14 Temperate forest

Temperate forests are located almost entirely in the Northern Hemisphere, although they do occur in the Southern Hemisphere at the tips of Africa, South America and Australasia.

The rainfall in this biome averages 80-150 cm a year and is fairly evenly spread over the year. The summers are typically warm and the winters are cold, often falling below zero degrees Celsius.

Temperate forests usually consist of two layers - the canopy and an understorey of shrubs. Unlike in the rainforests where little light penetrates to the forest floor, in temperate forests there is enough light for herbaceous plants and moss to grow. There are also less tree species in temperate forests than in the rainforest. The perennial plants that grow on the forest floor tend to die away in the winter and come up again in the spring.

There are several different types of temperate forest. These are:

• Broad-leaved deciduous woodland (western Europe, eastern North America), including oak, beech, chestnut and ash.

• Coniferous forest (Pacific coast of North America), made up of redwood, red cedar and hemlock.

• Mixed conifer and deciduous (Great Lakes region), containing birch, oak, hemlock, pine and maple.

• Broad-leaved evergreen forests (Japan and Tasmania), include southern beech and chinquapin.

At higher latitudes the forests are typically coniferous, and in warmer regions they tend to be deciduous.

The leaves of deciduous trees change colour in the autumn, as chlorophyll, the green pigment, breaks down. The leaves turn golden, red or brown before falling off the branches. This is because water is in short supply, and so to conserve this precious resource, the trees sacrifice their leaves in the winter.

This is one of the most heavily populated biomes. If it were not for the long history of forest clearance for agriculture, industry and cities, a great deal more of the temperate world would be covered by woodland. Much of the ancient forest has been replaced by heathland and moorland. Ten thousand years ago the UK was almost entirely covered by forest, with coniferous pines in the north and oak, lime, elm, hazel, birch, alder and ash in the south.

(2170 signs)

15 Layers of the Rainforest

There are four very distinct layers of trees in a tropical rain forest. These layers have been identified as the emergent, upper canopy, understory, and forest floor.

• Emergent trees are spaced wide apart, and are 100 to 240 feet tall with umbrella-shaped canopies that grow above the forest. Because emergent trees are exposed to drying winds, they tend to have small, pointed leaves. Some species lose their leaves during the brief dry season in monsoon rainforests. These giant trees have straight, smooth trunks with few branches. Their root system is very shallow, and to support their size they grow buttresses that can spread out to a distance of 30 feet.

• The upper canopy of 60 to 130 foot trees allows light to be easily available at the top of this layer, but greatly reduced any light below it. Most of the rainforest’s animals live in the upper canopy. There is so much food available at this level that some animals never go down to the forest floor. The leaves have “drip spouts” that allows rain to run off. This keeps them dry and prevents mold and mildew from forming in the humid environment.

• The understory, or lower canopy, consists of 60 foot trees. This layer is made up of the trunks of canopy trees, shrubs, plants and small trees. There is little air movement. As a result the humidity is constantly high. This level is in constant shade.

• The forest floor is usually completely shaded, except where a canopy tree has fallen and created an opening. Most areas of the forest floor receive so little light that few bushes or herbs can grow there. As a result, a person can easily walk through most parts of a tropical rain forest. Less than 1% of the light that strikes the top of the forest penetrates to the forest floor. The top soil is very thin and of poor quality. A lot of litter falls to the ground where it is quickly broken down by decomposers like termites, earthworms and fungi. The heat and humidity further help to break down the litter. This organic matter is then just as quickly absorbed by the trees’ shallow roots.

(2082 signs)