Rainforests are such diverse ecosystems that it is surprising to learn that most are growing on thin, poor soils that contain few nutrients. The key to the luxurient growth of the rainforest is dependent not on new nutrients but instead on the recycling efforts of least obvious members of the ecosystem: the saprophytes and other decomposers.
Saprophytes are fungi. These organisms, along with bacteria, are responsible for breaking down dead organic material and thus making it available to the ecosystem. Without them, the organic material would be on a one way trip to nowhere and once it was used up, there would be no more. But when a tree falls in the rainforest, the saprophytes take over. Fungal hyphe grow through the wood, reducing it to its basic compenents, even the difficult to digest lignins. Once in the soil, new trees can take up the nutrients and turn them back into living tissues and the cycle of life can continue.
Fungi are important in all ecosystems. Without them, as my ecology teacher once laughingly put it, we would be neck deep in dead elephants. All ecosystems are limited by the available nutrients but some are richer than others. The plants growing near volcanoes are able to break down the igneous rocks and use the elements in them to create new organic matter. Rainforest plants often do not have that advantage. Many rainforests are so old that all the available nutrients have been extracted from the soils and tied up in the riot of vegetation that makes up the ecosystem. So the quicker dead organic matter is recycled, the better for all concerned.
Fungi are masters of their realm. They can grow quickly, putting out new hyphae to find new sources of food. In the wet tropical rainforests they can move quickly into newly dead material and with the help of worms and bacteria and saprophytic insects such as ants and termites, make the material available for the next generations of plants and animals. Thus they may not be the most obvious members of their ecosystems but they are just as important for the survival of the rainforest as the most impressive giant trees.
Humans discover this at their own cost. Rainforests are often razed for their timber and then sown with grasses in order to grow cattle. However the destruction of the trees also leads to the destruction of the saprophytes and thus the soils. What is left is very poor indeed and within a few generations, the land becomes a desert instead of one of the most productive anddiverse ecosystems on earth. This is another important reason why we should be conserving the rainforests of the world instead of destroying them for short term profits for the greedy few.
