Since they evolved trees have had a great influence on the shaping of the ecology of our planet and in determining the present arrangements of life on earth. Of particular importance for us has been the role of trees in the evolution of mankind and the development of human cultures and communities.
Trees are the largest and longest living organisms on earth. To grow tall the tree has become a miracle of engineering and a complex chemical factory. It is able to take water and salts out of the earth and lift them up to the leaves, sometimes over 400 ft above. By means of photosynthesis the leaves combine the water and salts with carbon dioxide from the air to produce the nutrients which feed the tree. In this process, as well as wood, trees create many chemicals, seeds and fruit of great utility to man. Trees also remove carbon dioxide, the main greenhouse gas, from the air.
Trees are of continued importance to the environment. Tropical rain forests have of particular significance; although they now occupy less than 6 per cent of the land surface of the earth they probable sustain more than half of the biological species on the planet.
Notwithstanding the debt we owe to trees, their emotive power, and their importance to other forms of life, the forested area of the earth is steadily being depleted. This is leading to the degradation of the environment and the extinction of many species. There is now a real danger that in the not very distant future man will destroy a large proportion of the present population of species on earth, create an uninhabitable environment, and then die out himself. If this happens it will not be the first time that a large proportion of the species on the earth have been extinguished.