A view from the air--Where have the forests gone? (Sierpe River Area, SW Costa Rica)
Epiphytes play an important role in tropical rainforest diversity and productivity and take a massive part in creating unique habitats for animals that cannot be found in any other place of the world. The word epiphyte is formed from epi-, meaning upon, and phyton, meaning plant. Epiphytes grow on plants having their root structure off the ground instead of in the ground. Because their root system is in the air, they have evolved to be able to live in a harsh environment. Not only have epiphytes found a way to live high in the rainforest canopy, but also they are able to host micro-ecosystems and a variety of wildlife. This paper will review how epiphytes live in the rainforest canopy, and how they support life and diversity in the rainforest.
Epiphytes in the Neotropics
Epiphytes are a major component of rainforests because of their wide variety and large abundance. Mostly living in the tree canopy, they can account for 33 percent of the plant species. Epiphytes were found to even hold 50 percent of the nutrients in some rainforests (Yanoviak 2003). They are the most prevalent in cloud rain forests due to the high availability of water in the form of rain and mist. Epiphytes were able to account for 40 percent of the biomass of all the plants, trees, and shrubs in some Neotropical cloud rainforests (Nadkarni 1989). There are over 83 different kinds of epiphytes including orchids, cacti, bromeliads, aroids, lichens, mosses, and ferns. Half of the world’s 30,000 species of epiphytes live in the neotropics (Butler 04/10/2007).
Epiphytes are not parasites to the plants that they live on, but rather obtain their nutrients and water from the air and rain while obtaining energy from the sun. If it were a parasitic relationship, one plant would benefit at the host species expense. Epiphytes do not harm their host species by only using the host for support and epiphytes often benefit the host tree or plant. In some cases, host trees were able to grow aerial roots when their branches were populated by epiphytes, enabling them to take in water and nutrients that were collected in the dense layers formed over time by the epiphytes (Kricher 31).
Living in the Canopy
In order to survive, plants must be able to obtain water and nutrients. Since they do not have roots in the ground, they have to be efficient in collecting rain and nutrients. Epiphytes form dense root systems that have a large surface area, enabling the plants to absorb rainfall. Since water might be limited and there might be long lengths of time in which it is dry, many epiphytes such as orchids are able to store water in thick stems. Other epiphytes are able to collect water in their leaves, enabling them to have a supply of water during dry periods of time. It is also important for epiphytes to collect nutrients. In Manaus Brazil, rain brought 3 kilograms of phosphorous, 2 kilograms of iron, and 10 kilograms of nitrogen annually to one hector of forest (Butler 4/10/2007). Nutrients are also available from dust and particles that are caught in the roots and nutrients from decaying organisms.
There are several benefits of living in the canopy that give epiphytes an advantage. First, epiphytes are able to get much more sunlight in the canopy than they would be able to get when living on the ground. Since they live on trees, the epiphyte does not have to use energy to reach high into the canopy from the forest floor and compete with trees and vines. Reproduction is a benefit of living high in the tree canopies. Wind, insects, and birds are all important factors in reproduction of most plants. The canopy is the liveliest place in the rainforest with hundreds of birds and thousands of insects. The more organisms that come in contact with the epiphyte, the more likely that it will be pollinated and its seeds distributed. The wind is also very important to most epiphytes. Orchid epiphytes have adapted to have hundreds of thousands of seeds that measure in microns that are able to float in the air over long distances and find a landing spot in another tree. Wings on seeds insure that the seed will not fall straight down to the floor, but rather be able to travel to a new place in which it can grow thus increasing its distribution and range (Butler 4/10/2007).
Epiphytes make up a huge part of the biodiversity in a rainforest. Not only do epiphytes account for a large portion of foliage in rainforest, they also support other plants and organisms. Every epiphyte is a microhabitat, in which there can be a food web of arthropods and other animals.
Non-vascular epiphytes such as bryophytes, liverworts, and mosses, can be a home for many arthropods. Young forests will accumulate dense coverings of these epiphytes on the bark and on the branches. In old growth forests, epiphytic mats are formed from years of growth and the accumulation of particles and dead tissue. These mats tend to contain insects including mites, springtails, beetles, ants, moth larvae, thrips, bark lice, wasps, and spiders. The insects thrive while living in the epiphytes in the rain forest canopy, but when they die they help to supply the epiphytes with nutrients and minerals (Yanoviak 2003).
An example of a vascular epiphyte that can host a microhabitat is a tank bromeliad. Tank bromeliads have stiff upturned leaves that create a cup that collects and holds water. Some tank bromeliads have been found to hold up to two gallons of water when completely full in which the plant can use as a water supply and a source of nutrients. Being able to collect water is important to the plant, but the small pool of water is also important to many unique species that depend on the bromeliad. Frogs, mosquitoes, flat worms, insects, snails, salamanders, and crabs can all be found inside the water of a tank bromeliad. Some poison dart frogs use the plant to raise their young due to pooled water and supply of insects and larvae. The female frog lays her eggs on the forest floor, and when the eggs hatch she carries the tadpoles up to the epiphyte. They will then feed upon the larvae of different insects that are suspended in the water (Butler 4/10/2007).
Epiphytes are also a home to ants, including the stinging ant. Certain Bromeliad epiphytes contain chambers that are connected by holes and tunnels. The chambers give a place for the stinging ants to live, store food, and reproduce. Not only do the ants benefit from the situation, but the bromeliad benefits too. The ants protect the plant from insects and animals that would eat the leaves and also supply the plant with nutrients. Wastes from the ant colony decay and the bromeliad is able to absorb the nutrients so that it can live and grow in the canopy.
Another group of animals that are greatly benefited by epiphytes are birds because of the many resources that epiphytes have to offer. Resources that epiphytes provide are flowers, nectar, fruits, insects, water, and material to use to build nests. It was found that over 193 species of birds use epiphytes to obtain food and nutrients. Frugivores, insectivores, and nectarivores all rely on epiphytes for food along with many species of birds that use epiphytes for nesting. The most common birds that use epiphytes are tanagers (Thraupidae) and hummingbirds (Trochilidae). A study showed that 60 percent of birds in an area used epiphytes in foraging, showing that epiphytes are responsible for supplying a large amount of food to bird species (Nadkarni 1989).
Researching the Canopy
Even with systems to explore the rain forest canopy that have been developed through the years, it is extremely hard to explore the canopy. By using platforms, cranes, walkways, and ropes, scientists have tried to explore the huge amount of diversity contained in the forest crown and in the epiphyte layers.
The most efficient way off finding what arthropods that are supported in the tree canopy and in the epiphytes is by fogging. Insecticide is sprayed into the canopy, killing arthropods and causing them to fall off of leaves and branches to the ground where they are collected. With this method, researchers are able to test many sites that would be challenging to test other ways, but can pose many problems too. Only part of the insect population makes it down to the bottom of the trees. Studies show that many small insects caught in the epiphytes and populations are never documented (Yanoviak 2003).
To get more accurate measures of the epiphytes and the organisms that rely on them, researchers must be able to reach the canopy themselves. One of the most useful ways of collecting information in the forest canopy is by using construction cranes. Since being first used in 1990, researchers have learned a lot about diversity and productivity (Lowman 2001).
Still, there is a lot to be learned about biodiversity within and between rainforests. Until recently, information gathered by scientists was not shared with people researching other forests on opposite sides of the globe, but thanks to computers, information is shared on a global level. Computer bulletin boards allow scientists to share their information on different field sites, enabling research to take place on a global level (Lowman 2001).
Without question, epiphytes are one of the most important plants in the rainforest. They are a major producer of food for many of the organisms of the rain forest, and they are the home of many arthropods. Unfortunately, 100 epiphyte orchids alone go extinct every year due to deforestation and farming (Butler 4/10/2007). Without epiphytes, Neotropical forests would not be able to support the diverse amount of plants and animal life. It is worth the resources to research this important group of plants learn out more about how they can support such a diverse ecosystem.
Benavides, Ana M., Alvaro J. Duque, Joost F. Duivenvoorden, Alejandra Vasco, and Ricardo Callejas. "A First Quantitative Census of Vascular Epiphytes in Rain Forests of Colombian Amazonia." Biodiversity and Conservation (2005): 739-758.
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Butler, Rhett A. "Tropical Rainforests: the Canopy." Mongabay. 2007. 10 May 2007
Holscher, Dirk, Lars Kohler, Albert I.j.k. Van Dijk, and Sampurno Bruijnzeel. "The Importance of Epiphytes to Total Rainfall Interception by a Tropical Montane Rain Forest in Costa Rica." Journal of Hydrology 292 (2004): 308-322. www.sciencedirect.com.
Kricher, John. A Neotropical Companion. 2nd ed. Princeton: Princeton UP, 1997.
Lowman, Margaret D. "Plants in the Forest Canopy: Some Reflections Onn Current Research Aand Future Direction." Plant Ecology 153 (2001): 39-50.
Nadkarni, NaliniM and Teri J. Matelson. "Bird Use of Epiphyte Resources in Neotropical Trees." The Condor (1989): 891-907.
Winkler, Manuela, Karl Hulber, and Peter Heitz. "Population Dyanics of Epiphytic Bromeliads: Life Strategies and the Role of Host Branches." Basic and Applied Ecology 8 (2007): 183-196.
Yanoviak, Stephen P., Nalini M Nadkarni, and Jon C. Gering. "Arthopods in Epiphytes: a Diversity Compnent That is Not Effectively Sampled by Canopy Fogging." Biodiversity and Conservation 12 (2003): 731-741.
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