www.soran.edu.iq Ecology M. Saadatian Biomes 1
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Distribution of biome
• The tropical rainforest is found between 10 ° N and 10 ° S latitude at elevations below 1,000 m. There are three major, disjunct formations:
• Neotropical (Amazonia into Central America) • African (Zaire Basin with an outlier in West Africa;
also eastern Madagascar) • Indo- Malaysian (west coast of India, Assam,
southeast Asia, New Guinea and Queensland, Australia.
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Climate
• The tropical rainforest is a forest of tall trees in a region of year-round warmth. An average of 1250 to 6600 mm of rain falls yearly.
• The temperature in a rainforest rarely gets higher than 34 °C or drops below 20 °C; average humidity is between 77 and 88%. There is usually a brief season of less rain. In monsoonal areas, there is a real dry season. Almost all rainforests lie near the equator.
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Soil• The soil is infertile, deeply
weathered and severely leached. Rapid bacterial decay prevents the accumulation of humus. The concentration of iron and aluminium oxides gives the soil a bright red colour and sometimes produces minable deposits (e.g., bauxite). On younger substrates, especially of volcanic origin, tropical soils may be quite fertile.
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Plants I• A tropical rainforest
has more kinds of trees than any other area in the world. Scientists have counted about 100 to 300 species in one 1-hectare area in South America. Seventy percent of the plants in the rainforest are trees.
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Plants II• All tropical rainforests resemble one another in
some ways. Many of the trees have straight trunks that don't branch out for 100 feet or more. There is no sense in growing branches below the canopy where there is little light. The majority of the trees have smooth, thin bark because there is no need to protect them from water loss and freezing temperatures. It also makes it difficult for epiphytes and plant parasites to get a hold on the trunks. The bark of different species is so similar that it is difficult to identify a tree by its bark. Many trees can only be identified by their flowers.
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Carnivorous plants
Pitcher plant or Monkey Cup
Venus Fly Trap
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Plants III (growth forms)• Epiphytes: the so-
called air plants grow on branches high in the trees, using the limbs merely for support and extracting moisture from the air and trapping the constant leaf-fall and wind-blown dust.
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Plants IV (growth forms)
• Lianas: woody vines grow rapidly up the tree trunks when there is a temporary gap in the canopy and flower and fruit in the tree tops.
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Plants V (growth forms)• Climbers: green-
stemmed plants that remain in the understory. Many climbers, including the ancestors of the domesticated yams (Africa) and sweet potatoes (South America), store nutrients in roots and tubers.
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Plants VI (growth forms)
• Stranglers: these plants begin life as epiphytes in the canopy and send their roots downward to the forest floor.
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Fungi• Fungi can live on the forest floor because they do
not need sunlight for growth.
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Plants VIII
• Rainforests now cover less than 6% of Earth's land surface. Scientists estimate that more than half of all the world's plant and animal species live in tropical rainforests. Tropical rainforests produce 40% of Earth's oxygen.
• About 1/4 of all the medicines we use come from rainforest plants. More than 1,400 varieties of tropical plants are thought to be potential cures for cancer.
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Animals• Animal life is highly diverse. Common
characteristics found among mammals and birds (and reptiles and amphibians, too) include adaptations to an arboreal life (for example, the long tails of New World monkeys), bright colours and sharp patterns, loud vocalizations, and diets heavy on fruits.
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Tree frogs
Constrictor Python
Chameleon
Amphibians and reptiles
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People II• Farming: huge tracts of rainforest are cleared for
large-scale commercial plantations or livestock ranching. Ironically, rainforest soil is useless to humans. Rainforest soils are notoriously poor and cannot support human agriculture for more than a few years. Crops may grow well at first, mostly subsisting on the minerals released when the forest is burnt. But these minerals wash away quickly without the protection of the thick forest canopy and the soil soon becomes useless.
• Humans destroy by collecting and killing wild animals and plants.
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People III• Rainforest is also cleared to make way for homes
for people, and infrastructure like dams, roads, electrical and communications installations.
• Rainforests are dug up as we mine for oil, gold and other minerals. Small scale gold prospectors use mercury which is toxic to extract gold.
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People IV• Logging of trees for building materials, firewood,
paper products. Rainforests contain 50% of global standing timber. Unlike the faster-growing temperate timber trees, rainforest trees take decades to reach economic size so it is not easy to harvest them in a sustainable manner. Logging roads usually allow other commercial exploitation to follow.
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People V• Humans kill by breaking up a rainforest into smaller
clumps. It destabilises the forest interior: temperature and humidity are no longer constant. Such fluctuations kill plants and animals adapted only for stable conditions. If the fragment is too small, it can't withstand natural seasonal changes. It also prevents natural movement of plants and animals from one part of the forest to another.
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Temperature
•Temperatures are high all year: the average temperature is above 24°C
•Because of its proximity to the coast, fluctuations in annual temperatures are only 10-15° C
•Frost and temperatures below freezing are rare
•Temps. have been recorded as low as 3°C and as high as 31°C
• The air changes from moist due to inter-tropical region mixtures in the summer to the dry air because of a subtropical weather front during the winter
Imperative Information
Solar Isolation
• Seasonal alternation
•A well defined dry season, but a short wet season in comparison to a tropical rain forest
•The dry season typically lasts from June through August
Precipitation
•The dry season is far longer than the brief period of rainfall
•There is no set amount of rain, it depends on the area
•Annual rainfall is anywhere from 10-20 cm to 1000 – 1500 cm per year depending on the specific tropical dry forest
•There is decreasing summer precipitation
Limiting Factors
•Its well defined dry season limits plant growth and the activity of animals
•A large soil-water shortage occurs, especially severe during the hottest time prior to the rains
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Species Diversity
Plant Life• Most of the trees and shrubs found in this
type of habitat are deciduous, losing their leaves at beginning of the dry season – Leaves shed in dry season to conserve soil
moisture.
• Up to 40 tree species in small forests• Dry forests consist of trees, shrubs, and
undergrowth of different heights which form a canopy
• Lotus, ironwood, and acacias • Columnar, jumping cholla and barrel cactus • More light penetration and more understory
vegetation than a tropical rain forest
Animal Life• Tasmanian devil • American alligator• Merriam's Kangaroo rat • Ants• Lizards• Shrews • Coyotes • Kit and gray foxes• Ringtails• Raccoons• Skunks • Badger • Bobcat • Mountain lion • Ocelot
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Food Chain
Energy from sun
First tropic level: Producers
Second tropic level: Primary consumers
Third tropic level: Secondary consumers
Fourth tropic level: Tertiary consumers
Decomposers
heatheat heat heat
heat
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Climate / Seasons: Tropical dry forests have a seasonal climate, alternating between a wet and dry season. However, the dry season is often longer than the wet season, lasting over five months every year. Temperature:
The annual mean temperature is approximately 81ºF, or around 27ºC. However, in the dry season, this may increase to 99ºF, or 37ºC.
Geography: Located from 10º to 25º N and S.
Precipitation: The annual rainfall is usually around 150-200 cm.
Soil: The soil in this area is richer with nutrients, but is more vulnerable to erosion.
Limiting Factors of the Biome: The fact that the dry season lasts longer than the wet season, as well as the soil’s high susceptibility to erosion, limits the growth of certain plant life. This, in turn, will limit the biome’s ability to sustain animal life.
Sunlight: Trees are not as close to each other as in a rain forest, therefore allowing more sunlight to reach the forest floor.
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