When we think of competition, we usually think of animals competing for food, territories or mates. But plants compete too. It’s true that most plants can make their own food but they need sunlight to do so. Although sunlight is in great abundance and most goes unused, plants in forests, especially rainforests, have to compete for a place in the sun. Walk along the forest floor in a thick, natural rainforest and it will be dark even in midday. Look up and the sky will be obscured by thousands of leaves, filling up the spaces and allowing little sunlight to reach the ground. Seeds can sprout down there but most will die from lack of sunlight to make food.
The solution for some over 30,000 plant species worldwide is to grow on other plants in order to get a foot up as it were in their world and a head start in the race for sunshine. Phyte means plant and epiphyte is a plant that grows on other plants, but they are not parasites. Mistletoes grow on other plants but they sink their roots into their hosts and suck nutrients from their bodies, often killing the unfortunate trees in the process. Mistletoes are true parasites, not epiphytes. Staghorns and elkhorns also grow on trees but they do not take anything from that tree but a place to sit and hopefully flourish, so they are epiphytes, not parasites.
Epiphytes are most common in rainforests because it is in rainforests that the competition is fiercest for sunlight. Many of these plants grow nowhere else but in the canapy and with them are many insects and other animals that are also found nowhere else. The canopy is truly a world of its own.
Of course growing on a tree high in the canopy has problems as well as advantages. Normal plants that grow in soil use their roots to capture water and nutrients from the surrounding substrate. Epiphytes have no such source. They must catch their moisture as it falls from the sky or runs down the trunks and leaves of their substrate tree. For this reason, epiphytes are designed to catch and hold moisture and dust that can provide nutrients.
A great many different types of plants have taken to an epiphytic lifestyle. Mosses and ferns,lichens and bromeliads, orchids and some 80 other families of flowering plants all have epiphytic species among their members. One of the most successful epiphytes are the orchids. These beautiful flowers are especially adapted for life in the canopy, with spreading roots to capture moisture and nutrients, pockets to hold water during dry seasons and flowers cunningly designed to attract insect pollinators, often specific insects that feed nowhere else and have evolved with their hosts. Orchids also produce millions of tiny wind-born seeds. Many undoubtedly fall on unsuitable habitats but a few find new trees in which to grow and flourish.<?xml:namespace prefix = o ns = “urn:schemas-microsoft-com:office:office” />
One of the strangest plants to take to the canopy are cacti. Epiphytic cacti are quite different from their desert cousins. Desert cacti have spines for protection from herbivores and waxy leaves for moisture retention because they get their moisture from the ground. Epiphytic cacti lack spines and their leaves are broader and without a waxy covering so they can absorb moisture from rain or clouds. They have adapted beautifully to their changed lifestyles and are living examples of evolution in action.
The fates of epiphytes are tied to their trees. When a rainforest giant is felled, a whole ecosystem dies with it: its epiphytes and all the insects and other animals that were dependent on them. The tragedy of wholesale rainforest clearing is the loss of thousands, perhaps millions of species, many unknown to science, that flourished with their trees until the coming of humans and their chainsaws. Saving the rainforests is not just about big trees and signature species such as the jaguar. It is also about epiphytic orchids and cacti and a multitude of other plants and the animals that depend on them. Are our current resource needs really so great that we can justify the destruction of so much when we don’t even know what we are destroying? Or is our greed something for which we will be cursed by future generations who we are robbing of their priceless heritage? Its something to think about next time one considers what timbers to buy for the architraves of a new house. Some trees are much more valuable alive than dead.
References: http://rainforests.mongabay.com/0405.htm
