Geography Reference
In-Depth Information
through the taiga forest. Smaller mammals, such as weasels, tend to
be camouflaged with fur that changes colour in winter.
Wildfire is an important feature of the taiga. Fire is helpful in
nutrient cycling, speeding up an otherwise very slow process,
removing a thick, acid, litter layer (which may have been keeping
more of the ground frozen for longer). Lightning strikes can initi-
ate large fires perhaps at 200 year intervals. These disturbances clear
land to ensure there is a good species mix but species are also
adapted to fire with many conifers, shrubs and herbs sprouting
from roots, stumps and underground stems or having long seed dis-
persal periods (e.g. from pine cones).
There is a gradual transition between the southern taiga and
tundra to the north with trees becoming sparser in colder con-
ditions. Tundra is the rather flat, treeless zone between the taiga
and the polar ice. These regions are harsh for life: summers where
temperatures rise above freezing may only last a month or two;
winters may see temperatures as low as -50°C. Strong, cold, dry
winds are common, with little precipitation. Permafrost with a
shallow active layer inhibits plants with deep roots and soil animals.
The soils are shallow with acid litter above a gleyed horizon and
then a permanently frozen layer. There is very low productivity
and species richness with low growing, woody, herbaceous plants
and mosses and lichens. Growth rates can be so slow and summers
so short that some plants produce flower buds one summer ready
for opening and pollination the next year. The low productivity
means that these areas can be susceptible to human damage as
recovery rates would be very slow indeed (e.g. from tyre tracks,
mining etc.), leaving marks for hundreds of years. The low pro-
ductivity also means that large areas of land are required to support
any herbivores (e.g. rodents or migrating herds of reindeer and
caribou) or carnivores (e.g. owls or foxes). Lemmings are import-
ant in the tundra zone as they increase the rate of nutrient cycling
among the soil and plants and can even stimulate growth rates
through their grazing action. They act as important prey for carni-
vores but the population of lemmings changes over cycles of a few
years having knock-on effects for the rest of the ecosystem.
