Plant Responses to Temperature in Barrow and Atqasuk, Alaska
Robert T Slider and Dr. Robert D. Hollister
Grand Valley State University
30
Results & Discussion
Differences between mean date of first flower burst in control and experimental treatments varied by species (Figure 2). For instance: In the Barrow
Dry site, the species Cassiope tetragona consistently flowered significantly earlier in warmed plots than in controls while Luzula arctica did not display a
consistent trend (Figure 2). Flowering trends in control plots at Barrow also followed a consistent trend of earlier flowering with higher mean July temperature
(Figure 3) Differences between average maximum inflorescence lengths in each treatment also varied by species (Figure 4). While the general response of
tundra vegetation to warming has been shown to be an increase in reproductive effort and earlier flowering, findings have also shown that response to
warming varies from species to species (Arft et al. 1999, Hollister et al. 2005). This is shown in the inflorescence heights at the Atqasuk Dry Site (Figure 4)
where there are multiple examples of inflorescences in experimental plots that are shorter that those in controls.
Analysis of relationships between mean July temperature and each developmental trait yielded r2 values varying from 0.03 to 0.75 (Figure 5). 50% of
the r2 values obtained were categorized as medium while 7% were strong, and 43% were weak. This wide range of strengths suggests that while
temperature significantly influences the development of some species, others are influenced more by other factors. r2 values were generally higher in Barrow
than in Atqasuk. This may be explained by the fact that Barrow is typically colder, and therefore Barrow plants would likely show a greater response to a heat
source. Because mean July temperature does not account for the timing of snowmelt or heat experienced by the plants during the entire growing season,
these trends may appear weaker or stronger than they actually are. Further analysis using thawing degree days may prove useful in explaining trends seen
both in inflorescence height and date of flower burst.
Atqasuk
70°29’N
157°25’W
25
20
15
10
5
0
1996
230
1997
1998
1999
2000
2007
2008
Year
Conclusion
Some significant differences were seen in reproductive timing and inflorescence growth between plants in control and OTC plots. Findings supported
those of previous studies which showed a varied response to warming by species (Arft et al. 1999, Hollister et al. 2005). Evidence was found that some trends
seen in artificial warming experiments, such as an increase in inflorescence length and earlier flower burst, are evident in annula temperature variation.
240
Barrow
35
Length of Inflorescence (cm)
Introduction
Under a changing climate the Arctic is expected to
experience the greatest amount of warming of any ecoregion on
earth (IPCC 2007). Because Arctic plants are adapted to thrive in
cold temperatures their responses to warming is of interest to
those seeking to predict the impacts of climate change.
Numerous studies have shown, in general, that arctic plants
respond to artificial warming with increased inflorescence length,
and earlier flower burst (Arft et al. 1999, Hollister et al. 2005). By
examining the responses of plants to artificial and natural
temperature variations, this study seeks to find whether
responses seen under artificial warming are also evident in
annual temperature variation. This topic is becoming of
increasing interest to those studying the effects of climate change
on tundra vegetation as it may provide valuable insight into the
rates of expected responses under a warming climate.
Barrow 71°18’N
156°40’W
Diapensia lapponica
Minuartia obtusiloba
Luzula arctica
Polygonum bistorta
Carex Bigelowii
Luzula confusa
Control
Warmed
Hierachloe alpina
Figure 4: Average maximum inflorescence length at the Atqasuk Dry site by treatment
and year. Error bars represent the standard error of the mean.
Barrow Wet
25
200
190
180
170
25
20
20
Inflorescence height (cm)
WET
Atqasuk
Barrow Dry
210
Inflorescence height (cm)
DRY
First Flower Burst (Julian Days)
220
15
10
160
15
10
5
5
150
1995
1996
1997
1998
1999
2000
2007
2008
0
3.5
Year
Salix rotundifolia
Luzula arctica
Cassiope tetragona
Stellaria laeta
Control
Potentilla hyparctica
Luzula confusa
Saxifraga punctata
Papaver hultenii
Warmed
Barrow Dry
Barrow Wet
240
220
210
200
190
180
170
160
150
3.5
220
r2 =
4.5
Salix rotundifolia,
0.01
Potentilla hyparctica r2 = 0.61
Stellaria laeta, r2 = 0.68
5
5.5
6
Mean July Temperature (ºC)
Luzula arctica, r2 = 0.01
Luzula confusa, r2 = 0.53
Papaver hultenii, r2 = 0.69
6.5
7
Cassiope tetragona, r2 = 0.51
Saxifraga punctata, r2 = 0.35
6
6.5
0
3.5
7
Saxifrage punctata, r2 = 0.45
Luzula arctica, r2 = 0.27
Luzula confusa, r2 = 0.53
Potentilla hyparctica, r2 = 0.74
Papaver hultenii, r2 = 0.38
Arctagrostis latifolia, r2 = 0.15
210
200
190
180
170
4
4.5
Saxifraga cernua, r2 = 0.48
5
5.5
6
Mean July Temperature (ºC)
Luzula arctica, r2 = 0.48
6.5
7
Eriophorum russeolum, r2 = 0.24
Eriophorum triste, r2 = 0.08
Luzula confusa, r2 = 0.14
Saxifraga hieracifolia, r2 = 0.44
Carex stans, r2 = 0.18
Dupontia fisheri, r2 = 0.45
Hierachloe pauciflora, r2 = 0.34
Poa arctica, r2 = 0.41
Aqasuk Dry
Aqasuk Wet
30
30
25
25
20
15
10
20
15
10
5
0
0
7
8
9
10
11
12
13
7
8
Carex bigelowii, r2 = 0.12
Minuatia obtusiloba, r2 = 0.03
Luzula confusa,
r2 =
0.67
9
10
11
12
13
Mean July Temperature (ºC)
Mean July Temperature (ºC)
Diapensia lapponica, r2 = 0.15
Polygonum bistorta, r2 = 0.51
Hierachloe alpina,
r2 =
0.65
Pedicularis sudetica, r2 = 0.42
Carex rariflora, r2 = 0.04
Eriophorum angustifolium, r2 = 0.45
Eriophorum russeolum, r2 = 0.75
Carex aquatilis, r2 = 0.17
Dupontia psilosantha, r2 = 0.38
Luzula arctica, r2 = 0.03
Figure 5: Average maximum inflorescence height in control plots compared to mean July temperatures.
Bibliography
Arft, A.M., M.D. Walker, J. Gurevitch, J.M. Alatalo, M.S. Bret-Harte, M. Dale, M. Diemer, F. Gugerli, G.H.R. Henry, M.H. Jones, R.D. Hollister, I.S. Jónsdóttir, K. Laine, E. Lévesque, G.M. Marion, U. Molau, P. Mølgaard,
U. Nordenhäll, V. Raszhivin, C.H. Robinson, G. Starr, A. Stenström, M. Stenström, ø. Totland, P.L. Turner, L.J. Walker, P.J. Webber, J.M. Welker, and P.A. Wookey. 1999. Response patterns of tundra plant
species to experimental warming: a meta-analysis of the International Tundra Experiment. Ecological Monographs 69(4): 491-511.
160
150
4
5.5
5
230
Inflorescence height (cm)
Mean First Flower Burst (Julian Days)
First Flower Burst (Julian Days)
230
5
Poa arctica, r2 = 0.45
Inflorescence height (cm)
Methods
Research was conducted at four sites in Barrow and Atqasuk, Alaska (Figure 1). Sites represented dry heath and wet meadow plant communities and are thus termed Barrow Dry, Barrow Wet, Atqasuk Dry, and
Atqasuk Wet. Each site contains 24 control plots and 24 warmed plots. Open Top Chambers (OTC’s) were used to warm tundra vegetation during the summer growing season (Mid-June through the end of August). OTC’s act
similarly to green houses by letting light pass through, but trapping infrared radiation. On average these chambers warm the plots by 2ºC (Hollister, R.D., P.J. Webber 2000).
Growth of marked specimens was measured once each week and phenological developments were observed twice each week. Temperature at canopy height (13cm) was collected at 15 minute intervals by probes
attached to Campbell Data Loggers. Temperatures were averaged and stored every hour for the duration of the year.
The maximum inflorescence length of marked individuals, and largest reproductive specimens, was averaged by plot and then by treatment at each site. Treatments were compared to examine differences in
inflorescence lengths due to warming. Inflorescence lengths in control plots were compared to the mean July temperature, an estimation of heat energy experienced during the growing season, to investigate responses to
natural temperature variation and compare these with responses to artificial warming. First date of flower burst was averaged by treatment type and compared to mean July temperature to examine responses to warming and
natural temperature variation. Significant differences in inflorescence height and flower burst between warmed and control treatments were described as those beyond the standard error of the mean. r2 values were found for
correlations between both developmental characteristics and mean July temperature. r2 values of less than 0.35 were considered weak, 0.35-0.70 were considered medium, and greater than 0.70 were considered strong.
4.5
Mean July Temperature (ºC)
Figure 2: Average date of first flower burst by year and treatment. Error bars represent
the standard error of the mean.
Figure 1: Location and scheme of Study sites in Barrow and Atqasuk, Alaska.
4
Height of Inflorescence (cm)
1994
3.5
4
4.5
5
5.5
6
6.5
7
Mean July Temperature (ºC)
Luzula arctica, r2 = 0.24
Saxifraga hieracifolia, r2 = 0.63
Draba lactea, r2 = 0.48
Carex stans, r2 = 0.62
Figure 3: Average date of first flower burst in control plots compared to mean July temperatures.
Hierachloe pauciflora, r2 = 0.77
Dupontia fisheri, r2 = 0.49
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. 230 pp.
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.
Hollister, R.D. and P.J. Webber 2000. Biotic validation of small open-top chambers in a tundra ecosystem. Global Change Biology 6(7): 835-842.