The tranquillity of the forest environment which appeals to so many visitors masks a massive amount of continual biological activity.
New Zealand’s natural forests contain around 20,000 tonnes of carbon per square kilometre. The plantation forests absorb even greater amounts because they grow faster – estimated at a further 20 million tonnes of carbon annually.
In stable natural ecosystems the uptake and release of energy and carbon are more or less in balance with the plant and animal species contributing about equally to the cycle of growth and decomposition.
The position of each plant and animal species within the forest system is determined by the characteristics of the organism itself. Some need strong light and will be found in the upper canopy, others need moisture and will thrive in the relatively high humidity on the ground.
The forest is a kaleidoscope of habitats almost beyond imagination and the various adaptations both plants and animals have made to take full advantage of these is equally amazing.
Upper Canopy
The upper canopy includes plants able to tolerate direct exposure to the sun and wind. These are usually the large trees, but also include epiphytes (plants which perch on the stems and branches of others to get access to light) providing shelter and shade for species lower in the canopy and on the ground.
The leaves of the upper canopy tree are often tough and leathery to withstand damage or drying when moisture is less readily available. The animal life of the upper canopy is also adapted to its position. Birds are fliers and usually brightly coloured and readily visible to one another.
Lower Canopy
Plants nearer the ground are less woody and tend to have larger and softer leaves, better able to catch the available light and with no need to defend against the buffeting of the wind and rain. Birds in the lower tiers of the forest tend to be poorer fliers and less colourful such as the kokako which is bluish-grey and has distinct blue wattles. New Zealand’s two native mammals, the short and long-tailed bats are now rare, but would usually inhabit this zone, relying on their keen sense of sound and sonar system to guide them through the forest to their insect prey.
Forest Floor
The forest floor is an area of perpetual shade and often quite high humidity. Plants must be able to exist with the minimum of light and they are often quite soft and fragile. A number of filmy ferns and orchids are among the species commonly found on the floor of New Zealand’s natural forests. Bird life may include non-flying species such as the kiwi, which also has little sight and relies on keen senses of smell and hearing. The moist conditions are also suitable for the three species of native frog, all of which are able to exist without access to open water. There is also a range of native lizards (skinks and geckos) which thrive in the moist vegetation.
Beyond the Trees
The forest habitat extends beyond the trees themselves to include the many streams, swamps and lakes it is associated with. The thick carpet of decomposing litter under the forest is a huge sponge, gradually releasing stored rainwater. This slowly filters through the litter and is clear, clean and almost constant in temperature. Plants, fish and insects that live in these water systems are also protected by the forest’s influence on their habitat.
Planted Forests
Plantation forests are not habitats of the same quality as natural forests, particularly when first planted, due to intensive site preparation and reduced species diversity. However, as the trees mature, many of the characteristics of natural forests develop, reflecting the fact that conditions in planted forests remain settled for long periods. Many native plants and animals have found a satisfactory home in our plantations, including kiwi and the kokako. Shrubs and ferns also tend to establish well and there is usually a significant improvement in water quality once the new forest is growing.