CHAPTER 11
FORESTS
Forests are the lungs of the earth but only 6% of the planet's surface is covered by forests
whereas it houses around 50% of Earth's plant and animal species. Forests support diverse
life forms. A forest provides three ingredients essential for the survival of any living
species: water, food and shelter.
Benefits of Trees:
•
Trees are home to many creatures. Without trees and the forests, our planet would
not be able to support most living things or organisms.
•
More than 90% of all species living on land make their homes in trees and forests.
Without trees and forests, many animal species would become extinct and disappear
forever like the dinosaurs.
•
Trees provide us with many things like timber, fruits, gum, resins etc..
•
When a tree is cut down, it is usually made into lumber, or cut wood for building
homes and furniture.
•
Some trees are pulped or ground up to make paper products such as office paper,
cardboard boxes, magazines and newspapers.
•
Trees release oxygen into the atmosphere and take carbon dioxide, thereby reducing
global warming.
•
Trees help to control soil erosion.
Plant life found in forests is a part of the food chain. The forest is home to many types of
plants that are the food source for many animals. These animals, in turn, are sources of
food for other animals.
The links between all animals and all plants, is often referred to as "the web of life" – a
reference to the interdependence between all life in an ecosystem.
Forest Products in India
1. Timber :- More than 1500 species of trees are commercially used for timber in India.
These are used in timber-based industries such as plywood, saw milling, paper and pulp,
and particle boards.
2. Bamboo:- These are common in the north-eastern and the south-western parts of India.
The main commercial uses of bamboo are as timber substitutes, fodder and raw material
for basket, paper and pulp and other small-scale industries.
3. Cane:- Cane or rattan are the stems of a climber plant and are used to make a large
number of household items. It is used to make walking sticks, polo sticks, baskets, picture
frames, screens and mats.
4. Grasses:- Lemon grass, palm rose grass, bhabbhar, and khus grass are commonly used
grasses.
5. Fruits:- Fruit trees are an important source of income and food for rural areas. Mango,
coconut, orange, pear, jackfruit and many others grow wild in the forest.
6. Medicinal uses:- Even today man is dependent on the forest for herbs and plants to
fight against diseases. Leaves, bark and other parts of many other trees have medicinal
properties and are used to make various ayurvedic medicines e.g. Neem.
7. Fibre:- Plant fibre has many different uses. Soft fibres such as jute are derived from the
stems of the plant. Hard fibre from the leaves of hemp and sisal are used to make fabric.
Coir, another form of fibre from the fruit of the coconut, is used to make rope.
8. Floss:- The fruits of many species of Indian trees produce silky floss. The most common
of these is simal. It is used to make cotton wool, mattresses and pillows.
9. Essential oils:- Tropical grasses such as lemon grass, citronella and khus are the source
of Essential oils. Oil is distilled from the wood of various species such as sandal wood, agar
and pine. Oil is also derived from the leaves of certain plants and trees such as eucalyptus,
camphor, wintergreen and pine. These oils are used for making soaps, cosmetics, incense,
pharmaceuticals and confectionery.
TYPES OF FORESTS
The types of trees that grow in an area depend on the location and climate. Climate varies
so much across the world that there are six different kinds of forests on earth.
Coniferous Forests
A coniferous forest is made up of coniferous trees that can survive in an extreme
environment. The vegetation consists of mostly evergreen trees, which are trees that grow
needles instead of leaves and cones instead of flowers. E.g. pine, spruce, fir. They are
located in Canada, Europe and USA. Coniferous forests are found in areas with
temperatures between -40degrees and 20 degrees C and rainfall between 300 and 900 mm
per year.
Temperate Forests
Temperate forests grow in regions that have four separate seasons: winter, spring, summer
and autumn. They also thrive in areas where there is enough rainfall to support the trees
and other plants.
Temperate forests have two kinds of trees:
1.
Deciduous trees:- These trees have broad leaves and shed their leaves during
autumn.
2.
Evergreen or coniferous tree:- These trees remain green throughout the year and
have
needle-like leaves and cones.
They are located in Canada, Asia, Europe and Eastern United States. They are found in
areas that have temperatures between -30 degrees and 30 degrees C and rainfall between
750-1500 mm per year.
Tropical Rainforests
Tropical rainforests only contain trees and plants that require warmth and lots of water.
The vegetation consists of vines and palm trees. Rainforests are so dense with vegetation
that they provide much of the world‘s oxygen. They also contain half of the known species
of animals and plants on earth.
We find tropical rainforests in Africa, Asia, Australia and Central and South America. It
receives rainfall between 2,000 and 10,000 mm per year. It rains all year round.
Mountain Forests
Mountain forests grow in very high altitudes or on mountain tops. They can thrive
anywhere in the world. Because they are so high, mountain forests are home to plants and
animals that can survive in intense sunlight and a cold, wet climate.
Conifers are the most common trees found in mountain forests.
Mediterranean Forests
Mediterranean forests are so named because they are near the coasts of the Mediterranean
Sea. Most of the trees in a Mediterranean forest are evergreens .These forests also grow in
areas that have Mediterranean-like climates, such as California and Western Australia.
AFORESTATION & DEFORESTATION
In order to maintain proper ecological balance a certain percentage of the total land area of
any country should have forest cover. If this is reduced, it results in both floods and
famine. In aforestation programmes, forest trees are planted in suitable areas and also on
waste land. Exotic and fast growing tree species which do not disturb the ecological
balance are planted. Aforestation is the process of establishing a forest by planting trees on
land that is not a forest. Aforestation is the opposite of deforestation. Deforestation is the
clearing of forest.
Benefits of Aforestation
•
Preserves wildlife- Planting of trees enables the wild animals to live in their natural
environment freely, thereby helping in maintaining ecological balance.
•
Tourist attraction- Eco tourism is being encouraged worldwide to enable tourists to
view animals in their natural environment.
•
Minimises soil erosion- Soil erosion is significantly reduced as tree plantations
prevent run off of soil after heavy rains.
•
Provides forest products
•
Stabilises the climate-Planting of trees in semi-dry areas attracts rainfall and
prevents these areas from becoming deserts. This also enables irrigation to be carried
out efficiently.
•
Aforestation provides employment for tree planters.
Deforestation
Deforestation is the removal of a forest after which the land is converted to a non-forest use
e.g. to farms, ranches, or urban use. Deforestation refers to the cutting, clearing, and
removal of forest.
The main causes of deforestation are logging, mining, oil and gas extraction, making
ranches for cattle and agriculture. The poor soils in some parts of the world do not support
agriculture for long. Thus, people are often forced to move on and clear more forests in
order to maintain production.
Consequences of Deforestation
• Soil erosion: loss of the protective vegetation cover that binds the soil with its roots
leads to more soil being lost.
•
Silting of water courses, lakes and dams: occurs as a result of soil erosion,
•
Extinction of Species: more than half of all species on our planet live in forests and
deforestation destroys their habitat.
•
Desertification: Deforestation is one of the contributing factors for desertification.
EXERCISES
A. Read the statements given below. Write whether true or false
a) Tropical rainforests are known for their heavy rainfall and cool air.
_________
b) Only wood and food products are produced in forests.
_________
c) Cloud forests get their water from the moist air of lower areas.
_________
d) Trees cannot grow at the earth‘s poles.
_________
e) Deciduous trees sometimes grow in the same forests as conifer trees.
_________
f) A tropical rainforest needs four seasons to thrive.
_________
g) Mediterranean forests can only grow near the Mediterranean Sea.
_________
h) North America is home to Temperate and Mediterranean forests.
_________
i) A coniferous forest can live with very little rainfall.
_________
j) Deciduous trees produce cones to carry seeds.
B. Answer the following questions in brief.
_________
List 10 items that come from trees or that are made from tree by-products. Include a few
unusual/uncommon plant products.
a) __________________________
f) __________________________
b) __________________________
g) __________________________
c) __________________________
h) __________________________
d) __________________________
i) __________________________
e) __________________________
j) __________________________
C. Identify the various characteristics given below according to the type of forest and
write them under the headings given in the table accordingly.
CHARACTERISTICS
1.
-40 C to 20C
2.
300mm to 900 mm rainfall
TYPE OF FOREST
3. Trees with needles
4. 2000mm to 10000mm rainfall
D. Imagine you are a forest ranger. Write your diary for 'A day in the forest.'
CHAPTER 12
SOILS
What is Soil?
Most of the land in the world is covered with soil. Soil is a major
part of the natural environment and is vital to the existence of life on
the planet.
Soil is the result of the process of the gradual breakdown of rocks that
makes up the earth. As rock break down through a variety of processes,
such as weathering and erosion, the particles become smaller and smaller. The four main
components of soil are: Pieces of finely ground rock, humus (humus is made up of little bits
of decayed leaves and tiny pieces of rotting wood, seeds and decayed plants and animals),
water and air.
How is soil formed?
Both top soil and subsoil are made up of rock ground down over many years by rain,
running water, frost, heat and wind. This process is called erosion. Soil is formed through
erosion. Soil is different in different parts of country and the world. This is because the
rocks and organic matter that make up the soil are different everywhere.
The Four Layers of Soil
The uppermost layer of the soil is called topsoil.
It is the darkest of all layers. The dark color is due to
the presence of humus which makes the soil fertile.
This layer contains roots of many plants which absorb
water and nutrients from it. Soil is soft and porous
with great capacity to hold water. The topsoil is home
to many organisms like bacteria, algae, fungi, insects
and worms.
The layer of soil below the top soil is called subsoil.
Subsoil is harder and more compact than the topsoil.
It does not contain humus and is therefore, lighter in
colour than the topsoil. B-Horizon is rich in soluble
minerals and iron oxides. Roots of certain tall trees
reach up to this layer.
The layer below the sub soil consists of small pieces of the parent rock. Weathering of these
pieces of rock result in soil formation. The rock pieces contain many cracks and crevices.
Although no organic matter (humus) is present in this layer, it contains some minerals. This
layer is known as the weathered or decomposed rock.
Beneath this layer is present the solid parent rock called the bedrock. It is made up of the
parent rock. It is difficult to dig beyond this layer normally.
Why soil is different at different places?
Soil is formed by the weathering of the local rocks. There are two reasons why soils are
different in different places:
1) Different Climates:
The wetter climates favour chemical weathering, which breaks down minerals into
different compounds, and the growth of plants, so soils have lots of clay and organic
materials. Dry climates favour mechanical weathering that breaks the rocks into small
particles, so soils in this climate have lots of sand and silt and little organic material.
2) Parent Material:
The natural rock types in the area have a strong influence on the soils. If the rocks have a
lot of calcium then that will show up in the soils. Some rocks weather easily and form deep
soils and others are very resistant to weather and usually have only shallow soils on top.
Types of soil
a. Sandy Soil :- Sandy soil contains about 60% of sand particles with small amounts of silt
and clay. It is very porous and its water-holding capacity is very low as all the water easily
runs down through the large pores. This type of soil is, therefore, not good for the growth
of plants. Sandy soil is found mainly in the deserts.
b. Clayey Soil:- Clayey soil contains more than 50% of clay particles. Since the clay
particles are very small in size, they are very tightly packed and do not allow water to
drain out easily. Clayey soil, therefore, gets easily water-logged. It is poorly aerated
because the tightly bound clay particles leave little space in between to trap air. Clayey soil
is very sticky and thus tilling the soil is very difficult. However, clayey soil is rich in a
mineral which makes it suitable for plant growth. Due to the great binding capacity of its
particles, clayey soil is used for making toys and pots.
c. Loamy Soil:- Loamy soil contains 30-50% of silt, 5-20% of clay and the rest is sand. It also
contains humus. It has good holding capacity and sufficient space between its particles to
trap air. Therefore, loamy soil is best suited for plant growth.
Soil Erosion
The removal of land surface by water, wind or ice is known as erosion. Plant roots firmly
bind the soil. In the absence of plants, soil becomes loose. So it can be moved by wind and
flowing water. Soil erosion is the removalof soil by the physical movement of soil particles
from a given site. It is a natural process which usually does not cause any major problems.
It becomes a problem when human activity causes it to occur much faster than under
normal conditions.
Causes of Soil Erosion
Erosion occurs when suitable farming practices are not followed. These practices are:
•
Removing the vegetative covering of an area through deforestation and fire.
•
Overstocking and overgrazing.
•
Inappropriate farming techniques such as deep ploughing land 2 or 3 times a year to
produce annual crops.
•
Lack of crop rotation.
•
Over cultivation and compaction which make the soil loose and hence, easily
eroded.
Soil erosion is common in areas with steep slopes, where trees have been cut down, in
droughts when crops and other vegetation grow poorly and in rural areas which are
overpopulated. Places like Nepal, in the Himalayan Mountains, have severe problems
caused by increased population density and steep slopes.
Types of Soil Erosion
Water Erosion:- Water erosion mostly happens due to rainfall intensity. Both rainfall and
runoff of water help in soil erosion. The impact of raindrops on the soil surface can break
down lumps of soil and disperse it. Lighter parts of the soil such as very fine sand, silt, clay
and organic matter can be easily removed by the raindrop splash and runoff water while
greater raindrop energy or runoff amounts might be required to move the larger sand and
gravel particles.
Wind Erosion:- Wind erosion occurs when the land surface is left bare in regions that are
dry enough, as a result of low rainfall, to allow the soil to dry out, and flat enough to allow
the wind to carry the soil away.
Erosion by Gravity:- Due to gravity of the earth the soil gets displaced from one place to
another. This is commonly noticed in hills and mountains.
Preventing Soil Erosion
Some of the following measures that can be implemented to prevent soil erosion:
• Leave unploughed grass strips between ploughed lands (strip cropping).
•
Make sure that there are always plants growing on the soil, and that the soil is rich
in humus.
•
Avoid overgrazing.
•
Allow native plants to grow along riverbanks.
•
Conserve wetlands –a wetland is a land area that is saturated with water
permanently or seasonally. The water either covers the soil or is present near the
surface of soil all year.
•
Cultivate land using a crop rotation system, i.e., growing of different crops in the
fields each year so that soil nutrients do not become exhausted.
•
Minimum or no tillage (preparing the land for growing crops).
•
Encourage water infiltration and reduce water runoff from the slopes or fields.
EXERCISES
Q1. Answer the following questions:a:- Thousands of tiny creatures live in soil‖. Name three of them.
Ans.:_________________________________________________________________________________
_________________________________________________________________________________
_________________________________________________________________________________
b.:- What is the effect of soil erosion on plants?
Ans.:_________________________________________________________________________________
_________________________________________________________________________________
_________________________________________________________________________________
C.:- Name three kinds of soil erosion. Explain each one.
Ans.:1)___________________________________________________________________________
_________________________________________________________________________________
_________________________________________________________________________________
2)
_________________________________________________________________________________
_________________________________________________________________________________
________________________________________________________________________________
3)
_________________________________________________________________________________
_________________________________________________________________________________
_________________________________________________________________________________
Q.3:--Paste pictures of two kinds of soils.
RESEARCH WORK
Q.4:- Which type of soil is useful for cultivating the following:
a) Rubber: ______________________________
b) Cactus: _______________________________
c) Rice: _________________________________
d) Coco:_________________________________
e) Cotton:________________________________