Roughly one third of the World's land area is forest land (4,126 million ha). Of this 3,712 million ha are actually covered with forest vegetation and this constitutes the world's forest area. These figures, and those shown in Table 1, are taken from the FAO World Forest Inventory 1963 and subsequent studies.
It will be seen that the developing regions account for 55 per cent of the total forest area. The Table also shows that close to 40 per cent of the total forest area is classified as unproductive and/or protective forests, and that this category is much more heavily represented in the developing than in the developed regions.
Table 1 - World Forest Area (million ha)
| Forest | of which unproductive and/or protective | |
| Developed Regions | ||
| North America | 710 | 300 |
| Europe (excluding USSR) | 148 | 22 |
| USSR | 738 | 38 |
| Japan | 24 | 1 |
| Oceania (developed) | 52 | 19 |
sub-total | 1,672 | 380 |
| Developing Regions | ||
| Latin America | 794 | 445 |
| Africa | 711 | 416 |
| Asia (excluding Japan) | 495 | 165 |
| Oceania (developing) | 40 | 25 |
sub-total | 2,040 | 1,051 |
Total world | 3,712 | 1,431 |
Governments have a special and in some ways unique position with regard to forests and associated lands. This is not only because of the direct economic utility of the forest domain in providing valuable raw material, spread over a relatively long production cycle: also and more often because it serves important public interests such as the preservation of scenic and recreational areas, and exerts a powerful and beneficial influence on man's environment, water supplies, agriculture and livestock farming.
These features have led many countries to retain large areas of forests and associated lands in public ownership and to have special laws and agencies for the management and development of such lands. Approximately 70 per cent of the World's forests is under public ownership.
Regardless of ownership vigorous governmental leadership is nearly always necessary to ensure and finance adequate measures for forest conservation and development. In many countries governmental responsibility is acknowledged over privately owned forests where public interests are involved. Such safeguards will no doubt in time spread to all countries.
In general terms, there is a fairly good correlation between the climatic conditions of a particular area and the types of forest vegetation occurring there. Higher altitudes at lower latitudes may produce forest types similar to those found at lower altitudes and high latitudes. The pattern is broken where special edaphic or hydrological conditions take prevalence in the determination of the vegetation type. Also the exposition - degree and direction of slope - is of much importance locally.
To the naturally occurring forest types must be added the so-called man-made forests which are of increasing importance, though their area is still modest in comparison with the total area of forest land 1. Attention should also be drawn to the tree vegetation, natural and artificial, outside the forests, of considerable relevance in many areas.
Appendix 1 gives a brief description of the major forest types of the world, while Appendix 2 contains information about the man-made forests.
All ecosystems function through primary producers, the green plants which synthesize simple inorganic substances into complex components, and secondary producers, the many organisms which utilise the primary material or its derivatives. Part of the secondary production is a decomposition, releasing nutrients for recycling. What characterizes the forest ecosystem are particular qualities with regard to such factors as structure, dimensions, complexity, maturity, stability, capacity for self-perpetuation and self-protection, and ability to influence and protect environmental parameters. The forest usually represents the ultimate stage in a vegetational succession. The forest community has developed as a result of a long evolution of species and populations of organisms and of the long process of their adaptation to the environment as well as mutually.
This characterization of the forest ecosystem is valid, evidently, within certain limits, and to a somewhat differing degree in different ecological zones. A constant feature is the inter-relationships and interdependence between the many components of the ecosystem. The destruction or the favouring of one component may have far-reaching effects which are difficult to forecast, or in any case require an intimate knowledge of the ecosystem for their evaluation.
The complexity of forest ecosystems varies with the climatic zones in which they occur. They are less complex where low temperatures or low humidity prevail, but retain the general characteristics. A summary account of the major problems connected with forest use, management and conservation in the temperate zones, the arid and semi-arid zones, and the tropical humid zones is given in the following section.
Man has been, and still is, a collector of forest products, a fisherman, a hunter, a keeper of domesticated animals, a shifting cultivator, a settled farmer, a constructor, a miner, and so on. The forests have been considered by man, at various times and conditions, as enemies, hunting grounds, protection and shelter, sources of several useful products, and sources of land for grazing and cultivation. Man's action, consciously or unconsciously, has as a rule been against the forest, rarely in its favour. Cutting, grazing and fires have over centuries caused a very marked reduction of the forest area in all continents. While such reduction is now essentially stopped in the developed countries, it continues in most developing countries, in many places at an alarming rate. Deterioration in quality and composition of the forest is common, but less conspicuous than reduction in area.
Today it is assumed that about half of the world's forests are subject to some form of control of their use or planning of their management. This ranges from very elaborate working plans to specifications in concession agreements (contractual) or in laws or regulations (legal). In some cases, control is not fully enforced and the rules remain partly theoretical. The figures in Table 2 show the situation in Europe where practically all forests are under some form of organized management, and in Africa and South America where this applies to only about 20 per cent of the forests.
Table 2
| (million ha)* | Working Plans | Legal and contractual | Others |
| Europe | 62 | 69 | 3 |
| Africa | 13 | 87 | 375 |
| South America | 10 | 105 | 445 |
| Pacific Area | 7 | 45 | 37 |
* Coverage for the four regions was 97, 61, 67 and 99 per cent, respectively.
The northern belt of the northern temperate zone is the southern, larger and more valuable part of the taiga, the cool coniferous forests. Then follow the mixed temperate forests which, together with continental steppes, constitute the major portion of the zone. Smaller areas of dry forests occur in the southern part (mediterranean countries, Texas, Arizona).
The southern temperate zone, with a much smaller land area (southern parts of Chile, Argentina and Australia; New Zealand), has warm temperate moist forests in New Zealand, Tasmania, parts of Victoria and N.S. Wales, and the SW-most tip of Australia. There are mixed temperate forests in Southern Chile, and dry forests and steppe elsewhere in the zone.
Forestry, optimum use of the forests with planning for sustained or improved yield, was born in the northern temperate zone, in Europe, and conversion from exploitation to planned use is more recent in North America and the USSR. 1
Major problems, apart from deficiencies in policy, legislation or planning in some areas, are 1) fires, 2) diseases and insects, 3) soil and water conservation, 4) mechanization and industrialization.
Fires change the environment, often drastically, over very large areas each year. Diseases and insects take a large toll of the forests, varying in intensity from year to year and from place to place. Forests on erodable soils and sloping ground must be managed for soil and water conservation as priority consideration. Mechanization, because of the heavy investment, leads to concentration of work with consequent negative effects, e.g. insolation, grasscover, soil compaction, damage to standing trees and to young growth, etc. Industrial plants cause pollution through their effluents, smoke etc. There is considerable damage to forests in the vicinity of industrial conglomerates.
Forest lands in the semi-arid zones are mostly open forests (forêts claires) or savanna woodlands; these formations occur in all parts of the world with severe dry seasons and are particularly extensive in tropical and sub-tropical regions. The overriding limiting factor is moisture, and the forest formations are frequently unstable and do not easily reconstitute themselves after destruction. Soils are erodable in many areas. Trees are usually short and badly formed, and growing stock volumes are in most cases low.
Dry forests have been extended over time by the action of man through grazing and forest destruction, typically in the Mediterranean region. In Africa there has been a century-long advance of the dry forests at the expense of the rainforests, due largely to fire, grazing, and shifting cultivation.
The dry forests are in many areas important producers of poles and fuel for the local population, and they constitute some of the world's most productive and best known wildlife habitats. They also furnish the areas for many of the world's new man-made forests, in the less arid parts.
In the less arid parts of the zone, priorities of use will have to be allocated and management adjusted accordingly. Problems are more acute in the more arid parts where the savanna woodland changes into various forms of therny scrubland, bordering the desert. To arrest the expansion of the desert (Sahara, Rajasthan, etc.) has been a much talked about subject in recent decades, and it is becoming still more important. One of the actions to pursue is to establish a stable vegetation cover in such sites of the desert fringes that will support the growth of selected, drought-resistant trees, shrubs and other plants.
The tropical rainforest, with its major occurrences in the Amazon basin, central Africa, and the south-east Asian coastal and island areas, is characterized by its large number of usually evergreen species and its multi-storied structure. On the fringes, a transition to sub-humid or moist deciduous types is the rule; in places the transition leads almost direct into dry formations.
Principles of sustained yield forest management were transferred from Europe and applied in some tropical forests, particularly in parts of South-East Asia. However, most tropical forests have remained either without any planned management or with various types of schemes or plans based on inadequate knowledge of the ecological (and social) factors at play. 1 Removal of the valuable species generally leads to quality deterioration, and this is accelerated by shifting cultivation and fires. The process may become irreversible, e.g. when soils are shallow or erodable.
The lines of attack are therefore the introduction of minimum management plans, attempts at settling the shifting cultivators, and some measure of fire control. The FAO Committee on Forest Development in the Tropics has in fact sponsored a code for the experimental management of tropical rainforests which is expected to be made available soon.
Relatively few tropical rainforests are constituted in such a way that it may be expected that they can be managed in perpetuity on the basis of natural regeneration in an economically and ecologically satisfactory manner. In most cases where the land is not ceded to agriculture or other uses, artificial regeneration is applied, ranging from sporadic enrichment planting to complete plantation establishment; in the latter case an entirely new ecosystem is developed, frequently consisting of even-aged stands of a single conifer species, with attendant risks from diseases, insects and fires.
Since continued expansion of forest plantations - man-made forests - is unavoidable, due to the increasing demand for industrial raw material, plans should now be made for the gradual reservation of very large and well distributed areas of tropical forest lands, to be managed for recreation, tourism, wildlife and products for local use.
As has been shown, forests occupy about one-third of the world's land area, and are to be found in almost all the regions of the earth. It is evident therefore that merely in terms of physical extent forests ought to exert considerable influence on the world's environmental quality. Moreover, forests are also the most complex of the ecosystems, and interact with other factors of the environment in an almost infinite variety of permutations. In consequence, the role of the forests in conserving and enhancing environmental quality is played not only at the local level, but also on a global scale.
It has been pointed out1 that the most important properties of the earth's surface which influence climate, and which are likely to be affected by human activity are reflectivity, heat capacity and conductivity, availability of water and dust, aerodynamic roughness, emissivity in the infra-red band, and heat released to the ground.
In all these aspects forests are important. The reflectivity of the forests is low because of the high light absorptive capacity of their green leaves when converting radiant energy to chemical energy. Indeed, it is well established that densely built up areas and deserts, and also grasslands, have a higher albedo2 than forests, and that a unit increase in the earth's albedo will cause a decrease in average surface temperature of 1.8°F. 3
Moreover, the capacity of the forests to absorb heat is high because large amounts of latent heat are fixed during the evapo-transpiration process. By contrast, forests have a low heat conductivity because their thick and complex structure prevents rapid cooling or heating, and regulates the heat released to the ground.
There is some conflict of opinion with regard to the influence of forests on the total water supply. However, there is little doubt that forests regulate water supply by restricting run-off during the peak rainy periods, and releasing water through springs and rivers during the dry seasons. Thus, the total amount of water available for use may be significantly increased through its release from the forests in those seasons when it is most needed.
Forests, by acting as windbreaks, also create aerodynamic roughness and assist in arresting dust particles. Their emissivity of the infra-red band is also very high. It is evident, therefore, that the forests play roles which affect all the important factors which influence climate.
Forests also affect the composition of the atmosphere. Green plants are the only organisms capable of converting radiant energy from the sun into chemical energy. During this process of photosynthesis carbon dioxide is assimilated and oxygen is released. The total rate of net photosynthesis is estimated to fix nearly 80 billion tons of carbon per year. When it is realized that nearly half of this process occurs in forests, their significance as atmosphere purifying agents would be clearly appreciated.
From time to time there have been predictions that the balance between carbon dioxide consumption and oxygen production would be disturbed. However, the effect of an increase of carbon dioxide in the atmosphere is the subject of considerable controversy in the scientific community. Be that as it may, it seems certain that the biosphere would respond to an increase in atmosphere carbon dioxide by increasing photosynthesis. As carbon dioxide consumption is to a great extent linked to the forest ecosystem, the presence of forests tends to counteract such a trend.
Forests, therefore, are one of the climatic buffers on which mankind depends - a buffer which, because of its complex organic structure, is able to withstand somewhat severe perturbations of its physical environment, provided that the changes and stresses to which it is subjected are not pushed beyond a certain threshold.4
1 Wilson, C.L. (Ed.) (1970) - Man's Impact on the Global Environment. M.I.T.
3 USA Congress (1970) The first Annual Report of the Council on Environmental Quality
4 E.P. Odum - The Strategy of Ecosystem Development. Science Vol.164 (April 1969)
The influence of forests on the human environment at the local level may perhaps best be classified as (i) physiochemical; (ii) mechanical; and (iii) psychophysiological. 1
The physionomy of the forests is such that it provides an extremely efficient barrier to precipitation. When rain 2 falls its downward progress to the forest floor is impeded by the canopy of the forest, and by the various layers of vegetation within the forest.
The interception storage capacity (the maximum amount of water that can be retained by the canopy) varies from stand to stand and from species to species, and is also influenced by the frequency and intensity of rainfall. 3 Its values, which are usually expressed in terms of equivalent rainfall over the area occupied by the stand, may range from 0.3 to 7.6 mm for conifer stands, and from 0.2 to 2.0 mm for deciduous forests. 4
Intense rainfall releases energy with a tremendous dispersion capability. Thus, it has been calculated that 50 mm of rain per hour would have six million foot pounds of kinetic energy - sufficient to raise a 17 cm layer of soil to a height of one metre over the same area. 5 The forest canopy by intercepting rainfall causes changes in the rate and time of water delivered to the ground, and, most important of all, dissipates the energy impact of rainfall.
Forests offer another line of defence. The accumulated litter on the forest floor acts as a cushion which absorbs the impact of the falling water, and prevents drainage to the soil beneath. This cushioning litter layer also takes account of any unintercepted rain which may fall directly onto the forest floor through the open spaces of the forest canopy.
The result of this interceptive power of those parts of the forest that are above ground is that there is little or no compaction of the forest soil. This is an important service in the protection of the soil against erosion, and in the regulation of water yield. If the soil is bare and unprotected, the impact of the rain leads to its compaction, clogs its pore spaces, and reduces its infiltration capacity. The water does not therefore penetrate into the soil but runs off, taking with it the soil particles. Apart from its impact-absorbing effect, the litter layer, because it is not a smooth surface, reduces run-off by providing obstacles to the unintercepted overland flow.
In addition to vertical interception, there is also what is sometimes called horizontal interception. The edge effects that are provided by forests on the horizontal movement of water may be of local hydrological significance. Perhaps the best known type of horizontal interception is that which occurs when fog clings to vertical surfaces and gives a fog drip or occult precipitation when an ordinary rain gauge in the open records nothing. For example, in the Canary Islands, during a period of a year, condensation of mist in a Eucalyptus forest trebled the rainfall, whilst on the south-eastern banks of Hokkaido in Japan, the equivalent of 3 mm of rainfall were obtained in 27 hours from fog drip in deciduous stands. In Panama “cloud forest associations cover sites where the presence or absence of forest cover definitely makes significant difference in total runoff and rainfall. The taller the vegetation cover, the greater the condensation of water on foliage and branches. Without some regulatory mechanisms the trees would grow so tall, condense and drip to the ground so much water that the soil would become too swampy for good growth of the large trees which would fall down due to unstable soil conditions combined with shallow rooting, ...... epiphytic vegetation becomes sufficiently abundant to utilize through transpiration and to catch the drip from above which prevents tree growth in height. Since cloud-cover and condensation on high ridges are frequent phenomena during the dry season, the water from condensation is extremely important for power development and irrigation projects.”1
Forests do not only reduce the impact of the rain on the soil; they actively assist infiltration, i.e. the movement or flow of water downwards through the soil surface. This is very useful, for if run-off is reduced or retarded, the only alternative to infiltration is undesirable permanent water-logging.
The organic matter which falls to the floor of a forest (leaves, twigs, flowers, fruits, branches, etc.) is first oxydised and hydrolised. Later, fungi decompose the solid matter still further and the soil fauna transports the resulting material downwards into deeper layers. The combined effect of this chemical and biological action is the conversion of the litter into humus. The presence of humus in the soil at the immediate soil surface improves its texture, increases its permeability, and therefore aids infiltration.
But this is not the only result of the presence of organic matter on the forest floor. The plant residues, in addition to providing food, also furnish favourable living conditions for various micro-organisms. Some of these micro-organisms penetrate the upper layers of the soil, and thus, in addition to transporting organic matter, they create a capillary system which permits the easier infiltration of water. As the roots of trees decompose, they also leave channels which serve as downward passage ways for the water retarded on the soil surface by the litter layer.
It is apparent, therefore, that the forests decrease surface run-off, increase the infiltration capacity of the soil, and assist the percolation of water downward through the soil. This is an extremely important service to the community, for if most or all of the rain which falls is permitted to run-off the surface of the land, the consequences may be very far-reaching. First, the existing drainage system may be unable to accommodate all the water released during the rainy season and this may lead to severe flooding, and the occurrence of torrents. Secondly, as water moves more rapidly over the surface of the land than through the soil, its ability to remove soil material is increased when there is no vegetation cover, and erosion is accelerated. The soil materials that are removed by the water are eventually deposited, and may cause great damage by filling and silting reservoirs, raising river and stream beds, and covering farmlands. Thirdly, by reducing the over-land flow during the rainy season and releasing it more slowly, to the springs which feed the streams, in the dry season when it is most needed, the forests help to regulate the supply of water and reduce the possibility of droughts. Fourthly, in addition to its cushioning effect, and the part which it plays in increasing infiltration, the litter layer on the forest floor acts as a filter which purifies the water which eventually reaches the streams. Also, by reducing the overland flow with its high concentration of sediment, the forests in yet another way contribute to the relative purity of the water. Indeed, the influence of forests on various elements of water quality such as temperature, colour, taste, microbial population, suspended sediments, and dissolved solids is very frequently positive under undisturbed forest conditions.
The importance of the physiochemical functions of forests may be illustrated by the following examples. It has been found that under certain conditions, only two percent of a 50 mm per hour rainfall ran off the surface of the land when there was 70 percent forest cover. However, in similar conditions but with forest cover reduced to 37 percent and 10 percent, the surface run-off increased to 14 and 73 percent respectively. Moreover, the amount of soil eroded varied with the degree of forest cover. Thus only 0.05 tons per acre eroded from the area with 70 percent forest cover while 0.5 tons per acre and 5.55 tons per acre were respectively eroded from the areas with 37 percent and 10 percent forest cover. 1
Over a period of twenty-one years the sediment yields from areas under forests have been compared with those from other types of land-use. It has been found in the areas investigated that under forest conditions sediment yield was about 50 tons per acre per year, from urban and suburban land 50 to 100 tons, from farmland 1,000 to 5,000 tons, and from land stripped for construction 25,000 to 50,000 tons with an average annual run-off of 15 inches; the maximum turbidities in parts per million were 45; 90; 4,500 and 45,000 respectively in the various areas described above. 2
This type of result has been used by foresters in providing communities with required amounts of water, in regulating its quality, and in controlling the period of its release. For example, if the major aim of watershed management is to increase water yield, then the density of the forests should be reduced to a safety limit which while decreasing interception and evapo-transpiration would ensure that sufficient cover is provided to minimize erosion.
1 FAO (1962) Forest Influences.
Winds can exert a quite deleterious effect on plant and animal growth and productivity. This is caused by their dessicating effect, by their impact on temperature, humidity, and snow cover, by their abrasive action, and by the soil erosion which often occurs when wind velocities are high.
One way of overcoming the necessarily attendant problems is to modify the micro-climatic conditions by erecting windbreaks or shelter belts of forest trees. As a consequence of the more favourable environment created by these trees, crop and animal yields are often increased. Moreover, as shelterbelts are usually established in treeless regions, they also improve the amenity value of the areas in which they have been laid down, and provide recreation and facilities that might otherwise not be available.
Shelterbelts and windbreaks reduce wind velocities. When wind strikes the shelterbelt, part of the air current passes through the belt and then divides into minor turbulances; another part rolls over the belt; the remainder rises above it. The effect of a shelterbelt on wind velocity depends on the height and permeability of the belt, the lay-out of the belt in relation to the prevailing wind, and on whether the shelterbelts are laid down as a system.
Although the extent of the protected zone is proportional to the height of the windbreaks, and is determined almost entirely by this factor, the density or permeability of the shelterbelt is of considerable importance in reducing wind velocity. Dense shelterbelts, although providing a greater degree of shelter immediately leeward, do not give the same degree of protection even at shorter distances away from the barrier. On the other hand, permeable barriers provide adequate protection at far greater distances.
It appears that the optimum permeability is between 30 and 55 per cent, and the effect of permeable belts on wind velocity increases considerably with growing speed. For example, if wind velocity goes up from 3.3 to 7.5 m/sec, the capacity of a five-row belt to reduce wind speed increases by 11 per cent.1
The direction of the prevailing wind is also important. The greatest reduction of wind velocity is obtained when the shelterbelt is at right angles to the prevailing wind. As the angle of incidence to the wind increases, the belt's effectiveness decreases.
Shelterbelts and windbreaks are more capable of reducing wind velocity when they are laid out as a system than if they consist of unrelated individual belts. A system of shelterbelts may have an accumulatively reducing effect on wind speeds; such systems increase the roughness of the ground surface, thus providing more resistance than bare areas.
The services which shelterbelts provide are quite remarkable. Their influence on air temperature varies at different times of the day and with different seasons as well as with the structure of the belt. The reduction of the vertical diffusion and mixing of the air usually results in an increase of temperature by day and a decrease by night.
Both the absolute and relative humidity near the ground are usually higher than in the open. The moisture content of the air in sheltered regions is therefore significantly greater than in areas of unobstructed wind and total evapo-transpiration is reduced. Studies carried out in Uzbekistan by the Central Asian Forest Research Institute have established that on sheltered irrigated land, humidity was 10 to 15 per cent higher in the month of July than on open land. In dry farming areas, relative humidity was found to be 5 to 12 per cent higher on the leeward side of a semi-permeable shelterbelt, and 6 to 18 per cent higher on the same side of a permeable shelterbelt than in open areas.
Most studies have indicated that evaporation is considerably decreased on the leeward sides of shelterbelts, because of reduced wind movement and increased atmospheric humidity. Moreover, soil moisture is higher in protected areas than in open fields. In the USSR, the moisture content of the top metre of soil has been found to be 25 to 30 per cent higher in the middle of protected fields.
However, because of root competition, soil moisture is generally low in those sheltered areas immediately adjacent to the windbreak.
On the basis of extensive research carried out in many parts of the world, the influence of shelterbelts and windbreaks on soil properties may be summarized as follows. Shelterbelts
protect the soil (especially fine-textured and sandy soils) against wind-blow;
create water stable aggregates and improve the soil's porosity, infiltration capacity and resistance to erosion;
increase the soil's water-holding capacity;
result in a higher humus content, more nitrogen and phosphorous, deeper carbon accumulation, fewer sulphates, and less water soluble salts;
increase the depth of the A horizon; and
activate micro-organisms thus increasing the effectiveness of certain fertilizers.
Because of their ameliorating effects on the micro-climate and on the soil, and because of the physical protection which they provide, shelterbelts increase the quality and quantity of the crops which they shelter.
The positive effects of shelterbelts are, of course, most noticeable in areas where growing conditions tend to be critical. Thus, in an area in which precipitation was the limiting factor, yields of summer and winter wheat, rye, oats, and alfalfa were between 150 and 300 percent higher in areas protected by shelter-belts than in unprotected fields. Moreover, the rate of germination, flowering, and boll formation and production of cotton was considerably increased by the provision of shelterbelts. In addition, cotton plants grew higher, produced heavier cotton bolls, and gave higher cotton yields, Where shelterbelts have been used to protect fruit and vegetables, physical damage has been reduced, yields have been increased, and ripening has been earlier. Shelterbelts and windbreaks also offer protection to livestock from excessive winds and heat. The belts have been shown to improve the respiration of cattle, to reduce their body temperature, to decrease calf mortality, and to improve beef and milk yields. Flocks of ewes raised under shelterbelts have been observed to produce 20 percent more wool per head, to be 30 percent heavier at the time of slaughter, and produce 30 percent more lambs. 1
Because of the diverse nature of the physiography and floristic composition of forests, because of the variety of fauna which they shelter and for which they provide food, because of the streams, rivers and lakes that are generally to be found in them, and because some regard them as things of beauty, forests have come to provide what may be described by the generic term of recreational services.
From time immemorial, the nobility had used the forests for relaxation and sport. Indeed, the earliest forest laws were primarily concerned with hunting and fishing, and although the Forest Code which Charles V of France promulgated in the XIVth century was designed to provide timber for a navy, the recreational aspects of forestry were not neglected. Manwood's treatise on the forest laws of England, which he published in 1717, was also chiefly on hunting and the protection of animals for sport.
During the last two decades or so, the use of forests for recreation has grown considerably, particularly in the developed countries. There are several reasons for this increase in recreational demand. First, there is a general reduction in the number of working hours of the average person and a consequent increase in leisure time. Second, standards of living are rising. Third, societies all over the world are tending to become more urban, and for some psychological reason, people tend to seek relaxation in areas that are dissimilar. Fourth, with the growth of industrialization, there appears to be a need to escape from the often soul destroying effects of an industrial society.
Many people go to the forests for recreation, not merely because of their aesthetic attractiveness, but perhaps because of the instinctive belief that they would “do them good”. This instinctive reaction is supported by the available evidence. Forests, because of their structure and functioning, increase the salubrity of the air by fixing dust and other impurities on the surface of leaves, and by the assimilation of ozone. Forests also create changes in the turbulent pattern of the wind, thus reducing the air's propensity to pick up impurities.
Forests may also make a valuable contribution toward alleviating the physical and mental stress which often results from over-crowding in urban environments. In this respect, the observed facility of forests to absorb noise may be of considerable importance. Preliminary studies indicate that appropriate barriers of trees and shrubs can reduce the sound level by as much as 10 decibels. This is approximately a 50 per cent reduction in apparent loudness.
People also go to the forests to observe wildlife in its natural habitat. Forest areas have always been a vital habitat for wildlife as they provide the essential features of life: cover, food, and water. The diversity of forests permit a corresponding diversity of wildlife. Indeed, without forests many species of animals, such as Brown Bear in Europe, gorillas in Africa and Cebid monkeys in South America, could not survive.
Careful attention must be paid to the wildlife aspect in developing forest resources. In many areas, multipurpose use is the best approach to rational management.
The contribution which the forests make to the human environment has been emphasized in the previous pages. However, the forests are not inviolate, and in many parts of the world they are being razed to the ground. They are being felled to yield new areas to produce food for rapidly increasing populations, to provide the wood raw material for forest industries, to earn foreign exchange in the booming world trade for forest products, and to absorb labour from the growing ranks of the unemployed. The possible impact of forestry and forest industries development is reviewed in the following sections:
It is not the intention of this paper to advocate the world's forests be preserved and left untouched. If forests are to contribute to the growth of national economies, and, at the same time, preserve and enhance the quality of the human environment, they should be managed scientifically. Scientific management implies interference - but a rational, informed and knowledgeable interference; not the uncontrolled exploitation of large areas of the forest ecosystem.
In Latin America, between five and ten million hectares of forests are felled annually for agriculture. In the Far East as a whole, it is thought that there are about 24.5 million shifting cultivators who annually fell forests up to approximately 8.5 million hectares, and that the total area under shifting cultivation is at least 103 million hectares. 1 2 The opinion has been expressed that in Africa, south of the Sahara, the area of closed tropical high forest has shrunk by at least 100 million hectares from its original extent because of this system. 3 For example, in the Ivory coast, forest inventories were made in 1956 and 1966. In the intervening period, 2,800,000 hectares, or 30 per cent of the area covered by forests in 1956, were cleared by itinerant cultivators. 4
FAO has estimated that in Burma timber of the value of $31.5 million is destroyed by shifting cultivation each year. In Guinea the figure is $40 million; and in Colombia it rises to $80 million. 5
The main reason for the rapid spread of shifting cultivation is, of course, the high rates of population growth which are occurring in tropical areas. However, as has been pointed out, 6 the land under shifting cultivation is capable of supporting only a population of less than twenty persons per square mile, and in general the system is fairly stable at that level. Where, however, the population increases, the fallow period is necessarily shortened, soil deterioration occurs, and productivity is reduced.
Therefore, there is very little that is intrinsically wrong with the system of shifting cultivation under conditions of low population densities, and relatively extensive land areas. There are even some examples which show that conservation and production can be reconciled. 7 As practised today, however, it not only reduces the economic potential of the nation's forests, but it also adversely affects the environment.
In some cases forest exploitation also contributes to the reduction of the services which forests provide. Because of the special characteristics of wood as a raw material, the high linkage effects which are engendered in the various types of wood processing and the importance of wood and wood products in international trade, forests and forest industries have come to be regarded as being of special importance in the attack on economic under-development. 8 Not surprisingly, therefore, Governments have in many cases granted concessions to exploit their forests.
Unfortunately, in many cases the chief concern seems to be rapid exploitation. As has been shown, among the reasons for the faculty of forests to regulate and purify water supplies and to reduce erosion are the presence of a litter layer which reduces surface soil compaction, and the high humic content of the surface soil which increases its infiltration and filtering capacities. Unfortunately, the efficient transportation of forest products often entails the building of roads and the use of quite heavy equipment. This almost inevitably leads to the disturbance of those conditions which make forests such a remarkable reservoir and purifier. As has been said, the “beneficent effects derived from long-time protection can disappear rapidly under the tractor … or trampling of a short-term harvesting operation”. 1
As far as the deleterious effects of logging on forest soils is concerned, it has been pointed out, for example, that, although crawler tractors, compared with wheeled vehicles or horses, exert the least compaction 2, their over-all effect may be more adverse because of the greater area of soil subject to mechanical vibration.3
Moreover, as the very existence of forest cover minimises erosion, it follows that in areas susceptible to erosion, where there is intensive logging with its clearances, extraction roads, storage depots (and with the attendant compaction of the soil) there is danger of increased erosion.
Similar problems may arise when production forestry is practised in forests which are in demand for recreation. In general, recreationists do not like to see unsightly clearings, accumulated forest waste, tree stumps, and all the mechanical paraphernalia of extraction. Forest production may therefore, unless carefully conceived and executed, have a limiting effect on the use of forests as centres of recreation.
On the other hand, visitors to the forests can seriously hinder forestry activities. They can trample on the soil and compact it, tread on and uproot seedling regeneration, light fires and burn forests to the ground, and cause damage to the growing trees, making them susceptible to subsequent insect and fungal attack.
There is no intention to labour these points. Foresters have over the years evolved systems of management and methods of exploitation which safeguard the forests against damage, provide the wood raw material for the development of industries, and at the same time ensure that the effects of exploitation on the human environment are positive rather than negative. Sound forest management planning includes conservation of the resource; this does not mean withdrawing it from human interference. These aspects of forest management are discussed in Chapter II.
1 FAO (1961). Timber Trends and Prospects in the Asia-Pacific Region, FAO, Rome
3 FAO (1966). Wood - World Trends and Prospects. Unasylva, Vol. 20 (1–2)
7 FAO (1957) - Hanunoo Agriculture in the Philippines
1 Lull, H.W. (1959) - Soil compaction on forest and range lands. USDA Misc. pub. No. 768
3 Huberty, M.R. (1944) - Compaction in Cultivated Soils. Trans. Amer. Geog. Union 25
Forest industries, particularly the pulp and paper industry, are considered to be substantial polluters of air and water. It is quite true that if these industries are operated strictly from the point of view of obtaining maximum financial returns there would be very substantial pollution. Indeed there have been many cases when this situation has prevailed.
As time is going by, however, the necessity to pay increasing attention to the impact of industrial production on the environment is forcing many of these industries to reduce or eliminate pollution. It should be emphasized that the control or elimination of pollution is not a technical problem; it is purely an economic question. The expenditure involved to control pollution is substantial and in some cases the industry cannot afford to do it or, as stricter pollution limits are established the producer's financial burden may eventually become so great that he is forced to increase the selling price of products. The necessary increase in capital costs in a typical big pulp and paper mill could be as much as 5–10 per cent in addition to a noticeable increase in manufacturing costs.
Pollution is also created by the mechanical woodworking industries such as sawmilling, plywood, particle-board and fibreboard manufacture. Wood waste, such as sawdust, offcuts, etc., is or used to be disposed of by burning, when it has no other use or value. It is obvious that such incineration creates such pollution as smoke and ashes.
The pollution control problems faced by the pulp and paper industry are, of course, much more complicated than those associated with the mechanical woodworking industries. Many pulping processes result in the production of unpleasant gases and odours. Pulping processes remove from the wood up to half of its weight by dissolving the compounds which bind the fibres together. While it is normally an economic necessity to recover the dissolved wood compounds and the chemicals used to process the wood, it is difficult to justify economically a 100 per cent recovery. Pulping of wood also normally produces very small fractions of fibre of low value, the recovery of which is very expensive. It should be noted, however, that pollution created by the pulp and paper industry does not always have the same effect on the population as pollution from many other industries, because the pulp and paper mills are normally located away from urban areas.
