Geoscience Reference
In-Depth Information
loss. The declining rate of woody biomass is the second highest in the world. It
ranges between 4 and 6 % per year. Almost 7,000-9,000 ha are deforested every
year and this rate is especially severe in the north where the per capita consumption
for fuelwood is ten times higher due to the ruthless winters.
Mangrove forests protect the port of Karachi against wave action and act
as nursery for shrimp. Mangroves are now under threat. Every major type of
forest or protective cover in Pakistan has suffered heavily in the recent past from
indiscriminate cutting, overgrazing, poor management and man-made ecological
changes. This has increased desertification, erosion and silting of reservoirs and
biological defenses against water logging and salinity are also deteriorated. The
ability to resist against soil erosion caused by monsoon rains is largely dependent
on vegetation and vigor of vegetation at ground level. Soil erosion increases on
degraded grazing land with sparse vegetation cover, which leads to siltation of
rivers and channels. Soil fertility declines due to removal of top soil resulting in
low production of forage, fodder, fuel wood, timber and grains. Soil erosion in the
watershed areas of rivers increases sedimentation load, which reduces the storage
capacity of dams.
Livestock Grazing Pressure:
Uncontrolled grazing of livestock is extremely
destructive to forest and vegetation cover. With the increase in livestock population
there is heavy pressure on natural vegetation. During period of feed scarcity,
thousands of cattle, sheep and goats depend on fodder plants, which are lopped to
the main stem. Unregulated livestock grazing reduces the productivity of rangelands
due to soil compaction, devegetation of fragile slopes, destruction of terraces and
selective destruction of growing trees and shrubs. As economy in desert regions is
pastoral, it affects both livelihoods of the desert dwellers as well as influences the
fragile environment.
Loss of Biodiversity:
Due to ever increasing human and livestock population there
is enormous pressure on natural vegetation in almost every agro-ecological region
of the country. Overgrazing of rangelands has extensively decreased the carrying
capacity. Some areas have also been affected by water logging and salinity damaging
the natural flora. Aridity and prolonged drought in arid lands have affected the
vegetation cover in these areas. All these factors have contributed towards the loss
of biodiversity in various regions of the country. As a result of degradation of natural
habitat as well as illegal hunting, 31 species of mammals, 20 species of birds and 5
species of reptiles are listed as endangered in the country.
Water logging and Salinity:
The major factor contributing to water logging in
cultivated areas is excessive percolation (leakage) from the canal system, which
builds up the ground water level.
The extent of waterlogged area is given in Table
12.9
. The figures are based on
the surveys which were completed in the late 1990s. It appears that problem of water
logging may not be as serious now as it was in the past. The problem has reduced
due to prolonged drought and excessive mining of ground water.
The human activities such as cultivation of high delta crops on highly or
moderately permeable soils, obstruction of natural drainage channels through
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