GE2201 : Terrestrial Environments

Sunday, March 12, 2006

Tropical Rainforest

These forests, which are responsible for the production of 40% of the earth’s oxygen, now cover only 2% of the earth’s surface amazing considering they are home to more than half the world’s flora and fauna. The trees here are not made up of pure stands, unlike temperate coniferous forests which are mainly made up of patches of forests with only one particular species of tree. Because of this tropical rainforests support the most diverse ecosystems of the world’s biomes.
Precipitation is among the highest, with annual rainfall above 2m, reaching 2.5m during the monsoon, and annual temperatures are slightly above 25C. Temperatures dip to 10-15C at night. Because of these stable conditions the vegetation is relatively dense.Compared with the temperate coniferous forests further away from the equator, where annual temperatures range from 21C to -1C. Because of its location, it receives much sunlight all year round and hence the never-ending growing season. Because of the dense canopy there are minimal winds passing through and most of the plants within the forest depend either on explosive action or animals to disperse their seeds.
Adaptations of the flora include the barks of trees. Bark, a tree’s outer covering, is essential to trees in the colder regions. Here, in a humid environment, the treebarks are mostly thin and branchless. Branches are unnecessary because of the dense uppercanopy, and thin bark is adopted because of the temperature, unlike the other colder forests where the trees have thick strong bark to protect them from water loss and low temperatures. Also, in order to protect themselves against the climbing plants, epiphytes and plant parasites, the barks are smooth.
The soil quality is commonly thought to be very fertile in order to support all this life, but in actual fact it is poor in nutrients because the heavy rain has washed most of it away.
The most distinctive feature is the five-layered structure; the emergents, canopy, undercanopy, shrub layer and undergrowth. The emergents consist of those trees that have umbrella- shaped canopies and shallow root systems, which they make up for with buttress roots that may protrude 3m aboveground and spread out 10m. The canopy is around 30m, and is the densest of all the layers. All the tree crowns may interlock over the bottom layers, and block out 90% of the sunlight. There is food in abundance here, so animals living here do not bother going down to scourge for food. The undercanopy is made up of trees growing up to 20m, and the shrub layer consists of shrubs and small trees which have leaves that point upwards to catch falling leaves and maximize surface area for sunlight absorption. The lowest layer, the shrub layer, is composed of minimal plant growth because less than 1% of the sunlight from up there manages to penetrate through. The fallen litter here is quickly broken down by decomposers such as earthworms, fungi and other plants.

8:32 AM

.tts all folks.