Values, Alterations and Degradation of the Natural Landscape 95
erosion. China’s examples are characteristic, where the large population and extensive exploitation caused degradation and disaster due to
erosion of one-third of the country’s surface centuries ago. The cases of
Mediterranean countries are similar. The mountain areas have lost the
largest part of their soil in the course of centuries. The causes are the same
everywhere: thoughtless tree felling, fires, and above all, over-grazing. The
rates of the degradation differ, though, and are related, inter alia, with
historical factors such as wars, invasions of various raiders, the actions of
pirates, the presence of organized states that protected the public works
and were setting limits to over-exploitation etc.
The extreme pressure of grazing operates mainly in mountain areas with
steep inclines. The number of animals per surface unit plays a decisive role,
because when it exceeds certain limits, vulnerable natural vegetation does
not have the time to recover from the excessive exploitation and becomes
degraded. The kind and composition of phytocoenoses change, and gradually the ground becomes bare, which reduces its resistance to erosion. The
footsteps of the animals that continuously tread the ground cause serious
erosion along the routes they follow. Starting from those sensitive zones, the
erosion process continues unrestrained towards the neighbouring points.
The most catastrophic combination is the one of grazing following a
fire. The natural regeneration of vegetation is greatly sought after by
herbi vorous animals and gets destroyed; as a result, the system’s ability
to recover is counteracted after the fire. In this case, not only over-grazing
but even limited grazing can have catastrophic consequences. The results
are the same in the case of two consecutive fires in a period of a few years.
Erosion can act even in lowland areas with small inclines. This horizontal erosion carries away the fine soil particles and amasses them at the
lowest point reducing the land’s fertility. Ploughing along vertical contours,
the large extent of the fields and the abolition of plant hedges create favourable preconditions for the erosion of even almost horizontal surfaces.
Wind erosion is also significant in open areas, like the steppes. It is caused
both by over-grazing and the cultivation of marginal grounds and it is profoundly manifested after long periods of draught. The kind of cultivation
also plays a significant role, because friable earth needs proper vegetative
cover in order to resist the wind or the surface water flow.
The damage caused by the erosion of cultivable lands of the planet is huge.
The phenomenon has been studied especially in the United States, where in
1950 it was realized that two-thirds of the cultivable land showed signs of
erosion. It is estimated that in the duration of a century, an expanse of land
that equals one-fourth of the lands that can be cultivated was degraded by
erosion in the whole planet. Therefore the preservation of the productive
potential of the ground that is already under cultivation should constitute a
basic priority of agricultural policy on a global scale.
erosion. China’s examples are characteristic, where the large population and extensive exploitation caused degradation and disaster due to
erosion of one-third of the country’s surface centuries ago. The cases of
Mediterranean countries are similar. The mountain areas have lost the
largest part of their soil in the course of centuries. The causes are the same
everywhere: thoughtless tree felling, fires, and above all, over-grazing. The
rates of the degradation differ, though, and are related, inter alia, with
historical factors such as wars, invasions of various raiders, the actions of
pirates, the presence of organized states that protected the public works
and were setting limits to over-exploitation etc.
The extreme pressure of grazing operates mainly in mountain areas with
steep inclines. The number of animals per surface unit plays a decisive role,
because when it exceeds certain limits, vulnerable natural vegetation does
not have the time to recover from the excessive exploitation and becomes
degraded. The kind and composition of phytocoenoses change, and gradually the ground becomes bare, which reduces its resistance to erosion. The
footsteps of the animals that continuously tread the ground cause serious
erosion along the routes they follow. Starting from those sensitive zones, the
erosion process continues unrestrained towards the neighbouring points.
The most catastrophic combination is the one of grazing following a
fire. The natural regeneration of vegetation is greatly sought after by
herbi vorous animals and gets destroyed; as a result, the system’s ability
to recover is counteracted after the fire. In this case, not only over-grazing
but even limited grazing can have catastrophic consequences. The results
are the same in the case of two consecutive fires in a period of a few years.
Erosion can act even in lowland areas with small inclines. This horizontal erosion carries away the fine soil particles and amasses them at the
lowest point reducing the land’s fertility. Ploughing along vertical contours,
the large extent of the fields and the abolition of plant hedges create favourable preconditions for the erosion of even almost horizontal surfaces.
Wind erosion is also significant in open areas, like the steppes. It is caused
both by over-grazing and the cultivation of marginal grounds and it is profoundly manifested after long periods of draught. The kind of cultivation
also plays a significant role, because friable earth needs proper vegetative
cover in order to resist the wind or the surface water flow.
The damage caused by the erosion of cultivable lands of the planet is huge.
The phenomenon has been studied especially in the United States, where in
1950 it was realized that two-thirds of the cultivable land showed signs of
erosion. It is estimated that in the duration of a century, an expanse of land
that equals one-fourth of the lands that can be cultivated was degraded by
erosion in the whole planet. Therefore the preservation of the productive
potential of the ground that is already under cultivation should constitute a
basic priority of agricultural policy on a global scale.