Geoscience Reference
In-Depth Information
low nutrient-supplying power of soils, as witnessed by the
lush growth when nutrients are added in reseeding and
fertilization experiments carried out near development
sites, and also from the response of plant growth to nitrate
and phosphate provided by animal and bird droppings.
Rich patches of vegetation are found beneath bird cliffs,
around animal burrows, in muskox meadows and even
around rotting skeletons.
There are numerous adaptations to these hostile
factors. Low growth (
Plate 24.16
)
and rosette and cushion
shapes are obvious ones (
Plate 24.17
).
More specialized
adaptations include high biomass ratios of roots : shoots,
and
vivipary
(production of bulblets instead of seeds),
autogamy
(self-pollination, removing dependence on
insects) and a high incidence of
polyploidy
or genetic pre-
adaptations, thought to facilitate colonization of new
substrates. These are essential to plants where late-
surviving snow beds severely attenuate the growing season
to less than fifty days. Biogeographers are even able to map
the extent of late snow beds by the distribution of
chionophilous (i.e. snow-loving) vegetation like arctic
bell heather (
Cassiope tetragona
). Further ecophysiological
survival adaptations include heliotropism, cryopreserva-
tives in cell sap, nutrient storage mechanisms and a
delayed growth cycle over more than one short summer.
The ability to grow slowly and to suspend growth in
unsuitable times is shown by the high biodiversity of
mosses and lichens in arctic-alpine regions, although they
are also favoured by the lack of overshading by higher
plants. Due to the risk of physiological drought, especially
when air temperatures rise in spring, whilst soils remain
frozen, many arctic and alpine plants have xerophytic
adaptations such as hairy stems and small leaves more
usually found in dry areas.
treeline shows the result of wind blast on the upwind side of
the tree.
Photo: Bill Archibold
(or
geophytes
) with subsurface bulbs and corms,
hemicryptophytes
with buds at the soil surface, and
chamaephytes
with buds just above ground level. Tundra
typically has
Biodiversity in comparison with
temperate regions
Vegetation in polar latitudes is generally less diverse than
in temperate climates, though there may be a greater
abundance and diversity of plant species in alpine regions.
The current state of knowledge about the Arctic's
biodiversity is 1,735 species of flowering plants, 600
mosses, 2,000 lichens, 2,500 fungi, seventy-five marine and
terrestrial mammals, 240 birds, 3,300 insects, 300 spiders
and five earthworms.
Ecological communities near the poles reflect the
extremes of the environmental and biological gradients at
which they are located. Whereas temperate regions
have relatively warmer and more stable environments,
which support species-rich communities, adverse and
50 per cent hemicryptophytes. They must
complete their annual cycles within a relatively short
growing season, and in winter plants need to survive wind
blast, snow blast, snow burial, physiological drought
brought by exposure to air streams and frequent ground
disturbance by frost. Plants also have to contend with a
variable extent of bare rock or debris surfaces.
Adverse growing conditions in the arctic are the
negative radiation balance and consequent low tempera-
tures, low soil nutrient contents, and strong winds. Low
soil nutrient contents result from the slow rates of organic
matter mineralization, soil weathering and soil chemical
reactions generally. Plant growth is severely limited by the
