The wonder of trees

Trees - our observation wanders to identify their residence. Spectacular, ghostly, gigantic, evergreen, all are engulfed in their particular habitat. The Daintree in Northern Queensland is 110 million years old, when dinosaurs ruled the land!

In a virgin forest, growth keeps pace with decay: a tree will be reaching maturity, another declining. As an old tree falls, a gap is made in the canopy, light is let in and many young trees race with each other to occupy the new opening and the rhythm is maintained.

When a tree stops growing it begins to decline. Decay may have set in within its heart and it is attacked by beetles and borers and its roots by fungi. Its huge body is no longer supported and a mere gust of wind brings it to earth. It becomes a home for woodlice and millions of insects, which play their part in returning the fallen tree to the earth from which it sprang.

It has taken centuries to form the floor of the forest. Up to 90 per cent of mineral soils are derived from rocks by a process of "weathering", carried on by alternate freezing and thawing, contraction and expansion, as a result of cold and heat, the action of water and carbonic acid, and prying action of roots.

Maybe a forest of today is standing on a site which at one time was bare rock. Some lichens established themselves on a damp level surface. The weathering action of the elements disintegrated the surface and formed a layer of tiny rock particles. This process was hastened by the chemical secretions of the lichens until these mosses were followed by grasses; and then one day a wind-borne tree seed lodged there and began to grow and thus founded a community of trees. This process developed as from the Ice Age.

The forest floor is the name given to the ground beneath the trees in a forest. The mulch is made up from fallen twigs and leaves which remain on the ground where they slowly decay and form a cover of rich mould or humus. This protective covering forms a most useful purpose. It permits the rain and snow waters to permeate the soil without making it too compact, thus allowing the air to penetrate, while at the same time it prevents the washing away of the land and the too rapid or excessive evaporation from the surface.

The humus also assists the decomposition of the mineral substances in the soil, which in turn provides food for the growing trees. It takes time for the rainstorm to penetrate the leaves and still longer for it to percolate through the humus and longer yet to find its way through the root channel to the subsoil where later it will form springs, which in turn will feed rivers. It is one of the most valuable functions of the forest to provide catchments areas and so distribute water for growing crops.

It has been shown that trees are not exacting on the quality of soils because they make their own manure and fertilise themselves, and even provide a surplus. Practically all trees make their best growth in full sunlight but various are adapted to survive impartial shade. It is the crowding of trees in the forest which helps them in their upward growth and kills off the lower branches.

Trees are forever working for man's good. During the day the ground under the trees is protected from the sun's rays and is cooler than soil unprotected. At night trees retard the radiation of heat from the ground under them. This helps to equalise the temperature.

Forests have the potential to contribute to climate change through their influence on the global carbon cycle. They store large quantities of carbon in vegetation and soil, exchange carbon with the atmosphere through photosynthesis and respiration, release carbon into the atmosphere when they are disturbed, become atmospheric carbon sinks during regeneration after disturbance and can be managed to alter their role in the carbon cycle.

We cannot yet clearly follow the intricacies of the circulation of water in the earth, in the trees, in the ocean and in the air; but we do know that man's ignorant interference with the forest and other cover has greatly reduced the earth's fertility and is still doing so...

Light and temperature play important parts in producing the autumn colours of trees. Low temperatures and gradually shorter days are the signals that lead to the breakdown of chlorophyll (the "green" colour) in leaves. As the chlorophyll breaks down, we begin to see the red and yellow pigments that were masked by the chlorophyll while the leaves were expanding and growing during spring and summer.