Tropical rainforest

Amazon river rain forest in Brazil

A tropical rainforest is a rainforest with tropical animals and plants. They are found in a band around the equator and cover 6% of the Earth's surface. They are warm for most of the year but have a lot of rainfall. They also have many different plants and animals. The tropical rainforest is a biome. The biggest tropical rainforest is mostly in Brazil. Other rainforests are in Asia (Indonesia mainly), central Africa and north eastern Australia. A tropical rainforest gets over 274 cm of rainfall every year.

Characteristics

The characteristics of this type are forest are:

1. Land is mostly under 700 metres down to below sea level
2. Climate:
   1. High rainfall
   2. High temperature
   3. Equable: not much variation
3. Vegetation: 90% or more Angiosperms
   1. Tall canopy trees
   2. Lianas (climbing plants)
   3. Epiphytes
   4. Leaves large, complete margins, with drip tips
   5. Flowers and fruits large
   6. Pollination mainly by insects
   7. Leguminaceae are the most common plant family
   8. Evergreens: leaves may be shed, but not seasonally
4. Animals
   1. High diversity: many different species
   2. Many insects which eat plants, and many anti-insect defences by plants
   3. Many arboreal (tree-living) mammals

History

The Amazon rainforest taken from plane

There is more known of the history of the Amazonian rainforest than any other. The rainforest likely formed during the Eocene era. Flowering plants are first seen in the Lower Cretaceous, and they radiated in the Upper Cretaceous. The evolution of the large forest canopy trees came right at the end of the Cretaceous, when trees like beech, oak, maple, and magnolia are seen. The herbaceous Angiosperms appear even later.

The rain forest has been in existence for at least 55 million years, and most of the region remained free of savanna-type biomes at least until the Pleistocene ice age, when the climate was drier and savanna more widespread.

Following the Cretaceous–Paleogene extinction event, the extinction of the dinosaurs and the wetter climate may have allowed the tropical rainforest to spread out across the continent. From 65–34 mya, the rainforest extended as far south as 45° south. Climate fluctuations during the last 34 million years have allowed savanna regions to expand into the tropics. During the Oligocene, for example, the rainforest spanned a relatively narrow band that lay mostly above 15° north. It expanded again during the Miocene, then retracted to a mostly inland formation at the last glacial maximum (roughly 25 to 20,000 years ago). However, the rainforest still managed to thrive during these glacial periods, allowing for the survival and evolution of a broad diversity of species.