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Natural Vegetation1

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Hosea Leow

on 5 February 2013

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Transcript of Natural Vegetation1

Natural Vegetation Whole community of plant life that exists without any form of human modification Types of Forests Global Distribution of Natural Vegetation Influence of Climate on Vegetation Precipitation Temperature Coniferous Forests Tropical Monsoon Forests Tropical Mangrove Forests Tropical Rainforests Forests Deserts Grasslands Main Types of Natural Vegetation - Consists of mainly trees
- generally has many varieties of plants - Consists mainly of grasses
- has few varieties of plants - Consists of mainly sparse vegetation, such as scrubs and tough grasses in the hot desert and mosses and lichens in the cold
- has very few varieties of plants Distribution: Describe the relationship between climate and vegetation types. The total annual amount of rainfall and its seasonal distribution determines the main types and density of vegetation. As plants need heat and warmth to grow, temperature conditions are critical in influencing the world’s distribution of vegetation. Temperature will help to determine the sub-types. (b)Moderate annual rainfall of between 250mm and 1000mm with alternate dry and wet seasons will give rise to grassland, e.g. tropical grassland (savanna) and temperate grassland (steppe). (a)High annual rainfall of 1000mm to more than 2000mm, well-distributed throughout the year, will support forest, e.g. tropical rainforest and temperate forest. (c)Low annual rainfall of less than 250mm can only support desert vegetation, e.g. hot desert and tundra. (a)High average annual temperatures of above 20 deg. celsius (usually in the Tropical climatic zone), the growth of plants, usually trees, is abundant. (b)Moderate average temperatures ranging from 6 deg. celsius to less than 20 deg. celsius(usually in the Temperate climatic zone), depending on seasons, temperate vegetation such as temperate deciduous forest or temperate grassland will survive. (c)Low average temperatures of less than 6 deg. celsius, where there is little or no plant growth as most plants cannot grow where temperatures fall below 6 deg. celsius. In places where temperatures are below 0 deg. celsius (usually in the Polar climatic zone), only plants like mosses and lichens can grow there as they are able to adapt to the very low temperature. Distribution of world’s major natural vegetation Distribution:
latitudes
- mainly in the tropical region between 10 N and S of the Equator.
climate
- Tropical Equatorial Climate
- high temperature of about 27 C
- total annual rainfall over 1500mm, uniformly distributed throughout the year
e.g. of places
- Amazon Basin in South America, Congo Basin in Africa, Southeast Asia such as Indonesia, Malaysia & Singapore Structure:
5 vertical layers Forest Floor (0-5m):
a.k.a. 'undergrowth layer'
made up of mainly grasses, ferns, mosses & fungi
sparse vegetation due to very little sunlight
leaf litter (decomposes quickly to form humus due to the high temperature & rainfall) Shrub layer (5-6m):
tree saplings and woody plants Understorey layer (6-15m):
Young trees
trees have narrower, oval-shaped crowns
grow where gaps in canopy allow sunlight to pass through
Lianas (thick woody vines), epiphytes (bird's nest ferns, orchids) are found here
parasitic plants (strangling fig) are also found here Canopy layer (15-30m):
wide, shallow & umbrella-shaped crowns form a continuous leaf cover, called a canopy
prevents sunlight from penetrating into the lower layers of the forest
Lianas (thick woody vines), epiphytes (bird's nest ferns, orchids) are found here
parasitic plants (strangling fig) are also found here Emergent layer (30-50m):
crowns of very tall trees, called emergents
these trees need more sunlight to grow
these trees have very tall, thick, straight trunks Density:
extremely dense due to the high temperature & high rainfall, as such climate encourages faster germination and abundant vegetation growth Diversity:
a large variety of plants, due to the high temperature & high rainfall all year round
contains more than 750 species of trees & 1500 species of other plants in every hectare Leaves:
TRF are evergreen (do not shed leaves at the same time) due to the high temperature & high rainfall all year round
Broad, waxy to reduce loss of water through transpiration as temperature is high throughout the year
drip-tips to allow water to drain off easily so as to prevent accumulation of water on the leaves as high temperatures & high rainfall promote the growth of bacteria Flowers & Fruits:
flower & produce fruits throughout the year
flowers are colourful & fruits are sweet-smelling to attract insects & birds to help in pollination (due to the high temperature & high rainfall that contributes to the dense vegetation with thick canopy, air is still and plants cannot depend on wind for dispersion) Barks & Branches:
smooth & thin bark as there is no need for protection against cold or extreme dry weather (due to the fact that high temperature & high rainfall is experienced)
branches are found on the top one-third of the tree trunk so as to obtain maximum light for photosynthesis (the vegetation is dense due to the high temperature & high rainfall, thus little sunlight can penetrate through the thick canopy) Roots:
shallow roots as there is no need to reach deep into the soil for water & nutrients
- much moisture is found on the forest floor due to the high rainfall received
- nutrients are also found on the top layer of soil as the high temperature & rainfall all year round cause the leaf litter to decompose and form humus rapidly
buttress roots to support the heavy weight of the tall trees latitudes
- mainly in the tropical region between 10 & 25 N and 10 & 25 S of the Equator.
climate
- Tropical Monsoon Climate
- high temperature of about 26 C
- total annual rainfall over 1500mm
- Distinct wet & dry season
e.g. of places
- South Asia, Southeast Asia, Southern China and Northern Australia Distribution: Structure:
3 vertical layers ground layer (0-6m):
a.k.a. 'undergrowth layer'
made up of mainly shrubs and undergrowth
slightly denser than tropical equatorial rainforests (due to more open canopy) Understorey layer (6-15m):
made up of mainly shorter trees, woody shrubs Canopy layer (15-30m)
Continuous leaf cover with opening
More open than Tropical Equatorial Rainforest
Creepers, vines, epiphytes, parasitic plants are also found in this layer Density: Dense vegetation due to the high temperature and high rainfall (but less dense than Tropical Equatorial Rainforest) Diversity: 200 species in every 1 hectare Leaves: Monsoon forests are deciduous (shed leaves during dry seasons to reduce water loss) due to the high temperature & low rainfall during the dry seasons
Broad & leathery to reduce loss of water through transpiration as temperature is high throughout the year
drip-tips to allow water to drain off easily so as to prevent accumulation of water on the leaves as high temperatures & high rainfall promote the growth of bacteria Flowers & Fruits: Bears flowers & fruits during dry seasons (when trees are leafless) Barks & Branches: thick & coarse barks (to protect them from forest fires, especially during dry spells) as high temperatures are experienced throughout the year
branches are found growing from 1/2 way of the trunks Roots: deep long roots (to tap underground water during the dry seasons) as temperature is high all year round and rainfall is low during the dry seasons More tolerant to brackish water Less tolerant to brackish water Diversity:
Halophytes
(Salt-tolerant plants) latitudes
- mainly in the tropical region between 23.5 N & S of the Equator, along sheltered coastal regions & rivers where clay and silt is constantly deposited
climate
- Tropical Climate
- high temperature of about 20 C to 30 C
- total annual rainfall of 1000 to 2000mm
e.g. of places
- tropical African coastland such as West Africa (Nigeria and Senegal) and eastern Africa (Tanzania, Mozambique & Madagascar)
- swampy coastal areas of Southeast Asia (Indonesia, Malaysia, Singapore)
- coastal districts of tropical Brazil, Venezuela, and the Guianas
- northern Australia, southern peninsular India & Sri Lanka Distribution: 3 distinct horizontal/lateral layers
lined according to its tolerance to the salt water
height of about 10-15m Structure: Dense & luxuriant growth due to the high temperatures and rainfall Density: Thick, leathery leaves to reduce water loss through transpiration due to high temperatures
Leaves are broad & have drip-tips to allow water to flow off quickly due to the high rainfall
Salt secretors (Avicennia) secrete excess salt on their leaves, which are then removed by wind or rain
Ultrafiltrators (Bruguiera, Rhizophora & Sonneratia) absorb salt and remove the excess by storing in old leaves which then fall off Leaves: Aerial Roots (grow above soil to get air as waterlogged soil is not well aerated
Stilt/Prop roots (Rhizophora) or kneed roots (Bruguiera) to anchor firmly/ have firm support in the soft muddy soil Roots: Flowers are generally colourful to attract insects to pollinate the flowers
Fruits are buoyant & can stay afloat till they find coastal location where they take root (Avicennia & Sonneratia)
Fruits germinate in parent plants and are elongated with sharp tips which allow them to anchor in soft muddy soil and sprout once they fall off from parent plants (Bruguiera & Rhizophora) Flowers & Fruits: Brackish Water
(salt in water) latitudes
- mainly in the temperate regions between 60 N & 70 N of the Equator
climate
- Cool Temperate Climate
- experiences seasons - summer temperatures averaging 21 C & winter temperatures as low as -40 C
- low total annual precipitation of about 300mm to 635mm, mainly in the form of snow
e.g. of places
- Alaska, northern Canada, northern USA, Scandinavia (Finland, Norway, Sweden) and Russia Structure: No distinct layers
Generally uniform height of about 20-30m Not dense as low temperatures & precipitation Density: Few species (common species: fir, spruce, pine)
Tend to grow in pure stands Diversity: Evergreen conifers
-Do not shed leaves all at one go
-Retain leaves to photosynthesise and make food whenever temperature rises above 6°C
Needle-like/ twig-like leaves to reduce water loss through transpiration due to dry conditions, especially during winter when ground is frozen Leaves: Thick barks to protect from cold winters, and help to store food & conserve moisture for the dry cold seasons
Flexible branches that point downwards to allow snow to slide off easily & prevent accumulation of snow whose weight could break the branches Barks & Branches: Shallow roots to facilitate intake of nutrients & water on surface when the snow melts Roots: -Seeds are contained in cones to survive cold & dry conditions
-Cones can be male or female (female produce seeds while male produce pollen) Flowers & Fruits:
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