CAUSES OF THE DEFORESTATION IN THE WORLD

Forests are threatened by both biotic and a-biotic factors such as climatic hazards, diseases prompted by insects or pathogens, threats of a purely anthropogenic nature, fires, atmospheric pollution, deforastation, and the increase in social pressures.
But this classic division is a bit artificial, since man is partly responsible for all these threats. Indeed the mark of human actions is always present : it is however relatively moderate concerning climatic disorder despite the emissions of greenhouse gases, responsible for important destructions ; it is average in the sensitive growth of certain artificial forestry stands prone to parasitic attacks ; it is preponderant in the phenomena of atmospheic pollution or of deforestation. These aggressions will therefore be classed by groups but keeping an effort to maintain classification by growing order of mans implications, and therefore the possibility of theoretical intervention will also increase.

Climatic hazards and natural catastrophes

Climatic hazards or natural catastrophes are pratically independent from the actions of the man. However, the worries concerning eventual future climatic changes, due to the consequences of green house gases from industrial pollution are going to grow. It is sufficient to study here not the ways of fighting these aggressions, but those measures to take before forestry stands are subjected to these events.
Forests are submitted more than any other terrestrial ecosystem to climatic hazards, due to the duration of their maturity, wich can take up to 200 years. In such a period the number of climatic hazards can be great.

Storms and win-blow

Storms have had an important destructive effect throughout this century, especially throughout the last twenty five years in Europe, destroying millions of m3 of wood, the following examples being the most notable :
- 1972, in Northern Europe, 28 million m3 destroyed in 6 hours.
- 1982, 12 millions m3 flattened in France.
- 1987, 11.5 million m3 in the UK, Northern France and Belgium.
- 1990, almost 110 million m3 destroyed throughout Europe.
- 1999, 140 million m3 in France.
These anarchic destructions greatly perturb cutting cycles and general forestry work. Delaying The development of the forest and disrupting the wood market. Against such freak winds forestry management has very little power. However, although foresters are unable to prevent such catastrophes, they have the power to limit the destruction of violent winds by favouring the development of stands that are more wind resistant, and by adopting a prudent and diverse outlook towards management.

Periods of drought

Water stress renders forestry stands very fragile. They can arise either by a change in the distribution of water throughout the seasons, for the same quantity of annual precipitation (the supply therefore being brought forward in relation to the demand of forest stands), or by a fall in the annual volume of precipitation. It has now been established that the numerous cases of dieback observed in forests stands throughout the world in the last ten years (which at the time were entirely blamed on atmospheric pollution) are due in part, to periodic water stress. In fact, those observations realised concern those forests in regions subjected to strong pollution fall out, but also forests of less affected regions. Damage has been witnessed in Europe, Asia, North and Latin America, Sri Lanka and Hawaii. A certain number of observations take account of this point of view, a relative improvement, with a lowering in the intensity of dieback.

Biotic Threats

Diseases and the attack of insects : brief overview of the situation
Insects and fungi play an important part towards the causes of dieback in many forests of the world.
These biotic agents intervene, either as primary agressors, or most often as secondary agressors, often attacking already weakened stands. The examples of diseases and illnesses caused by pathogens are unfortunately numerous and only a few will be outlined. These illnesses develop, either as a result of native pathogenic activity, or by the invasion of the non-native agents in non-resistant stands. Robredo and Cadahia drew up a very complete table of the world situation concerning this problem during the tenth world forestry congress, from wich the following text is largely inspired (in COLLECTIF. - The forest, inheritance of the future - Acts of the tenth forestry congress . - French forestry revue. - Nancy, 1991.).

• In North Africa, natural cedar stands are attacked by xylophitic insects , during periods of climatic stress.
• In Spain, Abies pinsapo is subjected to combined attacks of theFungi Fomes annosus, and xylophitic and cortical perforating insects.
• In Europe, dieback can be observed amongst various oak species, most notably, the cork oak and evergreen oak (attacks of Diplodia and Hypoxilon).
• In Quebec, the pine shoot moth periodically attacks the annual shoots of (Abies balsamea and Picea glauca) as in the whole of the North East of North America. This indigenous insect reaches epidemic proportions roughly every thirty years. The last infestation (1938-1958) provoked the death of 60 % of Firs and 20 % of Spruces. At the end of 1975, an epidemic breakout covered 35 million ha of Quebec.
• In continental China, the beetle Hemiberlesia pitysophilla provoked the dieback of Pinus massoniana. In 1987, the area effected covered some 420.000 ha, but its extremly rapid progression soon put in danger more than 25 million ha, most notably in the province of Guangdong.

Those epidemics due to the introduction of new pathogenic agents are equally very frequent.

• Among wich Ceratocystis ulmi is responsible for Elm disease, having caused the death of the vast majority of this species throughout the 1980s in continental Europe.
• Bursaphelenchus xylophilus develops its attacks on the different species of pines in China, Japan, and Taiwan. It is in fact a nematode carried by an insect of the Monomacchusgenre. However, the most efficient mode of dispersion of this disease seems to be the commercial circulation of logs.
• Phoracantha semipunctata, originally restricted to Australia, has been recorded in the Republic of Central Africa at the beginning of the century, and has colonised practically all the eucalyptus stands, in North Africa, Spain, Bolivia and California.

Towards a preventive forestry management

Faced with these theats, the first measures to take must be of a protective nature and will concern the isolating of pathogenic agents by the putting in place efficient phytosanitary barriers. These phytosanitary protection measures require a good knowledge of the biology of pathogenic species, in order not to provoke the abusive disfunctioning of the international commerce of forestry products.
Silvicultural measures must be taken to improve the health of forests stands, and to stimulate their production and to avoid the causes of poor stand health, in order to prevent the action of secondary organisms. The maintenance of species diversity and stand types is equally important for an efficient fight against biotic threats.
The putting in place of forest protection methods requires a perfect knowledge of the biology of pathogenic agents, in addition to their hosts. The surface area generally threatened and the fragility of ecosystems concerned does not permit the use of methods of large scale intervention.
Biological control has developed greatly, notably with the utilisation of secondary parasites (such as Bacillus thurigensis), but still remains fairly limited. Chemical control is necessary in certain situations where the area is too vast, or in epidemic periods. Chemical control must be carried out with great care and selectively, as in the case in North America concerning the spruce Caterpillar.

Fires

Fire has always been an element present in many forestry ecosystems. Natural causes of fire exist such as lightening and volcanic eruptions. The area subjected to natural fires has been very important and can cover millions of hectares. However the lapse of time is generally long between successive fires, permitting the ecosystem to recover and reconstitute itself.
Large fires have always ravaged the surface of the earth. In the North of China, 1.33 million ha went up in flames in 1987 ; more than 3.5 million ha were burnt in Kalimantan (Borneo) between 1982 and 1983 ; in 1988, 400.000 ha were destroyed by fire in the United States in yellow stone national park. Recently in 1993, considerable damage was done by an enormous fire in Australia.

The importance of human factor

The main causes of contemporary fires and anthropogenic :

• This is the case with the recurrent fires in the European Mediterranean zone, or those fires provoked in tropical humid zones, which have their goal the clearing of land for agriculture.
• In dry tropical zones with mixed broadleaved forests and rich undergrowth, human populations have always used fire to make way for grazing and agriculture.
• In Europe, figures gathered by the FAO permit one to establish the area of forest burnt annually between 1980 and 1988, i.e. some 585.000 ha. During the same period North America lost some 3.5 million hectares of forest to fires. That percentage attribued to human causes being around 97% in Europe, 91% in the United States and 66% in Canada.

Very little is known concerning the equivalent information for the entire world. The total wooded surface touched by fire annually is around 10 million hectares, which represents some 0.3% of the total world forested area. However the impact of these fires is more important than this small percentage suggests. In fact, in the zones where the frequence of fires is high, the destructive character of such fires is worsened by the fact that forest stands do not have the time to reconstitute themselves between the passage of two consecutive fires.

An Integrated policy for the prevention and fighting of fires

The methods of fighting fires must be adapted to the socio-cultural environment in which they are put into place.

Developed countries

Developed countries possess the necessary materials to permit them to carry out a "No-fire" policy in order to satisfy public opinion, which is generally very sensitive to this form of threat to the natural environment. In this case, a perfect coordination between terrestrial and aerial fire fighting means must be provided, in addition to the active participation of the public and private forestry sectors, for example, in the participation of preventive operations and detective procedures.

Developing countries

In developing countries or in natural regions wich are less densely populated, one must accept that a part of the wooded surface will be burnt. This practice is due to an agro-silvo-pastoral culture wich includes positive elements and is therefore difficult to condemn. Solutions can not be looked for without taking into account the subsistence requirements of those populations concerned.

Deforestation and desertification

Generally speaking, deforestation is the result of an ambalance between natural resources and the need of the populations.
Before discussing this important subject, it is necessary to remember that developed countries (notably those of ancient civilisations such as Europe) have witnessed periods of very strong deforestation. Up until the end of the fourteenth century, the forests of Europe, which covered the majority of the region, have been the object of massive destruction. It is only recently that European forests have witnessed a phase of growth and improvement. Practically all the cultivated areas in Europe originate from more or less ancient deforestation. This is important when understanding the actual evolution of those countries in development and their relationship with their forested areas, and equally in avoiding certain judgements.
In fact, deforestation is only very rarely attributed to uncalled for malevolence. It responds to a necessity : either of economic development, or of survival. It can also be in certain regions, the extensions of urban zones and especially (harvesting of firewood) participates to this phenomena, but for less significant surfaces to the world scale.

Degradation of humid tropical forests - principle causes

Source: Coyte, (1990), cited by Gauthier (J.) in AFOCEL. - The emergence of new forestry potentials in the world - Colloque AFOCEL, tenth world forestry congress. - Grenoble, 1991.

The countries where the phenomena of deforestation is most evident are those undergoing rapid population growth. This population development implies two types of harmful needs to the durability of forests in the absence of specific developments.

• A growing need for wood, especially firewood for developing countries, then wood for construction
• A growing need for agricultural land, in able to assure the subsistence of populations.

The immediate satisfaction of these needs leads to the clearing and pillage of those resources that are closest to settlements. The fragility of these ecosystems does not permit them to withstand such pressure, and failure of the forest to re-establish itself can lead populations to carryout the same type of agression to forest areas that are further away, therefore participating in the extension of destroyed areas. Their reuse for agricultural purposes is oftten impossible (contrary to the old evolution of temperate zones) due to the extreme fragility of their soils.

The search for a harmonious coexistence

The indispensable association of populations
The restoration of a balance will only be possible if those responsible for development of these regions privilege small projects, using known techniques local populations and develop with them. In absence of the dangers of the dispersion of forests cover, and in the absence of a solution for the needs of agricultural development, no large-scale project can succeed, whatever the financial means put into place.
To maintain the soils of certain regions, forestry projects must be seen as factor of improvement in the long term necessary ecological conditions to agriculture and life in general, and not as a competitor for the use of the soil.

• In the dense tropical forest zones, shifting agriculture actually results in the clearing of forests by burning. But the need is such that the time for the forest to redevelop is too short. The drop in the impact of this burning can only take place by the growth (which seems paradoxical) of reserves where the clearing of ground is accepted, permitting the sufficient reconstruction of ecosystems.
• In zones such as the Sahel, the need for fuel wood is one of the most pressing concerns. The preservation of forests will only take place when combustion techniques are improved, the mass planting of fast growing tree species takes place and a more vigorous management of resources permiting the reconstitution of reserves is put into place.

Each different population has its own habits, specific needs, and determined environmental conditions which must be taken into account. Satisfying the needs of local populations is an indispensable perequisite to the putting in place of projects which take into account the needs of the populations, sometimes very far away from these zones.

The interdiction of timber exploitation : a badly adapted argument

The Interdictions of the commerce of logs of certain tropical species. Forestry exploitation has of course been at the root of numerous abuses in the tropical zone and participates in the degradation of forests from these regions. But these abuses are to be fought, it is not necessary to stop forestry exploitation of these zones. Here as elsewhere, the putting into place of a reasonable cutting regime could lead to sustainable growth of forests. In addition the impact of forestry damage due to the exploitation of logs when compared to the damage done by agriculture. Finally, the banning of this commerce will deprive those countries concerned of indispensable resources for the putting in place of necessary means for the resolution of the problems mentioned above, and it will prolong or aggravate the process.
The phenomena of desertification, and water erosion, are elsewhere very spectacular and concern a considerable part of our planet. Climatic fluctuations and destruction of the protective layer are the principle causes of this phenomena.