This months article by Glynne Howels is a thorough introduction to forests, and how they have adapted life around them since the beginning of time.
Today, forests occupy approximately one-third of Earth’s land area, account for over two-thirds of the leaf area of land plants, and contain about 70% of carbon present in living things. They have been held in reverence in folklore and worshipped in ancient religions.
However, forests are becoming major casualties of civilization as human populations have increased over the past several thousand years, bringing deforestation, pollution, and industrial usage problems to this important biome.
Forests in South Africa consist of many small, fragmented and widely distributed patches. They persist in a relatively dry landscape. Fires driven by hot, dry winds during the dry season determined this fragmented location pattern of the forests. Human use and clearing of forests have aggravated this fragmentation.
Largest Forest in KZN
In KwaZulu-Natal the Dukuduku forest is the largest (3 500 ha) but is seriously threatened by uncontrolled settlement of people.
This accentuates the importance of natural forests in South Africa, covering about 0.1 per cent of the country.
Areas of forest in KwaZulu-Natal grow mostly on south facing slopes in higher rainfall areas and along the humid coastal areas.
Different types of forest can be identified by their species composition which depends mostly on the altitude, latitude and substrate (soil and rock types) in which they grow. South facing slopes are favourable for the development of forest as they are more shaded, and therefore cooler and retain more moisture than the northern slopes.
The extra moisture on the south slopes is not only favoured by forest trees, but also helps to prevent or subdue wildfires. The coastal regions are conducive to forest formation because of high rainfall and humidity which are favoured by forest trees and also help to prevent or subdue fires.
Forests are collections of trees and woody plantsand are divided vertically and horizontally. The canopy, midlevel and forest floor describe layers and the ecotone and climax forest delineate its spread on the ground.
Forest conditions require a special set of adaptations for animals to successfully survive and flourish there. The ability to climb or fly will allow escape from predators and easy access to choice food.
Many types of primate live in forests and a number of rodents have evolved the ability to glide from tree to tree using flaps of skin between their limbs. The ability to blend into the shady and leafy habitat makes camouflage an important adaptation.
Striped tigers and spotted leopards and antelope are examples of this. Tree frogs and butterflies, some of them very brightly coloured, are more examples of the ability to blend into the background.
Larger birds of prey such as Crowned Eagles, owls and goshawks who hunt amongst forest trees, have wing shapes that enable them to manoeuvre between trees and also remain silent as they fly.
In tropical forests, being active at night or nocturnal, avoids the high temperatures of the day and the competition from diurnal animals. Good hearing, thick skin, and good eye sight all aid forest dwellers succeed in this environment.
Feet for climbing and gripping forest branches; Tails for balancing or as a third hand; large or long bills for dealing with fruit and hard nuts or seeds.
The leaves of forest trees have adapted to cope with exceptionally high rainfall. Many tropical rainforest leaves have a drip tip. It is thought that these drip tips enable rain drops to run off quickly. Plants need to shed water to avoid growth of fungus and bacteria in the warm, wet tropical rainforest.
Many large trees have massive ridges near the base that can rise 30 feet high before blending into the trunk. Buttress roots provide extra stability, especially since roots of tropical rainforest trees are not typically as deep as those of trees in temperate zones. Forest plants have shallow roots to help capture nutrients from the top level of soil.
Prop and stilt roots help give support and are characteristic of tropical palms growing in shallow, wet soils. Although the tree grows fairly slowly, these above-ground roots can grow 28 inches a month.
Epiphytes are plants that live on the surface of other plants, especially the trunk and branches. They grow on trees to take advantage of the sunlight in the canopy. Most are orchids, bromeliads, ferns, and Philodendron relatives. Tiny plants called epiphylls, mostly mosses, liverworts and lichens, live on the surface of leaves.
On tropical deltas and along ocean edges and river estuaries, trees have adapted to living in wet, marshy conditions. These trees, called mangroves, have wide-spreading stilt roots that support the trees in the tidal mud and trap nutritious organic matter.
Flowers on the forest floor are designed to lure animal pollinators since there is relatively no wind on the forest floor to aid in pollination. In deciduous forests, plants on the forest floor flower in early spring before the trees have grown new leaves so they get adequate sunlight.
Article and Images: G Howells KZN Wildlife