|
A forest is a community of living organisms which rely on one another for their existence. The forest ecosystem is the interaction of the living organisms and their physical environment. In a plantation forest community those interactions produce energy in the form of food being passed on from one trophic level (feed level of an organism) to another along food chains. Linking of food chains results in food webs.
| Typical Food Chains |
| Producer |
1st level consumer |
2nd level consumer |
3rd level consumer |
|
|
Forest tree
root sap |
Cicada nymph |
Centipedes |
Blackbird |
|
|
Forest tree
root tip |
Cicada nymph |
Spider |
Kiwi |
|
|
Forest tree
foliage/bark |
Insect |
Fantail |
Stoat |
|
|
Energy Flow
As energy in the form of food is passed along the food chain, some is lost at each trophic level. As a first level consumer (herbivore) eats the plant material, some of the energy material is used by the animal for growth, repair of body tissues and movement. The herbivore loses energy from the food in the form of heat from respiration and in its waste products.
This energy loss occurs at each trophic level and there must always be more energy in the lower trophic level to sustain the life in the level above.
Click on the forest ecosystem diagram.
Plantation Food Chains
The three main living components of a forest are:
• Producers
• Consumers
• Decomposers
Producers are plants which make their own food by photosynthesis. The main producer in the New Zealand plantation forest will be radiata pine although there are many other plant species on the forest floor.
Consumers are the animals which do not produce their own food. Animals that eat plants are herbivores, animals which eat other animals are carnivores and omnivores eat both plant and animal tissues.
Decomposers break down dead plant and animal material and wastes and release it again as energy and nutrients into the ecosystem for recycling. Organisms that live on dead material are called saprophytes.
Pine Decomposition
Decomposers play a very important role in recycling nutrients in a forest. The pine needle litter on the forest floor is the habitat of many small animals. Millipedes, insect larvae and slaters break down the needles into small pieces by chewing. The wax and resin in the needles slow down the decay process.
Woody parts of the tree are attacked by beetles and termites. Their guts have bacteria that can break down the cellulose in the wood. Holes made by these beetles are made bigger by fungi which invade the holes. Fungi and bacteria finally decompose the pine residues and convert them into materials for recycling.
Pine needle litter is slow to decompose when the forest is still standing because the mycorrhizae fungus associated with the roots of the trees inhibits decay. When the trees have been felled the amount of this fungus is reduced and decomposition is more rapid.
Beneath the soil, subterranean animals such as earthworms and cicada nymphs break down the humus and convert it to soil. Earthworms are not as numerous in a forest as on farmlands.
Species Interactions
In a forest, ‘consumers’ specialise in the type of food that they eat. This reduces direct competition and allows a greater diversity of species.
Through niche specialisation, organisms fill particular roles in the community. In a pine forest many insects have developed special feeding habits and feed on different parts of the tree to avoid competition:
• Foliage. Defoliaters include the white fringe weevil
which eats the adult foliage and Heliothis armigeria
which eats the soft ends of young needles and buds.
• Wood and bark. The red-haired dark beetle attacks
dead branches of living trees. The larvae of the pine
bark anobiid feeds on the bark and sapwood. The wood
wasp lays eggs in living trees and deposits mucus and
fungus into the wood, causing the foliage to wilt. Larvae
then chew their way into the tree.
• Roots. Cicadas, grass grubs and larvae of the white
fringe weevil eat the roots.
• Sap Sucking. Thrips.
• Cone and Seed. Cicadas and aphids.
Birds also have niche feeding positions although the pattern is not as distinct in New Zealand as it is in European countries which have greater bird numbers. Here, birds tend to overlap feeding niches because competition for food is less intense.
Birds that can be seen feeding in different positions in a pine plantation:
• Fantail. Hovers near the tops of trees eating small
insects.
• Grey warbler. Hovers at the tips of fine branches and
picks off caterpillars.
• Whitehead (North Island) and brown creepers (South
Island). Feeds on insects among the branches.
• Rifleman. Feeds on insects found in crevices on the
trunk and heavy branches.
• Pied tit (North Island) and yellow breasted tit (South
Island). Perch on branches and feed on caterpillars and
beetles. Also eat invertebrates on the forest floor.
• Robin. Hunts grubs in the forest litter.
Organisms have evolved over many years to have the shape, mouthparts, legs and other body adaptations to allow them to survive in their niche area.
|