Tuesday, March 16, 2010

The Forest Canopy

A forest canopy consists of the area above the forest floor where tree crowns containing branches and leaves meet. At 200 feet (61 m) or more above the ground, the canopy performs more than 90 percent of a forest’s total photosynthesis because it is the portion most exposed to sunlight. For that reason the canopy stores 60 percent or more of the Earth’s carbon while supporting a food web that is more diverse than any other. Carbohydrates made in photosynthesis provide the foundation for food webs that live solely in the canopy and also for ecosystems that extend to the forest floor.

Tropical, temperate, and boreal forests each have their own unique canopies, but there are basic similarities among them. The canopy’s overstory contains towering trees spaced closely together so their branches and leaves form a continuous community. The understory consists of more widely spaced shorter and juvenile trees. Because forests across the globe receive different amounts of sunlight, water, and wind (or storms), the various canopies affect the organisms living nearer the forest floor differently. For example, the canopy of coniferous forests filters light through narrow leaves, allowing organisms living in the canopy and below to receive small amounts of direct sunlight. Broadleaf tree canopies, by contrast, block the sunlight and provide a dark and moist environment below.

In addition to filtering sunlight and performing photosynthesis, the forest canopy provides five services to the environment: nutrient delivery to the soil in the form of biomass, when leaves and small branches fall to the forest floor; soil erosion reduction by protecting the ground from heavy rainfalls; particle and pollutant removal from the air, rain, and fog; transpiration in the water cycle; and habitat for animal and plant life that exist only in this place. The canopy habitat is so specialized, in fact, that it makes up what is known as a microhabitat. A microhabitat is an area within a larger habitat that has unique characteristics found nowhere else in the environment.

Plants that live only in the forest canopy are epiphytic plants, meaning they receive physical support from the canopy and not by putting roots into soil, and they draw water and nutrients directly from the atmosphere. Epiphytes contain about 30,000 species, including Spanish moss, lichens, liverworts, ferns, cacti, vines, and up to 70 percent of all orchids.

The canopy’s animal life is also unusual because the canopy includes species that rarely if ever visit the ground. A wide variety of flying and crawling insects, including bark-eating and wood-boring insects and spiders, mites, centipedes, and millipedes, live in the canopy. Invertebrates such as worms, snails, and slugs also live as either carnivores or herbivores in addition to the reptiles and amphibians that are found there. Songbirds and woodpeckers spend entire lifetimes in the canopy, and raptors such as hawks and owls hunt from the canopy. Some 90 percent of all tropical rain forest organisms stay in the canopy their entire lives.

Warm-blooded life in the canopies of the world, especially in tropical rain forests, is the most diverse on Earth. Monkeys and lemurs have prehensile tails that enable them to grab branches, while other animals evolved as gliders to travel through the forest’s upper reaches. Flying squirrels, colugos, Draco lizards, and flying frogs possess a body form that catches the air and helps them glide from branch to branch. The slowmoving sloth also lives exclusively in the tropical rain forest canopy by clinging to tree trunks with sharp claws.

Urban areas have started taking a cue from nature by planting trees in treeless neighborhoods, partly because of the benefits of the canopy. Urban tree canopies help reduce city carbon dioxide levels and pollutants, absorb storm water, provide shade to decrease the use of air conditioners, and reduce traffic noise. Very often, trees in the city increase property values. Said Kelly Quirke, head of Friends of the Urban Forest in San Francisco, California, “As more of us live in cities and as we lose more open space, people are getting more and more of their experience in nature in their urban environment. That means the urban forest becomes ever more critical.” An urban forest can never replace the unbroken expanses of forestland that existed before towns grew up, but they make their own contribution to returning some habitat to large metropolitan centers.

Source of Information : Green Technology Conservation Protecting Our Plant Resources

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