Environmental Engineering Reference
In-Depth Information
15.1
INTRODUCTION
table errors may arise from wrongly extrapolating con-
clusions reached elsewhere.
Arctic-alpine ecosystems as used here include the
Arctic and all alpine mountain ranges in the world.
These high - latitude and high - altitude ecosystems
occupy circa 10% of the Earth's surface. They vary
geographically, meteorologically, geologically and his-
torically, in terms of human land use and resource
extraction during the Holocene. Despite their heteroge-
neity, they nevertheless have certain features in
common. For example, the single most important eco-
logical characteristic of Arctic-alpine environments is
the absence of trees, due primarily to their low mean
air temperature during the growth period, which does
not allow tree growth. The vegetation is thus typically
composed of dwarf shrubs, sedges, grasses, mosses and
lichens and is commonly referred to as Arctic and
alpine tundra. The term 'tundra' comes from the Kildin
S á mi word t
ū
nd â r, describing the ' uplands ' , and ' tree-
less mountain tract' found in north-western Russia
where this small ethnic group occurs. Worldwide,
there is in fact a very high diversity of Arctic-alpine
ecosystems. Several overlapping classifi cation systems
categorize comparable ecosystems into zones accord-
ing to temperature conditions and vegetation types.
Table 15.1 compares analogous terms for zones com-
monly found in the literature (Walker
et al
. 2005 ;
Ellenberg & Leuschner 2010) among which are those
used in this chapter. Plate 15.1 illustrates characteris-
tic examples for each zone. Because of the similarities
that exist in the fl oras and the vegetation types of
tundras, not only in the Arctic but also on equatorial
and midlatitude mountains, there has been a tendency
to equate them and to overlook their dissimilarities
(Billings 1973). Since people are now increasingly
using these climatically 'last frontiers', we should be
aware that differences do exist and that many regret-
15.1.1
Specifi c Arctic characteristics
The bioclimatic defi nition of the Arctic does not cor-
respond with the geographic zone delimited by the
Arctic Circle (66.5° N). One reason for this is that cold
waters in ocean currents fl owing southward from the
Arctic bring down the ambient temperatures in Green-
land and the eastern Canadian Arctic, whereas in
Europe, the northward-fl owing Gulf Stream warms the
northernmost landmasses. Thus, at the extremes,
polar bears and tundra are found at and beyond 51° N
in eastern Canada, whereas agriculture is practised in
Norway as far north as 69° N. Consequently, for Arctic
regions there is no general latitudinal temperature gra-
dient comparable to the altitudinal gradient generally
found in alpine regions (see below). In contrast to
alpine environments, mean temperatures during the
warmest month never exceed 10°C, with the exception
of the subarctic zone (see also Figure 15.1).
In the Arctic and subarctic regions, temperature
regime is a key factor for all above-ground and below-
ground biological processes. Due to temperature-
inhibited nutrient cycling within Arctic soils, plant
growth is usually limited by nitrogen and phosphorous
availability (e.g. Shaver & Chapin 1980). Permafrost is
also a common feature. However, the generally low
summer temperature of Arctic environments is partly
compensated by favourable light conditions due to the
'midnight sun', which refers to the period where the
sun permanently stays above the horizon and thus may
provide light for plant growth for 24 hours a day. At
70° N, the midnight sun shines for about 2 months
each year, while at 80°N it lasts for approximately 4
Table 15.1
Comparison of analogous terms for zoning of Arctic and alpine environments according to Walker
et al
. (2005)
and literature within Ellenberg and Leuschner (2010).
Zones
Commonly used synonyms and typical vegetation forms
Arctic
Alpine
High Arctic
Nivale
Polar desert, fragmented patches of cryptogams, perennial grasses and herbs
Middle Arctic
Alpine
Arctic and alpine tundra, dwarf shrubs and grasslands
Low Arctic
Low alpine
Arctic and alpine tundra with possible single trees, grasslands and dwarf shrub
heaths
Subarctic
Subalpine
Taiga, patches of forest, single trees, dwarf shrub heaths
