Deforestation is the conversion of forested areas to non-forest land for use such as arable land, pasture, urban use, logged area, or wasteland. Generally, the removal or destruction of significant areas of forest cover has resulted in a degraded environment with reduced biodiversity. In many countries, massive deforestation is ongoing and is shaping climate and geography.
Causes of deforestation
There are many causes, ranging from slow forest degradation to sudden and catastrophic
• clear cutting,
• slash-and-burn,
• urban development
• acid rain, and
• wildfires.
Deforestation can be the result of the deliberate removal of forest cover for agriculture or urban development, or it can be a consequence of grazing animals, primarily for agriculture. In addition to the direct effects brought about by forest removal, indirect effects caused by edge effects and habitat fragmentation can greatly magnify the effects of deforestation.
Impact On Environment
Generally, the removal or destruction of significant areas of forest cover has resulted in a degraded environment with :
•Reduced biodiversity.
•Changed climate and geography.
•Deforestation affects the amount of water in the soil and groundwater and the moisture in the atmosphere.
•Deforestation can destroy genetic variations (such as crop resistance) irretrievably
•Deforestation lessens the landscape's capacity to intercept, retain and transport precipitation. Deforestation also contributes to decreased vapor transpiration, which lessens atmospheric moisture which in some cases affects precipitation levels down wind from the deforested area .
Long-term gains can be obtained by managing forest lands sustainable to maintain both forest cover and provide a biodegradable renewable resource. Forests are also important stores of organic carbon, and forests can extract carbon dioxide and pollutants from the air, thus contributing to biosphere stability and probably relevant to the greenhouse effect. Forests are also valued for their aesthetic beauty and as a cultural resource and tourist attraction
Economic impact
•Historically utilization of forest products, including timber and fuel wood, have played a key role in human societies, comparable to the roles of water and cultivable land. Today, developed countries continue to utilize timber for building houses, and wood pulp for paper. In developing countries almost 3 billion people rely on wood for heating and cooking. The forest products industry is a large part of the economy in both developed and developing countries. Short-term economic gains made by conversion of forest to agriculture, or over-exploitation of wood products, often leads to loss of long-term income. Both West Africa and Southeast Asia have experienced lower revenue because of declining timber harvests. Illegal logging causes billions of dollars of losses to national economies annually
Forest Regeneration
Forest regeneration is the act of renewing tree cover by establishing young trees naturally or artificially-generally, promptly after the previous stand or forest has been removed. The method, species, and density are chosen to meet the goal of the landowner. Forest regeneration includes practices such as changes in tree plant density through human-assisted natural regeneration, enrichment planting, reduced grazing of forested savannas, and changes in tree provenances/genetics or tree species. "Human-assisted natural regeneration" means establishment of a forest age class from natural seeding or sprouting after harvesting through selection cutting, shelter (or seed-tree) harvest, soil preparation, or restricting the size of a clear-cut stand to secure natural regeneration from surrounding trees. "Enrichment planting" means increasing the planting density (i.e., the numbers of plants per hectare) in an already growing forest stand.
Definition and Purposes
Technically the term “dam” relates to the barrier constructed across a stream, valley or similar natural depression for the purpose of impounding water, but popular usage includes the impounded water along with the barrier.
Apart from the obvious requirements of storage for community or stock water supply, the economic purposes served by impounding of water by dams are: land irrigation, generation of electricity by hydraulic power, amelioration of flooding by partial retention of flood waters, and improvement of natural waterway facilities for inland navigation.
Hydroelectricity is electricity produced by hydropower. It is a renewable source of energy, produces no waste, and does not produce carbon dioxide (CO2) which contributes to greenhouse gases. Hydroelectricity now supplies about 715,000 MW or 19% of world electricity (16% in 2003), accounting for over 63% of the total electricity from renewable in 2005.
Negative Impacts of Hydroelectric Projects
•The construction of large dams completely change the relationship of water and land, destroying the existing ecosystem balance which, in many cases, has taken thousands of years to create. Currently there are around 40,000 large dams which obstruct the world's rivers, completing changing their circulation systems: this is not going to occur without dire environmental impactsThroughout the past few years, the negative impacts of dams have become so well known that most countries have stopped building them altogether and are now forced to invest their money into fixing the problems created by existing dams
Greenhouse gas emissions
The reservoirs of power plants in tropical regions may produce substantial amounts of methane carbon di oxide. This is due to plant material in flooded areas decaying in an anaerobic environment, and forming methane, a very potent greenhouse gases.
Soil Erosion
One of the first problems with dams is the erosion of land. Dams hold back the sediment load normally found in a river flow, depriving the downstream of this. In order to make up for the sediments, the downstream water erodes its channels and banks. This lowering of the riverbed threatens vegetation and river wildlife. One of the reasons dams are built is to prevent flooding. However, most ecosystems which experience flooding are adapted to this and many animal species depend on the floods for various lifecycle stages, such as reproduction and hatching. Annual floods also deposit nutrients and replenish wetlands.
Species Extinction
As fisheries become an increasingly important source of food supply, more attention is being paid to the harmful effects of dams on many fish and marine mammal populations. The vast majority of large dams do not include proper bypass systems for these animals, interfering with their lifecycles and sometimes even forcing species to extinction.
Changes to Earth's RotationNasa geophysicist have found evidence that large dams cause changes to the earth's rotation, because of the shift of water weight from oceans to reservoirs. Because of the number of dams which have been built, the Earth's daily rotation has apparently sped up by eight-millionths of a second since the 1950s. Chao said it is the first time human activity has been shown to have a measurable effect on the Earth's
Animal diseases
Animals are subject to a similar range of water related diseases as humans. They may also act as reservoirs for human water-based infections and infections with water-related insect vectors. The promotion of animal husbandry as a secondary, income generating activity for farmers in newly irrigated areas should be carefully evaluated for its possible environmental and health risks.
Aquatic weeds
The main problems of aquatic weeds are that they reduce the storage and conveyance capacity of reservoirs, canals and drains and increase water loss through evapotranspiration. Most irrigation schemes suffer infestations of exotic species. They are difficult and expensive to control, though the use of linings, shade and intermittent drying out can compliment traditional techniques of mechanical removal, careful herbicide application and the introduction of weed eating fish and insects.
Resettlement and Rehabilitation of people( its problems and concerns.)
•Towns and forests located in areas that will be inundated will have to be demolished and removed in order to increase navigability on the river. The loss of forests and agricultural lands will lead to erosion and the build up of sediment at the base of the river and reservoir. This could lead to increased flooding upstream. Sediments and silt contain valuable nutrients necessary to agricultural production. The blocking of sediments behind the dam means that these nutrients may not reach fertile farmland downstream of the dam. This could reduce the fertility of the land.
•The destruction of the villages also leads to problems of pollution. The Yangtze River is already polluted from the shipping of coal, acid rain, and its central location in Chinese industrial activity. Pollutants from towns and waste dumps that will be inundated will add to this pollution. Some funds were set up to aid in cleaning the area for the reservoir, but only the future will show whether a sufficient job was done. Water moves slower in the reservoir and some are concerned that the pollution will sit and worsen water quality of the river.
Population change
Irrigation projects tend to encourage population densities to increase either because they are part of a resettlement project or because the increased prosperity of the area attracts incomers. Major changes should be anticipated and provided for at the project planning stage through, for example, sufficient infrastructure provision. Impacts resulting from changes to the demographic/ethnic composition should also be considered. Training is an important component if new skills are expected.
Income and amenity
The most common socio-economic problems reducing the income generating capacity of irrigation schemes are:
• the social organization of irrigation operation and maintenance (O&M): who will carry out the work (both operation and maintenance); when will irrigation take place (rotation schedules); Poor O&M contributes significantly to long-term salinity and water-logging problems and needs to be adequately planned at the design stage.
• reduced farming flexibility. Irrigation may only be viable with high-value crops thus reducing activities such as grazing animals, operating woodlots etc.
• insufficient external supports such as markets, agro-chemical inputs, extension and credit facilities
Human migration
•Human migration (outside of the nomadic way of life) and displacement are commensurate with a breakdown in community infrastructure which results in a degree of social unrest and may contribute to malnutrition and an increased incidence of disease. Large, new irrigation schemes attract temporary populations both during construction and during peak periods of agricultural labour demands and provision for their accommodation needs to be anticipated. The problems of displacement during project construction or rehabilitation can usually be solved by providing short-term support.
Resettlement
•Often the most significant social issue arising is resettlement of people displaced by the flooding of land and homes or the construction of canals or other works. This can be particularly disruptive to communities and, in the past, insensitive project development has caused unnecessary problems by a lack of consultation at the planning stage and inadequate compensation of the affected population. Technical ministries should seek expert assistance at an early stage. Community re-establishment often includes, for example, pilot farms, extension services and credit schemes.
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