Chapter: Environmental Science and Engineering


Deforestation means destruction of forests. Deforestation rate is relatively less in temperature countries, but it is very alarming in tropical countries.


Deforestation means destruction of forests.


The total forests area of the world in 1900 was estimated to be 7,000 million hectares which was reduced to 2890 million ha in 1975 fell down to just 2,300 million ha by 2000.


Deforestation rate is relatively less in temperature countries, but it is very alarming in tropical countries.


Deforestation is a continuous process in India where about 3.3 hectares of forest land has been lost. The per capita availability of forest in India is 0.08 hectares per person which is much lower than the world average of 0.8 hectares.


The presence of waste land is a sign of deforestation in India.



1 Causes of Deforestation


Major causes of deforestation are listed below:

Development projects

Shifting cultivation


Fuel requirements cutting and burning

Construction of dams

Growing food needs.



1.1 Consequences of deforestation


Some of the effects of deforestation are listed below:


a) Effect on climate


Global warming Less rainfall Hot climate.


b) Effect on biodiversity


Loss of medicinal plants. Loss of timber, fuel wood.


c)   Effect on resources


Loss of land resource Loss of soil fertility Soil erosion


Drastic changes in biogeochemical cycles


d) Effect on economy


Increase in medicinal values Demand of industrial products. e) Effect on food


Loss of fruit production Loss of root based foods.


Case Studies


Desertification in hilly regions of the Himalayas:


Desertification in Himalayas, involving clearance of natural forests and plantation of monocultures like Pinus roxburghi, Eucalyptus camadulensis etc., have upset the ecosystem by changing various soil and biological properties.


The area is invaded by exotic weeds. These areas are not able to recover and are losing their fertility.


Case Studies


Following the destruction of forest rain fall declined in Chhota Nagpur to such an extent that tea-gardens also disappeared from the region.


Waning rain fall in Udhagamandalam


The rainfall pattern was found to fluctuate with wooded land area in the hills. When the Nilgiri mountains had luxuriant forest cover annual rainfall used to be much higher.



Logging for valuable timber such as teak and mahogany not only involves a few large trees per hectare but about a dozen more trees since they are strongly interlocked with each other by vines etc.


Also road construction for making approach to the trees causes further damage to the forests.


In India, firewood demand would continue to rise in future mostly consumed in rural areas, where alternative sources of energy, are yet to reach.





Mining is the process of removing deposits of ores from substantially very well below the ground level.


Mining is carried out to remove several minerals including coal.


These mineral deposits invariably found in the forest region, and any operation of mining will naturally affect the forests.


Mining from shallow deposits is done by surface mining while that from deep deposits is done by sub-surface mining.


More than 80,000 ha of land of the country are presently under the stress of mining activities.

1 Effects of mining resources


Mining operation require removal of vegetation along with underlying soil mantle and overlying rock masses. This results in destruction of landscape in the area.


Large scale of deforestation has been reported in Mussorie and Dehradun valley due to mining of various areas.


Indiscriminate mining in Goa since 1961 has destroyed more than 50,000 ha of forest land. Mining of radioactive mineral in Kerala, Tamilnadu and Karnataka are posing similar threats of deforestation.




Big dams and river valley projects have multi-purpose uses and have been referred to as "Temples of modern India”.


India has more than 1550 large dams, the maximum being in the state of Maharashtra (more than 600) followed by Gujarat (more than 250) and Madhya Pradesh (130).


The highest one is Tehri dam, on river Bhagirathi in Uttaranchal and the largest in terms of capacity is Bhakra dam on river Sutlej.


Fig 3.6 Dams


1 Effects on Tribal people


The greatest social cost of big dam is the widespread displacement of local people.


It is estimated that the number of people affected directly or indirectly by all big irrigation projects in India over the past 50 years can be as high as 20 millions.


The Hirakud dam, one of the largest dams executed in fifties, has displaced more than 20,000 people residing in 250 villages.


2 Effects on forests


Thousands of hectares of forests have been cleared for executing river valley projects which breaks the natural ecological balance of the region. Floods, landslides become more prevalent in such areas.




The Narmada sagar project alone has submerged 3.5 lakh hectares of best forest comprising of rich teak and bamboo forests.


The Tehri dam submerged 1000 hectares of forest affecting about 430 species of plants according to the survey carried out by the botanical survey of India.

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