90 Ecology and Applied Environmental Science
5.2.4 desert
Deserts may appear in areas with yearly rainfall less than 250 mm or in more
humid warm regions with an unequal yearly distribution of rainfall. Most are
found between latitudes 30° N and 30° S, although special local conditions
can create deserts elsewhere, too. In some extreme cases of deserts, draught
can last for many years. The water is usually the limiting factor in the desert;
that is why a desert’s productivity is more or less a linear function of rainfall.
Polar zones are types of deserts where the limiting factor is not the water but
temperature; Antarctica is considered as the largest desert in the word.
Plants and animals of the desert have developed many specializations for
water economy. Thus thick, waterproof trunks are observed in trees, as well
as a reduced surface or a special making of leaves (e.g. special trichome) that
helps the reflection of light. The plants may grow far apart but a shallow
root system develops in the ground so that absorption of rain can be maximized. Under special conditions of the soil, some plants develop deep roots
that reach the underground water table. Animals solve the problem of water
deficiency in many ways. Most of them become active at night, while during
the day they find shelter in places that offer coverage against high temperatures. Their excretory systems are suitable for water retention, and many
animals are able to use the water that is produced during cell metabolism.
5.2.5 the Forest as a natural resource
The forest is a complex and rich ecosystem as well as a valuable renewable
natural resource. Its direct offerings include:
• Forest biomass, as a fuel that is an energy source of decisive importance, especially for populations of some developing countries
• Timber and a series of other forest products that are still irreplaceable
raw materials
• The store of genetic material that can play the role of genetic reservoir for future improvements of agricultural production and of other
productive sectors
• The most significant, along with the oceans, shelters of the planet’s
wildlife
• The use of areas for recreation and enjoyment of nature, which is a
vital need of the inhabitants of cities in our times
The indirect offerings of forests are perhaps even more important for
man and include:
• Protection of drainage basins against erosion and the creation and
preservation of soil
5.2.4 desert
Deserts may appear in areas with yearly rainfall less than 250 mm or in more
humid warm regions with an unequal yearly distribution of rainfall. Most are
found between latitudes 30° N and 30° S, although special local conditions
can create deserts elsewhere, too. In some extreme cases of deserts, draught
can last for many years. The water is usually the limiting factor in the desert;
that is why a desert’s productivity is more or less a linear function of rainfall.
Polar zones are types of deserts where the limiting factor is not the water but
temperature; Antarctica is considered as the largest desert in the word.
Plants and animals of the desert have developed many specializations for
water economy. Thus thick, waterproof trunks are observed in trees, as well
as a reduced surface or a special making of leaves (e.g. special trichome) that
helps the reflection of light. The plants may grow far apart but a shallow
root system develops in the ground so that absorption of rain can be maximized. Under special conditions of the soil, some plants develop deep roots
that reach the underground water table. Animals solve the problem of water
deficiency in many ways. Most of them become active at night, while during
the day they find shelter in places that offer coverage against high temperatures. Their excretory systems are suitable for water retention, and many
animals are able to use the water that is produced during cell metabolism.
5.2.5 the Forest as a natural resource
The forest is a complex and rich ecosystem as well as a valuable renewable
natural resource. Its direct offerings include:
• Forest biomass, as a fuel that is an energy source of decisive importance, especially for populations of some developing countries
• Timber and a series of other forest products that are still irreplaceable
raw materials
• The store of genetic material that can play the role of genetic reservoir for future improvements of agricultural production and of other
productive sectors
• The most significant, along with the oceans, shelters of the planet’s
wildlife
• The use of areas for recreation and enjoyment of nature, which is a
vital need of the inhabitants of cities in our times
The indirect offerings of forests are perhaps even more important for
man and include:
• Protection of drainage basins against erosion and the creation and
preservation of soil