Our understanding about the quality and extent of forests of the world is very poor even today, Forest Wealth In most of the countries statistics on forests are either unreliable or absent altogether. Where some data exists it is plagued by definition problems.
How many trees and how close together they should be to be referred to as a forest? At what point does selective logging becomes deforestation? Does planting of one or few species, often on degraded land or once established cropland or on land cleared of standing forests mean reforestation? These are some of the basic aspects which have to be resolved properly before an exact assessment of global forests can be made.
However, some idea of the density and the extent of world’s forests can be had from the estimate of net primary production and total standing crop by Whittaker and Likens (1975). Though much uncertainty exists as far as area under each forest type is concerned, the data do provide a crude idea of global forest wealth. The existing forest of the world can be distinguished into the following three main types.
1. Boreal Coniferous forests. 2. Forests of the temperate belt.
3. Tropical rain and seasonal forests.
(1) Boreal Coniferous Forests:
Around the Arctic sea in the North, between latitudes 55° to 65° occurs a zone of coniferous forests which covers greater parts of Alaska, Canada, Scandinavia and Siberia with extensions further south at many places. Due to cold climatic conditions, the decomposition of organic matter is slow and forest floor tends to accumulate a thick layer of organic material which has an excellent water holding capacity. Decomposition of conifer needles renders the soil acidic. As far as nutrient status is concerned the soil is poor to very poor. The flora and fauna is characterised by low species diversity.
Coniferous forests are huge store house of soft wood to the mankind. These forests roughly stand over an area of about 1.2 billion hectares with a total standing biomass of about 240 billion metric tons on dry weight basis. Net primary production ranges between 0.4 – 2.0 kg per meters sq. per year with a total of about 9.6 billion metric tons per year on dry weight basis.
(2) The Forests of the Temperate Belt:
Temperature region extends from 30° to 55° latitudes on either side of the equator. This zone is characterised by marked seasonal changes in the pattern of temperature and precipitation which shape the vegetation. The forests of the temperate zone are spread over an area of about 1.2 billion hectares with a mean productivity of about 1.242 kg per sq. metre per year amounting to a total annual production of 14.9 billion metric tons on dry weight basis. The total standing biomass of these forests in terms of dry weight amounts to about 385 billion metric tons.
In regions which receive scanty rains, extensive grasslands and shrublands develop. Regions with a climate characterized by alternating dry and wet seasons give rise to deciduous forest in which the leaf fall is almost synchronous. Trees become leafless for periods between the fall and the appearance of new leaves. At places where sufficient moisture is available throughout the year forests of evergreen type develop. In these forests leaf-fall is almost continuous and the canopy is never naked.
Grass-land and shrub land constitute a very important natural resource for the mankind. It is these small plants – grasses, herbs, shrubs etc. – which support a large crop of wild and domestic animals such as horses, mule, ass, cows, buffaloes, sheep, goats, camel, deer, elephants, rabbit, zebra, antelopes etc. which in turn provide food, milk, wool, hide and transport to man.
Under the grasses and shrubs a thick layer of organic material accumulates on the soil, decomposition of which yields large amount of humus. This renders the soil exceedingly rich and fertile. Much of the grasslands and shrublands of temperate and sub-tropical zone of the world have, therefore, been brought under cultivation. Much of the rich, productive and intensively cultivated soils of the world lie in the temperate and subtropical belt.
(3) Tropical Rain and Seasonal Forests:
World’s densest forests are found in t-he warm and humid belt on either side of equator, between the latitude 30°N to 30.5°S, across Southern America, Central Africa, parts of India and East Asia. An outstanding feature of these forests is the richness and diversity of the biotic community. The vegetation is dense, stratified into many layers with tall trees usually covered with vines, creepers, lianas, epiphytes etc.
Under the tall trees there is a continuous ever-green canopy. The lowest layer consists of an understory of small trees, shrubs and herbs which become denser where there is a discontinuity in the overlying canopy. These forests are spread over an area of about 2.45 billion hectares with a mean annual production of about 2.017 kg per sq. metre per year amounting to a total annual production of 49.4 billion metric tons per year on dry weight basis. The overall standing biomass of these forests has been estimated to be 1025 billion metric tons which is about 55.5% or more of the entire weight of all living things on earth’s surface.
In tropical regions, warm climatic conditions promote rapid decomposition and mineralization of organic debris. The soil is subjected to heavy leaching while nutrient uptake by plants is also rapid. Cycling of mineral nutrients is, therefore, very quick.
At all times a large proportion of mineral nutrients occurs in biomass in a tropical forest whereas in a coniferous forest much of the nutrients I and organic matter lie on forest floor. A large portion of plant nutrients are removed when we clear a tropical forest for agriculture. The soil is made poorer and is unable to support cultivation for long durations.