Course: Biogeography

Date: March 5, 2013

TROPICAL RAINFOREST

A rainforest is a thick forest in moderately warm to very hot areas which have heavy rainfall and high humidity .

Definition………

Location of Tropical Rainforest

Tropical Rainforests are found between 5- 10 degrees north and south of the equator. Some countries /areas that Tropical forest biomes are found:

Brazil IndonesiaMalaysiaMadagascarParts of AustraliaThailandAmazon Basin Congo

Where is it ………?

CLIMATEHigh annual

temperature (27- 30 degree)

Temperature is uniformHigh humidity and

cloud cover. no dry season.Mostly convectional

rainfall.Average rainfall is

between 1,200mm to 3000mm per year.

SoilLatosols or ferralitic soilsExtensive chemical weathering resulting

from the high rainfall and temperature leads to the development of deep soils, often 20m to 30m deep

The soils have a loose structure and are rapidly eroded once the protective layer of vegetation is removed

Except for the top few inches, soil fertility is poor

Thick litter layer

Thin dark humus layer

Many soil organisms mix soil

well

Oxides of iron and aluminium stain soil

red

Hydrated oxides produces red/yellow

colouration

Clays produced by intense chemical

weathering

Bedrock

A and B horizons

C horizon

Heavy leaching of silica and bases due to high precipitation

Throughflow of soil water leads to loss of nutrients

Soil depth can reach 30m (100 feet)

A typical latosol profile

VEGETATION

EMERGENT…..Emergent Layer – a

few tree species grow very tall and emerge up through the canopy. These may be 150 feet tall.

The emergent layer is made up of the tallest trees that grow larger than any of the other trees.

It is good to have your leaves in the emergent layer because there is lots of sunlight.

CANOPYCanopy Layer – tall

trees for this dense layer that absorbs most of the light energy. 80 to 100 feet tall. The canopy layer is where most of the leaves in a tropical rainforest are found.

Very dense vegetation

The canopy is very dense, so it blocks out a lot of the light.

The interlocking canopy

UNDERSTOREY Understory or Subcanopy

Layer – made of seedlings that will grow to canopy if light is available and a few shade specialists.

Shorter plants living in the understory of the emergent and canopy layers do not get as much light so they have to be able to grow in the shade.

Only about 1% of the sunlight reaches the understory level.

- Trees are smaller

– Their crowns are not thick

– Most have heights of

between 5m and 15m

UNDERGROWTH/GROUND LAYERConsists mainly of

ferns, shrubs and small young trees.

Covered by a carpet of leaves.

•The forest floor is covered with dead leaves.

•These dead leaves will decompose (rot) and

return the nutrients that they contain to the soil.

The dominant vegetation in Tropical Rainforests is tall, broadleaf, evergreen trees.

Broadleaf = leaves have flat, wide blades instead of needles.

Evergreen = trees maintain foliage (leaves) all year. Deciduous trees, those that drop their leaves seasonally, do so as an adaptation to cold conditions. In the tropics, there is no cold season, therefore there is no need for trees to drop their leaves.

How has the vegetation in tropical rainforests adapted to the climate. Leaves

• Drip tips on the leaves allow excess water to drip off after a downpour

• Leaves are large and smooth with a thin cuticle to facilitate transpiration

• Leaves, especially in the upper canopy have a strong petiole so that the large raindrops do not cause them to break off

LIANASLianas – are vines

that grow up trees to their crown then between the branches of neighboring trees. They “lace” the trees together adding support so they won’t fall over since their roots grow in very shallow soil.

EPIPHYTESEpiphytes – (epi = outer and phyte = plants) – are

plants that grow on other plants. By growing up off the forest floor epiphytes have access to higher quality light (red and blue).

A diversity of plants have adapted to an epiphytic life. There are epiphytic flowering plants, mosses, cacti, ferns, and liverworts.

Many of the trees are covered with epiphytes. The trunks are cloaked in mosses. The large epiphyte in the center is a bromeliad. Large bromeliads like this one are called “tank bromeliads” because their cup of leaves holds a lot of water. That water is the drinking source for arboreal animals. Several species of frogs lay their eggs in it and the tadpoles develop in the treetops.

BUTTRESS ROOTS

Buttress roots are common on Tropical Rainforest Trees. They grow across the surface of the thin rainforest soil. They work like kick stands to keep the tree from tipping over. Also, because the soil is so nutrient poor, deep roots have no need to grow deep. They’re more effective at the surface where they can absorb nutrients from fallen leaves as they decompose.

Slash and burnFireIllegal LoggingAgriculture- cash crop and ranching

PROBLEMS FACED BY THE RAINFOREST

One of the most widely used methods to destroy rainforests is using slash and burn agriculture.� With this type of agriculture, all of the trees and plants in the selected area are uprooted or cut down.� The downed trees and flora are then burnt, so that all of the nutrients in the plants are turned into ash, which is mixed with soil.� After all of the vegetation has been burnt and the ashes have been incorporated into the soil, people plant crops.� The area of land that has been cleared in this manner is only viable for a few years.� Once all of the nutrients have been leached from the soil, the area is abandoned and a new area of rainforest is selected to undergo the same process.

SLASH AND BURN

This type of agriculture is problematic

because�� �The huge number of farmers who have

descended upon the rainforests have placed too much

pressure on the land.� Not enough time is being given

to cleared patches for the forest to regenerate.� This

�slash-and-burn� farming has replaced traditional,

sustainable� cultivation in most tropical forests�

(Lewis,1990, pg 60).� This is very unfortunate because

�slash-and-burn� agriculture is responsible for the ruin

of fifty acres of rainforest every hour� (Gallant,1991, pg

4)

During 1997 several fires broke out worldwide and as a result, �More fires were recorded in that year than at any time in history- millions of hectares of forest were destroyed�� (Gay,2001, pg 32).

 In addition to fires that occur naturally, farmers and native peoples use fire as a tool to clear land for agriculture.� Cattle ranchers also use fire to clear the land for their cattle,��The conversion of the rainforest into grazing for cattle is a genuine ecological catastrophe.� The replacement of the rainforest�s intricate structure by the much simpler structure of pastureland is an intrinsically negative process of biological simplification� (Camarasa,2000, pg 292).

FOREST FIRE…..

Many government agencies are fighting illegal logging to protect the forests. However, any type of logging legal or illegal leads to deforestation. Trees are cut down indiscriminately by logging companies, to fulfill the demands of the wood market. This does not give a chance to the local wildlife and trees to regenerate and sustain themselves. Thus, leading to loss of wildlife forever.Read more at Buzzle: http://www.buzzle.com/articles/causes-and-effects-of-deforestation.html

ILLEGAL LOGGING

Undisturbed and logged rainforest areas are being totally cleared to provide land for food crops, tree plantations or for grazing cattle (Colchester & Lohmann). Much of this produce is exported to rich industrialised countries and in many cases, crops are grown for export while the local populace goes hungry.

Due to the delicate nature of rainforest soil and the destructive nature of present day agricultural practices, the productivity of cash crops grown on rainforest soils declines rapidly after a few years.

Agriculture- Cash Crop and Ranching

Monoculture plantations - those that produce only one species of tree or one type of food - on rainforest soil are examples of non-sustainable agriculture.They are referred to as cash crops because the main reason for their planting is to make money quickly, with little concern about the environmental damage that they are causing.

RANCHING……Cattle ranching has multiple negative effects to both the

environment and the people living in it.� For example, cattle ranching �intensifies deforestation by forcing peasant farmers into the rainforest to seek new land to farm when they are evicted by ranchers who want to convert their farmland to pasture�(Lewis,1990, pg 42).

Cattle ranching is also negative because it� �causes the land to decline in quality as the soil becomes depleted of nutrients.� In fact, land cleared from rainforests generally supports cattle for only three to seven years before it deteriorates beyond recovery� (Lewis, 1990, pg 42).� Just as the farmers do, the ranchers use the land until all the nutrients are gone.� This makes it difficult for new flora to grow back.

One of the factors that allows cattle ranching to destroy rainforests is that �rainforest ranchers have relied on government subsidies and international loans, which make cattle ranching artificially profitable�Rainforest governments have also supported cattle ranching with land giveaways, tax breaks, and free technical assistance. Without this support, rainforest ranching would lose much of its appeal� (Lewis,1990, pg 43)

DEFORESTATION….What is Deforestation?Deforestation is clearing Earth's forests on a

massive scale, often resulting in damage to the quality of the land.

Reference � 

����Colchester and Lohmann (Ed), The struggle for Land and the Fate of the Forest, 1993, Zed Books, London.

Gallant, R. A. (1991). Earth's Vanishing Forests. New York: Macmillan� Publishing Company.

   Gay, K. (2001). Rainforests of the World (2 ed.). Santa Barbara: ABC-CLIO, Inc.    Josep M. Camarasa, R. F. (2000). Encyclopedia of the Biosphere (Vol. 2).

Michigan: The Gale Group.          Lewis, S. (1990). The Rainforest Book. Los Angeles: Living Planet Press.