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Studies of the growth of arctic willow (Salix arctica) and arctic bell-heather (Cassiope tetragona) in the High Arctic

Northern Worlds
– landscapes, interactions and dynamics
Research at the National Museum of Denmark
Proceedings of the Northern Worlds Conference
Copenhagen 28-30 November 2012
Edited by
Hans Christian Gulløv
Publications from the National Museum
Studies in Archaeology & History Vol. 22
Copenhagen 2014
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Publications from the National Museum
Northern Worlds – landscapes, interactions and dynamics
Research at the National Museum of Denmark
Proceedings of the Northern Worlds Conference
Copenhagen 28-30 November 2012
© e National Museum of Denmark and the authors, 2014
All rights reserved
Edited by Hans Christian Gulløv
Technical edition: Marie Lenander Petersen
Linguistic revision and translation: David Young
Cover design and layout by Donald Geisler Jensen
Set with Adobe Garamond Pro and Univers
Printed in Denmark by Narayana Press, Gylling
Published by University Press of Southern Denmark
Campusvej 55, DK-5230 Odense M
ISBN: 978 87 7674 824 1
Cover photo: Rock carvings, Hjemmeluft, Alta, Finnmark, North Norway, photographer Ditlev L. Mahler, 2010
e proceedings are funded by e Augustinus Foundation
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98281_Nordlige verdener_004_r1.indd 1 23/09/14 08:57
Per Kristian Madsen
Preface 9
Hans Christian Gulløv
Introduction 11
I. Landscapes
Peter Emil Kaland
Heathlands – land-use, ecology and vegetation history as a source for archaeological interpretations 19
Use and traces
Ditlev Mahler
Shetland – the Border of Farming 4000-3000 BC 49
Alison Sheridan
Shetland, from the appearance of a ‘Neolithic’ way of life to c. 1500 BC: a view from the ‘mainland 67
Christian Koch Madsen
Norse Pastoral Farming and Settlement in the Vatnahver Peninsula, South Greenland 95
Cosmos and perception
Flemming Kaul
e northernmost rock carvings belonging to the Scandinavian Bronze Age tradition 115
Lars Jørgensen
Norse religion and ritual sites in Scandinavia in the 6th-11th century 129
Nordlige verdener Ombr 25.6.indd 5 14/08/14 09.33
Ulla Odgaard
Clash of Concepts – Hunting rights and ethics in Greenlandic caribou hunting 151
Environment and changes
Morten Fischer Mortensen, Peter Steen Henriksen, Charlie Christensen,
Peter Vang Petersen and Jesper Olsen
Late glacial and early Holocene vegetation development in southeast Denmark
– palaeoenvironmental studies from a small lake basin close to the Palaeolithic site of Hasselø 169
Kevin Edwards
Early farming, pollen and landscape impacts from northern Europe
to the North Atlantic: conundrums 189
Richard Oram
From ‘Golden Age’ to Depression: land use and environmental change
in the medieval Earldom of Orkney 203
Noémie Boulanger-Lapointe and Claudia Baittinger
Studies of the growth of arctic willow (Salix arctica)
and arctic bell-heather (Cassiope tetragona) in the High Arctic 215
II. InteractIons
Charlotte Damm
Interaction: When people meet 227
Networks and communication
Christina Folke Ax
Good connections – Networks in the whaling and sealing community on Rømø
in the 18th century 241
Einar Østmo
Shipbuilding and aristocratic splendour in the North, 2400 BC-1000 AD 257
Anne Lisbeth Schmidt
Skin Clothing from the North – new insights into the collections of the National Museum 273
Peter Andreas Toft
Small things forgotten – Inuit reception of European commodities in the Historic ule Culture 293
Objects and exchange
Anne Pedersen
Skagerrak and Kattegat in the Viking Age – borders and connecting links 307
Helle Winge Horsnæs
Appropriation and imitation – A Barbarian view on coins and imitations 319
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Gitte Tarnow Ingvardson
Trade and Power – Bornholm in the Late Viking Age 325
Lisbeth M. Imer
e tradition of writing in Norse Greenland – writing in an agrarian community 339
Maria Panum Baastrup
Continental and insular imports in Viking Age Denmark
– On transcultural competences, actor networks and high-cultural dierentiation 353
Preservation and decay
Martin Nordvig Mortensen, Inger Bojesen-Koefoed, David Gregory, Poul Jensen, Jan Bruun Jensen,
Anne le Boëdec Moesgaard, Nanna Bjerregaard Pedersen, Nataša Pokupčić, Kristiane Strætkvern and
Michelle Taube
Conservation and drying methods for archaeological materials modied for use in northern areas 369
Henning Matthiesen, Bo Elberling, Jørgen Hollesen, Jan Bruun Jensen and Jens Fog Jensen
Preservation of the permafrozen kitchen midden at Qajaa in West Greenland
under changing climate conditions 383
III. dynamIcs
Christian Wichmann Matthiessen and Richard D. Knowles
Scandinavian Links:
Mega Bridges/Tunnels Linking the Scandinavian Peninsula to the European Continent 395
Continuity and discontinuity
Bjarne Grønnow, Martin Appelt and Ulla Odgaard
In the Light of Blubber:
e Earliest Stone Lamps in Greenland and Beyond 403
Peter Steen Henriksen
Norse agriculture in Greenland – farming at the northern frontier 423
Mobility and organization
Einar Lund Jensen
Settlement policy in a colonial context – discussions on changing
the settlements structure in Greenland 1900-1950 433
Christopher Prescott
A synthesis of the history of third millennium north-western Scandinavia 449
Lasse Sørensen
Farmers on the move – e expansion of agrarian societies during
the Neolithic and Bronze Ages in Scandinavia 463
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Techniques and environment
Jens Fog Jensen and Tilo Krause
Second World War histories and archaeology in Northeast Greenland 491
Niels Bonde, Claudia Baittinger, omas Bartholin, Helge Paulsen and Frans-Arne Stylegar
Old Houses in Greenland – Standard Houses for Greenland. Dendrochronological studies 511
in timber houses
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215studies of the growth of arctic willow (salix arctica) and arctic bell-heather (cassiope tetragona)
(Serreze et al. 2000). Changes in winter and spring
precipitation have occurred due to a higher atmo-
spheric water vapour content and pole-ward vapour
transport (Kattenberg et al. 1996). Between 1950
and 1990, precipitation in Northern Canada in-
creased by as much as 20% (Groisman & Easterling
1994). Since this increase in precipitation primar-
ily occurred during winter, snow regimes are those
greatest aected. However, these changes have also
been accompanied by an overall decrease in snow
cover (Serreze et al. 2000). e area covered by snow
in early summer has fallen by 18% since 1966, in
response to earlier spring snow melt (AMAP 2011).
Late-lying and permanent snow patches are com-
mon features in the Arctic and are often the main
source of water for the richest and most productive
plant communities (Bliss & Matveyeva 1992). Ear-
lier snow melt, if not accompanied by an increase
in summer precipitation, will have a negative im-
pact on the vegetation. Similarly, rapid permafrost
thaw (Lawrence & Slater 2005) causes a lowering
of the soil water table (Hinzman et al. 2003) and
an increase in active layer depth, leading in some
areas to drainage of surface water. Cold permafrost
soils show poor decomposition and mineralisation.
Increased temperatures will enhance microbial ac-
tivity and thereby nutrient supply. Glaciers around
the Arctic have been melting at an increasingly rapid
rate in recent years (Kohler et al. 2007; Lemke et al.
Recent climate change is strongly aecting Arctic
regions where the recorded increase in air tem-
perature is twice the global average (ACIA 2004).
Northern ecosystems are fragile and generally less
resilient than those at lower latitudes. Environmen-
tal constraints push species to their physiological
limits (Billings 1987) and a short growing season
hinders rapid adaptation by limiting the time frame
available for reproduction and growth (Chapin
1983). e Arctic is often misleadingly depicted as
a homogenous entity. However, at the meter scale it
is probably one of the world’s most diverse ecosys-
tems; micro-habitats, created by very local moisture
supply and a variety of patterned-ground features,
form a mosaic of plant communities (Walker et al.
2011). At a regional scale, glacial history has played
a major role in the distribution and abundance of
plant species (Raynolds & Walker 2009). In order
to gain a better understanding of the impact of cur-
rent climate change on Arctic vegetation, this local
and regional diversity needs to be taken into ac-
During the last two to three centuries, average
global air and ocean temperatures have increased,
leading to cascading eects on global climate (IPCC
2007). In the Canadian Arctic, climate records show
an overall warming trend, dominated by increases in
winter temperatures in central and western regions
AND ARCTIC BELL-HEATHER (cassiope tetragona)
Noémie Boulanger-Lapointe and Claudia Baittinger
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landscapes – environment and changes noémie boulanger- lapointe and claudia baittinger
latitude (Arctic environments) (Myers-Smith et al.
2011). e transition towards greater shrub abun-
dance involves complex feedback mechanisms such
as changes in surface energy exchange and nutrient
availability. e tundra is subject to wind-drifting
eect, resulting in generally little snow accumula-
tion along topographic barriers and shrub patches
(Bewley et al. 2010). In winter, trapping of snow
insulates the soil leading to higher soil tempera-
tures, while in summer, shrub patches block solar
radiation and create a cooler micro-habitat (Myers-
Smith et al. 2011). Arctic soils consist of continu-
ous permafrost overlain by an active layer (Walsh
et al. 2005). e depth of the active layer oscillates
throughout the year, according to summer and win-
ter temperatures (Sturm et al. 2005). Shrub cover
inuences the depth of the active layer and the rate
of microbial activity within it. Moreover, shrubs
are generally darker in colour than the surrounding
tundra vegetation and therefore have a strong eect
2007). New areas are becoming available and plants
quickly colonize these favourable substrates (Breen
& Lévesque 2006).
An increase in shrub cover is expected to be one
of the major consequences of climate change for
Arctic terrestrial ecosystems. Although this phe-
nomenon has been documented in Low Arctic and
Alpine regions (e.g. Sturm et al. 2001; Forbes et al.
2010; Hallinger et al. 2010) limited information is
currently available for the prostrate woody species
of the High Arctic. For this region, covering nearly
20% of Arctic vegetated landscapes (Walker et al.
2005), predictions of plant community response to
climate change rely mainly on the results of remote
sensing (Bhatt et al. 2010) and experimental warm-
ing studies (Walker et al. 2006).
Current data show that in many regions shrubs
are growing at a faster rate, existing open patches
are becoming in-lled and the shrub line is moving
upwards in altitude (Alpine environments) and in
Fig. 1. Musk oxen in the Zackenberg valley. Photo Niels M. Schmidt.
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217studies of the growth of arc tic willow (salix arctica) and arctic bell-heather (cassiope tetragona)
portion of the musk ox diet is made up of willow
(Salix) species (Larter & Nagy 2004). Together
with mountain avens (Dryas octopetala L.), they are
the preferred food species of the collared lemming
(Berg 2003). Grazing by lemmings can be sucient
to aect vegetation productivity and depress NDVI
(Normalized Dierence Vegetation Index) values,
which reect vegetation density (Olofsson et al.
2012). However, the lemming population density
has been low recorded in the Zackenberg region
on the albedo, with a direct positive feedback to at-
mospheric heating.
Both large and small herbivores are known to
inhibit shrub growth and expansion through graz-
ing and trampling (Post & Pedersen 2008; Olofs-
son et al. 2009). e relative impact of herbivore
activity depends on species preference for a given
food source (Larter & Nagy 2004) and population
density (Olofsson et al. 2009; Speed et al. 2010). In
large parts of the High Arctic, the musk ox (Ovibos
moschatus Zimmermann) (g. 1) and the collared
lemming (Dicrostonyx groenlandicus Traill) account
for most of the grazing activity (Forchhammer et
al. 2008) and are, accordingly, likely to aect the
radial growth and other life-history traits of the
vegetation. Since High Arctic landscapes have low
plant productivity, herbivores may have a great
impact even at low density (Raillard & Svoboda
2000). Generally, but especially in winter, a large
Fig 2. Arctic willow (Salix arctica) on
an ablation plateau in the Zackenberg
valley. The plateau is snow-free for
most of the year; willow stems are
affected by wind abrasion and grazing
throughout the year.
Fig. 3. Arctic bell-heather (Cassiope tetragona)
Photo Noémie Boulanger-Lapointe.
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landscapes – environment and changes noémie boulanger- lapointe and claudia baittinger
At Zackenberg, arctic willows were collected
from four dierent plant communities, following
an altitudinal gradient: 1) a Salix snow-bed com-
munity (ca.15 m a.s.l.), largely dominated by arctic
willow and occurring on south-facing slopes with
late-lying snow patches; 2) an ablation plateau
(ca. 31 m a.s.l.), a barren community with little
snow cover and subject to a strong wind-drifting ef-
fect; 3) a Cassiope heath (ca.36 m a.s.l.) with an in-
termediate level of snow accumulation and ground
covered by small hummocks (Schmidt et al. 2010);
4) a fell-eld (ca.433 m a.s.l.), a barren commu-
nity with very little snow accumulation (Bay 1998).
Arctic bell-heather samples were only collected in
the Cassiope heath.
Study species
e arctic willow is a long-lived, deciduous and di-
oecious prostrate shrub. It has an ArcticAlpine dis-
tribution, is ubiquitous and stress-tolerant (Porsild
1957). In most habitats, it produces numerous and
densely-owered catkins (Argus et al. 1999) (g. 5).
Clonal growth contributes to species propagation
and is achieved through the formation of adventi-
tious roots on low branches (Argus et al. 1999). In
dense populations, branches intermingle, impeding
the recognition of single individuals. Nevertheless,
individuals established by seed (g. 6) can be distin-
since 2008, indicating a general low impact on the
vegetation (Jensen 2012).
In this study, we aimed to gain an understand-
ing of the growth patterns of two dominant shrub
species in the High Arctic, the arctic willow (Salix
arctica Pall.) (g. 2) and the arctic bell-heather (Cas-
siope tetragona (L.) D. Don) (g. 3). Field work was
conducted in Canada and Greenland between 2009
and 2011.
Study sites
e study was conducted in the Canadian Arctic Ar-
chipelago and on the northeast coast of Greenland
during July and August 2009 to 2011 (g. 4). Four
regions were studied, from south to north: Resolute,
Alexandra Fjord and Sverdrup Pass in Canada and
Zackenberg in Northeast Greenland. Arctic willow
growth was studied at all these sites, while arctic bell-
heather samples were only collected at Zackenberg.
At the Canadian sites, the studied areas all have low
vegetation cover, corresponding to the semi-desert
denition of Bliss & Matveyeva (1992) (vascular
plant cover 5%-20%), and are dominated by arctic
willow. e sites also t into bioclimatic subzones B
or C, dominated respectively by prostrate and hemi-
prostrate dwarf shrubs (Walker et al. 2005).
Fig. 4. Location of study sites in high
Arctic Canada and Greenland. The Arc-
tic bioclimatic subzones are defined on
the basis of a combination of summer
temperatures and vegetation. The map
modified from circumpolar Arctic veg-
etation region – bioclimate subzones
map (Walker et al. 2005).
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219studies of the growth of arctic willow (salix arctica) and arctic bell-heather (cassiope tetragona)
guished from clones by the characteristic form of their
main root. e dendrochronological potential of the
semi-ring porous annual rings of this shrub species
(Schwein gruber 1990) was recognised several years
ago (Beschel & Webb 1963; Raup 1963; Savile 1979;
Woodcock & Bradley 1994). However, cross-dating
diculties, due to a signicant number of missing or
incomplete rings, have limited ecological interpreta-
tions until recently (Schmidt et al. 2006, 2010).
e arctic bell-heather is a long-lived evergreen
shrub. Individuals reach 10-15 cm in height and
produce horizontal stems which branch extensively,
sometimes forming a continuous mat (Aiken et al.
2003). e species has been used since the 1990s
to develop a trans-Arctic chronology based on in-
ternode (Havstrom et al. 1993; Rayback & Henry
2005) and stem length (Rozema et al. 2009; Weijers
et al. 2010; Weijers et al. 2013). Arctic bell-heather
stem-length chronologies were derived from the dis-
tances between wintermarksepta, which are formed
at the end of the summer growth period when the
pith is narrowing (g. 8). Even though the species
Fig. 5. Arctic willow (Salix arctica) from Zackenberg valley.
Photograph of a female plant with almost mature seeds taken
on 20th July 2010. Photo Claudia Baittinger.
Fig. 6. Arctic willow (Salix arctica)
seedlings sorted by age class; a.
newly established, b. one year old, c.
two years old or more. Photo Noémie
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landscapes – environment and changes noémie boulanger- lapointe and claudia baittinger
during July and August 2009. At Zackenberg, be-
tween 10 and 30 arctic willows were collected from
the dierent community types mentioned above
during August 2010. A total of 24 arctic bell-heath-
er samples were collected from a Cassiope heath at
Zackenberg during August 2010 and 2011.
In order to assess their growth pattern, arctic
willow samples were boiled in water for 2 hours and
thin sections (15-20 µm) were made of the root col-
lar and one of the larger branches using a micro-
tome. e sections were then stained with a solu-
tion of 0.1% safranin, 0.1% alcian blue and 50%
ethanol, and subsequently mounted on slides using
a low viscosity mounting medium. When dried, the
sections were photographed using a camera mount-
ed on a binocular microscope (g. 7). Growth rings
were measured along at least two radii.
As mentioned above, arctic bell-heather stem
length chronologies were derived from the distances
between wintermarksepta. 12 individuals were cut
has numerous fragile branches, time series extend-
ing up to 169 years have been produced based on
samples from Svalbard (Weijers et al. 2010).
Sampling design and dendrochronological analysis
At the Canadian sites, 30 arctic willows were col-
lected in relatively homogenous semi-desert areas
Fig. 7. Cross-section of a Salix arctica stem. Stained and col-
our changed from red to blue in Adobe Photoshop.
Fig. 8. Drawing of arctic bell-heather (Cassiope tetragona).
The finely-branched individuals are very fragile. The leaves
are removed prior to preparation and, as a consequence,
only a few are seen on the drawing – at the very tips of the
branches. The scale applies to the whole plant, not to close-
ups A, B and C, which are shown at different magnifications.
A: Five wintermarksepta are visible within the pith of the stem
(arrowed) and thereby four complete years of shoot length
growth. Whereas dendrochronology is based on the width of
tree rings, here it is the length of the individual sections that is
measured. B: False wintermarkseptum (arrowed). These occur
most commonly at the end of long sections, i.e. at the close
of the growing season. Sometimes it is difficult to distinguish
them from true wintermarksepta, but the false examples are
often less distinct. C: Very short sections by a new branch
(arrowed). These are not included in the time series that rep-
resents the individual. Drawing Yvonne Schuster.
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221studies of the growth of arctic willow (salix arctica) and arctic bell-heather (cassiope tetragona)
has low availability of water, but also a long grow-
ing season due to the limited snow cover, and it is,
at least locally, rich in nutrients, resulting in high
annual radial growth. Consequently, although hav-
ing generally suboptimal conditions, the ablation
plateau may locally provide more favourable grow-
ing conditions than the Cassiope heath and the Salix
snow bed.
is study allowed us to obtain an overview of
arctic willow growth patterns throughout a range
of latitudes and environmental conditions (Bou-
langer-Lapointe et al. in press; Boulanger-Lapointe
e study also provided us with some of the rst
time-series based on arctic bell-heather growth in
Northeast Greenland. e samples of arctic bell-
heather are still being processed in the laboratory,
but preliminary results show that one of the 12 in-
dividuals collected in 2010 is at least 124 years old.
at means that the actual time-series derived from
wintermarksepta extends back to AD 1886.
In both these time-consuming techniques –
chronologies built up on the basis of shoot length
(arctic bell-heather) and growth rings (arctic wil-
low) – the goal is to achieve annual resolution in
the time-series produced, in order to obtain reliable
climate proxies. When working with the two dier-
ent species it became increasingly clear that there
are, despite the occurrence of false wintermarksepta
(g. 8), fewer irregularities in individuals of arctic
bell-heather than in stems and branches of arctic
willow. e likelihood of obtaining reliable data in
the form of time-series is therefore, from a dendro-
chronological point of view, greater when working
with arctic bell-heather – at least in the Zackenberg
With the help of a method called serial section-
ing, Buchwal et al. (2013) have shown that large
numbers of incomplete and missing rings occur in
polar willow (Salix polaris – has growth rings very
similar to arctic willow) from Svalbard. In the vari-
ous cross-sections, as many as every tenth growth
ring may be missing, and there is an even greater
number of incomplete rings. is makes it dicult
to work with individuals of this species. Only with
a high sample depth and many cross-sections per
individual (serial sectioning) is it possible to build
up a reliably site-chronology. Due to the very time
horizontally (g. 8) and annual shoot length growth
was measured on several branches with the aid of a
tree ring measuring station. For both species, cross
dating procedures were used to enhance the accu-
racy of age determination using the program TSAP-
preliminary results and discussion
e growth patterns seen in the dierent vegeta-
tion types indicate that the dry, barren conditions
of the semi-desert sites are more favourable for arc-
tic willow growth than richer, more vegetated ar-
eas. e arctic willow is a pioneer plant and shows
little tolerance to competition. On the other hand,
sites subject to grazing by large herbivores appear
to be less responsive to climatic conditions. Only
sheltered sites dominated by the arctic willow can
be seen to be responding positively to increasing
temperature, while a combination of winter and
summer precipitation was also important at the
other sites. Individuals from rich plant communi-
ties might therefore be rejected for future dendro-
climatological studies as they have too many narrow
and incomplete rings.
A previous study performed by Schmidt and
Forchhammer at Zackenberg showed that arctic
willow growth is linked both to musk ox population
density and to climate (Forchhammer et al. 2005).
Schmidt et al. (2006, 2010) also reported that radi-
al growth of arctic willow stems in the Zackenberg
valley was limited by the extent of spring snow cover
rather than temperature. e radial growth of arctic
willow in the Zackenberg valley shows marked year-
to-year uctuations, a pattern that can be attributed
to inter-annual variation in local snow fall. Large
accumulations of snow in spring delay the onset of
the growing season and contribute to limited an-
nual growth. Individuals of arctic willow exhibit a
consistent negative response to the amount of snow
fall, irrespective of gender and vegetation type.
In the Zackenberg valley, Schmidt et al. (2006,
2010) studied three of the four vegetation commu-
nities presented in this study (ablation plateau, Salix
snow bed, Cassiope heath). eir results show no dif-
ference in inter-annual growth pattern between the
communities, but vegetation type per se was impor-
tant for annual radial growth. e ablation plateau
Nordlige verdener Ombr 25.6.indd 221 14/08/14 09.48
landscapes – environment and changes noémie boulanger- lapointe and claudia baittinger
collected under permission of the Greenland Home
Rule. Special thanks to Christian Bay for his advice
and help in the eld, to Yvonne Schuster and Char-
lotte Kure Brandstrup for laboratory assistance, to
the Tree-Ring Laboratory at the University of Ho-
henheim for providing laboratory facilities and to
Stef Weijers for sharing his experience with respect
to sample taking and the preparation of arctic bell-
heather individuals.
ACIA. 2004. Arctic climate impact assessment: Impacts of
a warming Arctic. Cambridge University Press, Cam-
Aiken, S. G., Dallwitz, M. J., Consaul, L. L., McJannet, C. L.,
Gillespie, L. J., Boles, R. L., Argus, G. W., Gillett, J. M.,
Scott, P. J., Elven, R., LeBlanc, M. C., Brysting, A. K., &
Solstad, H. 2003. Flora of the Canadian Arctic Archipelago:
Descriptions, illustrations, identication, and information re-
trieval. Available from:
AMAP. 2011. Snow, water, ice and permafrost in the Arctic
(SWIPA): Climate change and the cryosphere. Oslo, Nor-
consuming method involved, it was not possible to
carry out serial sectioning on individuals of arctic
willow in this ongoing study.
However, in the future, we hope to be able to
complete a combined analysis of series of arctic wil-
low and arctic bell-heather samples collected in the
vicinity of each other in the Zackenberg valley.
is study was part of ‘e Northern Worlds’ proj-
ect of the National Museum of Denmark, mainly
funded by the private foundation, Augustinus Fon-
den. e work was made possible by nancial sup-
port of the Natural Sciences and Engineering Re-
search Council of Canada, the Fonds québécois de
la recherche sur la nature et les technologies, the
Northern Scientic Training Program, the Centre
d’études nordiques and ArcticNet. Logistical sup-
port for the eldwork at the research station at
Zackenberg (g. 9) was provided by the Depart-
ment of Bioscience, Aarhus University, and in Can-
ada by the Polar Continental Shelf Program and
the Royal Canadian Mounted Police. Samples were
Fig. 9. Late night volleyball-match at Zackenberg Research Station. Photo Claudia Baittinger on 29th July 2010 at 11:28 p.m.
Nordlige verdener Ombr 25.6.indd 222 17/09/14 10.40
223studies of the growth of arctic willow (salix arctica) and arctic bell-heather (cassiope tetragona)
tundra shrub willows. Global Change Biology 16: 1542-
Forchhammer, M. C., Post, E., Berg, T. B. G., Hoye, T. T. &
Schmidt, N. M. 2005. Local-scale and short-term herbi-
vore-plant spatial dynamics reect inuences of large-scale
climate. Ecology 86: 2644-2651.
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Full-text available
Measurements of snowmelt and turbulent heat fluxes were made during the snowmelt periods of two years at two neighbouring tundra sites in the Yukon, one in a sheltered location with tall shrubs exposed above deep snow and the other in an exposed location with dwarf shrubs covered by shallow snow. The snow was about twice as deep in the valley as on the plateau at the end of each winter and melted out about 10 days later. The site with buried vegetation showed a transition from air-to-surface heat transfers to surface-to-air heat transfers as bare ground became exposed during snowmelt, but there were daytime transfers of heat from the surface to the air at the site with exposed vegetation even while snow remained on the ground. A model calculating separate energy balances for snow and exposed vegetation, driven with meteorological data from the sites, is found to be able to reproduce these behaviours. Averaged over 30-day periods the model gives about 8 Wm<sup>−2</sup> more sensible heat flux to the atmosphere for the valley site than for the plateau site. Sensitivity of simulated fluxes to model parameters describing vegetation cover and density is investigated.
Full-text available
Question: What are the major vegetation units in the Arctic, what is their composition, and how are they distributed among major bioclimate subzones and countries? Location: The Arctic tundra region, north of the tree line. Methods: A photo-interpretive approach was used to delineate the vegetation onto an Advanced Very High Resolution Radiometer (AVHRR) base image. Mapping experts within nine Arctic regions prepared draft maps using geographic information technology (ArcInfo) of their portion of the Arctic, and these were later synthesized to make the final map. Area analysis of the map was done according to bioclimate subzones, and country. The integrated mapping procedures resulted in other maps of vegetation, topography, soils, landscapes, lake cover, substrate pH, and above-ground biomass. Results: The final map was published at 1:7 500 000 scale map. Within the Arctic (total area = 7.11 × 106 km2), about 5.05 × 106 km2 is vegetated. The remainder is ice covered. The map legend generally portrays the zonal vegetation within each map polygon. About 26% of the vegetated area is erect shrublands, 18% peaty graminoid tundras, 13% mountain complexes, 12% barrens, 11% mineral graminoid tundras, 11% prostrate-shrub tundras, and 7% wetlands. Canada has by far the most terrain in the High Arctic mostly associated with abundant barren types and prostrate dwarf-shrub tundra, whereas Russia has the largest area in the Low Arctic, predominantly low-shrub tundra. Conclusions: The CAVM is the first vegetation map of an entire global biome at a comparable resolution. The consistent treatment of the vegetation across the circumpolar Arctic, abundant ancillary material, and digital database should promote the application to numerous land-use, and climate-change applications and will make updating the map relatively easy.
Full-text available
Dendroclimatological reconstructions may be influenced by intraspecific variation in radial growth caused by plant gender and ecotypic differentiation. We examined the growth response of the High Arctic Salix arctica to interannual variation in snow precipitation in Zackenberg, NE Greenland. Tree ring examinations revealed a consistent response of annual radial growth in this dwarf shrub to variation in the amount of snow precipitation across gender and across three distinct vegetation types. Annual growth, however, differed between vegetation types. These results are discussed with respect to an improved understanding of the factors limiting the growth of S. arctica, which can be used for future reconstructions of climatic conditions, especially in remote High Arctic regions.
Grazing activities and densities of muskoxen in Sverdrup Pass, Central Ellesmere Island, were investigated by use of an automatic camel-a monitoring system from May to August, 1987 and by direct observation from March to May 1988. Average seasonal density of muskoxen was 6.4 +/- 1.9 (S.E.M.) animals x km(-2) resulting in an average of 48.3 +/- 5.1 (S.E.M.) % of available shoots grazed in meadow stands. These figures far surpass previous estimates of density or impact of muskoxen in the High Arctic. It shows that in some high arctic plant communities herbivores can reach high densities and have a high impact, even though aerial survey counts of large areas indicate low average animal densities. Muskoxen selected wet and mesic meadow communities between April and August, except in late June and late July of 1987, when willow herb fields were chosen. In March and early April of 1988 muskoxen grazed valley slopes with little snow cover and little vegetation. In total, 82.8% of the grazing time between 18 May and 18 August 1987, was spent in meadows, despite the fact that these communities covered only 31% of the study area. Muskoxen were therefore highly selective grazers.
Three populations of Cassiope tetragona (Ericaceae) were subjected to in situ environmental perturbations simulating predictions of global warming. The populations were selected to represent different parts of the range of the species, one growing in a high arctic coastal heath at Ny-Alesund (Svalbard, northern part of the species' range), one at a subarctic fellfield at 1150 m a.s.l. at Abisko, Swedish Lapland, and one in a subarctic tree-line heath at 450 m a.s.l. at Abisko, southern part of the species' range. Competition for nutrients and light are the main limiting factors for the growth of C. tetragona near the lower distributional limit of the species, but temperature is the main limiting factor in the northern parts of its range, and at high altitudes in the southern parts of its range. The direct effect of predicted future climatic warming on the growth of C. tetragona will increase towards the north, whereas a possible indirect effect of increasing nutrient availability following a temperature increase will be the main effect in the southern and lower parts of its range. These responses could, however, be modified by shading from other species responding to environmental change by increased growth. -from Authors