Epiphytes are plants that grow on other plants but are not parasites nor symbionts because they neither harm their host nor benefit it. Because of the competition for space and light in the forest, many plants have taken up an epiphytic lifestyle and in so doing, have created new microhabitats for other plants and animals to live in. The result is a great addition to forest diversity. Epiphytes are not always obvious because they are often found so high in the canopy, but it is estimated that in fact they make up a staggering 10% of the world’s plant species and within a particular forest ecosystem they may contribute 30% of the total species. They are also some of the most beautiful: bromeliads and orchids are both groups with many epiphytic species.
A tree by itself provides many foods and places to live for a variety of plants and animals. Lichens and mosses can grow on the trunk and stems. Insects feed on the leaves, birds nest and other animals find shelter in hollows. Once an epiphyte takes a hold on a tree, new habitas are created as well. Because they do not have roots in the ground, epiphytes have other ways of catching and holding water and nutrients. These pockets of moisture and soil become homes for other creatures. There are frogs in the rainforest that lay their eggs solely in the pools created by epiphytes and many soil invertebrates find homes in the dirt and leaf litter that collects in epiphytes. The poison dart frog in South America carries its eggs high into the canopy to put them in the water wells of bromeliads. Thus a tree that may by itself provide food and habitat for a few dozen organisms now contains a few dozen more in its epiphytes.
The result to be found in the word’s rainforests is a bewildering variety of new species that exist only in the canopy and in many cases have not yet been described. There are over 30,000 species of epiphytes and who knows how many plants and animals that are dependent upon them for their existence. Each valley in the Amazon, for instance, has its own tree species, its own epiphytes and its own epiphytic communities that could not exist anywhere else.
Many insect species are linked to their epiphytes and are so dependent on them that if the epiphytes die, so do the insects. The dependency works the other direction as well. The flowers of orchids for instance have evolved to resemble the sexual organs of their insect pollinators. The male insects are attracted to these giant ‘females’ and so pollinate the orchids. If the insect pollinator becomes extinct, so will its orchid.
Birds also benefit from epiphytes and worldwide hundreds of species of birds depend on epiphytes for nectar and pollen, fruit, insects and other food items as well as using them as a source of water and nest materials.
Mosses and ferns, lichens and bromeliads, orchids, lianas and creepers, the number of plant families that have taken to the trees is huge, over 80 in total. Obviously the benefits outweigh the drawbacks of this type of existence. Together with their attendant plants and animal, epiphytes contribute enormously to the diversity of forest ecosystems.
References: http://rainforests.mongabay.com/0405.htm http://jrscience.wcp.muohio.edu/fieldcourses07/PapersCostaRicaArticles/Epiphytes.Anecosystemcont.html
