4.2. How is forest cover affected by human activities?
Some major direct and indirect threats to forests
can be identified but often multiple factors combine to cause greater
harm. In the case of tropical forests, deforestation has many complex
causes linked in particular to land use changes. More...
The most significant human-related, direct causes
affecting forest cover are listed below.
4.2.1. Conversion of forest land to agricultural
Humans have always cleared land for agriculture
either for subsistence or for larger scale settling and planting..
The FAO claims that former is less a threat to forests than the
latter. In developing countries, forestland is cleared under the
traditional system known as ‘swidden,’ or ‘slash
and burn’. Though blamed for deforestation, ‘swidden’
cultivation is actually quite sustainable, while clearance by migrants
usually has greater long-term impact. Agricultural development programs
initiated by governments, such as economic plans and resettlements
in Indonesia, can also have substantial impact on forests. In the
1980s, US fast food companies were blamed for some deforestation
in Central and South America caused by conversion to beef production.
This practice is less profitable today due to more stringent legislation.
4.2.2. Conversion due to infrastructure development
The conversion of forestland to infrastructure development
can take several forms, including road-building, hydroelectric dam
construction, and mining. Road construction reduces forest cover
both directly by occupying land, and indirectly, by fragmenting
the landscape and opening it up for exploitation. A study showed
that 86% of Amazonian forests lost between 1991 and 1996 were within
25 km of major roads. A similar process has occurred in Indonesia
and Central Africa. Dam construction is an infrastructure development
mostly affecting forests in Southeast and East Asia. Dams flood
large populated areas, forcing migration or resettlement to more
environmentally sensitive areas. This is turn leads to deforestation,
degradation of forests and increased erosion. Mining can also impact
forested areas usually immediately adjacent to the mine. Examples
include the discovery of minerals and especially gold in the Brazilian
Amazon and the mining carried out by large international corporations
in Irian Jaya (Indonesia). More...
4.2.3. Harvesting forests for timber
Harvesting is an important factor in the global
loss of forest cover but it often causes degradation rather than
deforestation, as old growth is replaced with younger ecosystems
or fewer species, or as areas are only partially logged. The extent
of forest cover is most threatened when farmers, ranchers and fuelwood
collectors move in to clear the land for other economic uses after
harvesting is complete. According to the FAO (FRA 2000), timber
harvesting takes place on some 110,000 km² of tropical forests
each year. More...
4.2.4. Harvesting forests for pulp and paper production
Paper manufacture accounts for some 14% of the total
world wood harvest. Most of the fibre used for pulp comes from managed
temperate forests (only 2% from natural hardwood or tropical forests).
The IIED in their study on “The Sustainable Paper Cycle”
found that the sources of wood fibre mainly originate from managed
natural regeneration forests (37%), plantations (29%) and thirdly
from unmanaged natural regeneration forests (17%). Original conifer
forest account for 15% while tropical rainforests and hardwood forests
account for only 2% of the global wood pulp. Europe, North America
and Japan are increasingly using recycled paper as a source of fibre.
Sometimes, inappropriate pricing of forest resources and credit
policies can lead to unsustainable investments in pulp and paper
mills. In Indonesia, for example, an overcapacity of paper mills
led companies to turn to natural forests after exhausting plantations.
4.2.5. Cutting of trees for fuel-wood and charcoal
Wood and charcoal are still the main source of energy
for most people in developing countries. Cutting trees for fuel
has visible impacts on forests, particularly near urban areas, but
most analysts now believe that this is not a major cause of deforestation.
While woodcutting for fuel does affect forest cover (especially
near urban areas), it is more of a social problem—in which
affordable supplies of fuel in urban areas are running out—than
a global deforestation problem. The wood energy research for the
last twenty-five years has reached the following consensual conclusions:
- Wood and charcoal are vital sources of energy in developing
- Urban use of wood fuel places the heaviest pressure on forest
- The main source for wood and charcoal are dry tropical woodlands.
- Programs to popularize ‘fuel efficient stoves’ have
had a very modest impact.
- Programs to promote the planting of fuel in woodlots, and improved
charcoal burning technologies may ease the scarcity of wood fuel.
4.2.6. Acid rain and atmospheric pollutants
The most common form of atmospheric pollution believed
to affect forests is ‘acid rain,’ defined as precipitation
containing high levels of sulfuric or nitric acid. Acid rain and
air pollution degrade forest vegetation. Damage varies with tree
species and soil composition. Research in Eastern Europe, where
in the past severe atmospheric pollution took place, is clarifying
the links between this pollution and forest vegetation. Forests
seem to recover well from mild pollution damage but more slowly
with severe damage. Research on forest recovery is under way in
an area of the Czech republic where 50% of the forest died in 1989
due to atmospheric pollution. On the other hand, there is evidence
that carbon dioxide in the atmosphere increases the growth rate
of forests. Radiation is another form of pollution. According to
the University of Voronezh in Russia, 70,000 km² of forest
in Russia, Belarus and Ukraine were degraded by the nuclear accident
in Chernobyl. More...
4.2.7. Loss of forests to fire
Human activities can start fires deliberately or
accidentally. These accidents can be caused by careless use of fire
for the clearing of land or other purposes. They can burn out of
control for long periods of time. Burned areas can recover but they
are vulnerable because fires open up large areas of forest and the
ash increases the fertility of the soil, thereby giving an incentive
to agricultural use. Areas of concern include the Mediterranean
forests, tropical forests and boreal forests in northern China and
A prominent example of deforestation by fire is the case in1997-1998
in Sumatra and Borneo (Indonesia). Although there was wide disagreement
at first, the final consensus is that 20,000 km² of land had
burned, only some of it being forest. Indigenous people and smallholder
farmers were accused of setting off the fires with their ‘slash
and burn’ techniques. In fact, dry conditions caused by El
Nino combined with a number of social, economic and policy factors
to create the disaster. More...
4.2.8. Destruction of forests in the course of
Warfare can lead to long-lasting deforestation.
Forest fires can be set off in a battle, deliberately or not. The
Vietnam War can be cited, but also conflicts in Myanmar (Burma)
and Sri Lanka. More...