Geography Reference
In-Depth Information
extremely sparse and organic matter inputs are therefore low.
Where water is concentrated, the habitat improves but most of the
biomass is underground. Adaptations focus on maximising the con-
servation of available water; cacti store lots of water within their
stems; leaves are often replaced by thorns. The creosote bush has a
wide distribution of roots which put toxins into the soil to prevent
other seeds, including those of the creosote, from germinating to
ensure there is no competition for water. The woodiness of many
desert plants helps stop the collapse of plant material during wilting.
Grasses tend to be short and tufted to protect against drought and
heat. Lengthy dormant seasons are common for plants. Seeds often
only germinate when the conditions are wet, perhaps many years
after they have been deposited. This can mean there is a sudden
bloom of life during a wet period and then offspring are not seen
until the next wet event. Animals are adapted to reduce moisture
loss either by being nocturnal or only producing small amounts of
urine. Some animals and plants are designed to capture dew, such
as the Namib beetle.
Mountain biomes
Topography can be an important factor influencing biomes. High
mountains usually exhibit strong contrasts in the ecosystem with
altitude. The zones that can be identified vary widely between
mountain regions but a typical classification may involve: a hill
zone where the flora and fauna is related to that in the lowlands; a
montane zone which contains species that are common to moun-
tains but usually dominated by deciduous forest; a sub-alpine zone
dominated by conifers with shrubs at the upper fringes; an alpine
zone lacking in trees with vegetation that is short with grasses,
sedges and plants with flat, spreading growth with reduced leaves
and often with colourful flowers; and a snow zone which has sparse
vegetation consisting mainly of mosses and lichens leading up to
the permanently covered ice and snow zone.
HUMAN IMPACT
Humans have modified the biosphere by overexploitation of species,
deforestation and extinctions, the distribution of species either
