank
you to GVSU Arctic Ecology Program members Jenny Leibig, Jeremy May, and
Robert Slider for your help and support.
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
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.
Chapin, F. S., III, and G.R. Shaver. 1985. Individualistic growth response of
tundra plant species to environmental manipulations in the field.
Ecology 66: 564-576.