ABSTRACT
The contribution of the component parts of the tree to the total biomass varies with the age of the individuals and the developmental stage of the forest ecosystem—the ratio of woody non- photosynthetic to green photosynthetic material increasing with age. In some circumstances, as in the tropical rain forest, the development of a multi-layered tree canopy may reduce light to an extent which limits the growth of smaller non-arboreal forms beneath it. The characteristically high productivity of forest ecosystems is also related to their structural development which allows the use of a large resource volume. As a consequence of its massive biomass, the impact of the forest on the atmosphere and soil it occupies is greater than that of any other ecosystem. Modification of temperature and air movement is accompanied by that of atmospheric humidity; this can be as much as 11 per cent higher in temperate forests, 15 per cent in tropical forests than in the free atmosphere.
