Geography Reference
In-Depth Information
characteristic animal communities. The location of the major global
biomes is shown in Figure 5.1. Climate is the main driver of the
location of biomes, with temperature and precipitation regimes
being crucial. The ocean is not really divided into biomes but there
are roughly horizontal layers which support typical plants and
animals.
Cold biomes
The cold biomes consist of the area including the forested taiga to
the treeless tundra. Note from Figure 5.1 that these biomes are
restricted in the southern hemisphere due to a lack of ice-free land
at high latitudes. The cold biomes are therefore often called the
Boreal zone (which means the northern zone).
The taiga extends north from where the monthly average tem-
perature of 10°C occurs for less than five months of the year up to
where only one month has an average temperature above 10°C.
The growing season is therefore short and soils are often thin
because large areas have been eroded by former ice sheets and soil
development is slow due to cold temperatures. The lack of soil
animals means that decomposition is limited and there is an acidic
leaf litter. In many areas, large expanses of peat have developed due
to impeded drainage caused by the underlying fine glacial deposits.
The taiga forests of Europe and Asia consist mainly of conifer-
ous trees such as Norway Spruce and Scots Pine in the west but
there is more deciduous larch in the east. In North America,
Lodgepole Pine and Alpine Fir dominate in the west and White
Spruce, Black Spruce and Balsam Fir in the east. Tree growth rates
are slow, especially in the colder areas with a height gain of perhaps
15 centimetres per decade, but evergreen species are able to photo-
synthesise as soon as conditions are right rather than having to wait
for leaves to develop. The forest structure is simple with an ever-
green canopy and then ground level tufted grasses, mosses, lichens
and heathland plants such as bilberry. Tree cover is not dense
everywhere and there are more open areas especially where it is
colder or where soils are very thin. Active layer processes in per-
mafrost can cause ground instability that can fell individual trees.
Where tree cover declines the ground is often covered with
lichens. Caribou (North America) and reindeer (Europe) migrate
