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SUMMARY OF POTENTIAL IMPACTS OF FORESTRY ACTIVITIES WITH EMPHASIS ON THE TROPICS AND SUBTROPICS: BY ENVIRONMENTAL ASPECT OR SOCIO-ECONOMIC CONCERN
ENVIRONMENTAL ASPECTS OR SOCIO-ECONOMIC CONCERN
May become unstable, prone to slipping, sliding or earthflows; may become more
vulnerable to earth quakes.
Banks and Shores
May become unstable and prong to undercutting or to long-chore erosion and
May be lost through rill, gully or shoot erosion, may become prong to rapid
leaching of nutrients; may have rapid initial lose of organic matter, follow d by
stabilization as soil organisms responsible for decay decrease in numbers; may become
indurated as a result of laterization; micro-flora bad fauna may decrease or may be
altered through exposure to full sunlight; in turn, changes in micro-organismic life may
detrimentally affect decomposition and nutrient transfer; disappearance of mycorrhizae
may, in particular, retard or prevent the re-establishment of the many tree species that
feed symbiotically with these soil fungi; organic matter may increase under forest
plantations, with beneficial effects on soil structure, infiltration capacity,
soil-moisture holding capacity and cation-exchange capacity; accumulation of forest litter
under plantations may also increase the danger of fire. Plantations of certain species
may, on the other hand, detrimentally affect certain biophysical aspects of the soil (cf. Vegetation).
Soil structure, organic content and micro-organisms may be affected negatively by fire
used to clear forests for farming.
Sediment load in streams mad increase with adverse effects on channel stability,
navigation, fish spawning, bottom organisms (benthos), light penetration and other aspects
of aquatic life, accelerated sedimentation may shorten the useful lifespan of reservoirs;
on sloping ground, sediment from logged over areas may bury the roots of adjacent uncut
forest or the crops on nearby fields; re- and afforestation may decrease sediment loads
and thus reverse the negative effects described above.
Denuded slopes, compacted soils and decreased infiltration and canopy
interception may lead to larger volumes of storm runoff and to quicker responses of runoff
to precipitation; despite lower infiltration of rainfall, baseflow may increase locally
after de forestation owing to decreased transpiration; however, large-scale deforestation
usually results in lower down-basin low flows because of decreased infiltration and
groundwater recharge, greater storm runoff and increased evaporation; smaller discharges
may interfere with down-stream withdrawals for agriculture and domestic use. These effects
may be reversed with re- or afforestation.
Reforestation in semi arid regions may, however, locally deplete soil moisture,
lower water tables and result in decreased goundwater recharge and baseflow; this negative
effect may be in part off set by increased infiltration capacity of soils under forest.
In humid areas, logging may indirectly raise water tables locally as
transpiration is decreased; the use of heavy machinery may also cause local ponding of
water, which in turn can drown seedlings and otherwise injure plants. Logging, floating of
logs and improper disposal of slash and other organic debris may increase the turbidity
and phenolic content of surface waters, and may accelerate the eutrophication of these
waters through soil-nutrient losses and BOD loading of streams with debris; improper
storage and disposal of fuel, lubricants, wood preservatives and biocides may contaminate
surface and ground water.
Return water from irrigated tree plantations in semi arid areas may be saline;
excessive fertilization of plantations may accelerate the eutrophication of waters.
Climate and Air Quality
Logging may increase ground temperatures and lower atmospheric humidity locally
which, in turn, may interfere with seedling growth and micro-organismic life in the soil;
large-scale deforestation may cause regional desiccation of the climate as transpiration
is decreased, and local convection patterns are altered by changes in surface roughness
and albedo; changes in the balance between sensible and latent heat (Bowen ratio) may,
cumulatively affect global circulation patterns.
Logging in semi-arid regions or seasonally dry regions may release dust into the
air; bare soils may become prone to wind deflation; tree felling, log hauling and other
uses of machinery may release fumes; saw-milling, charcoal making and other wood
transformation may cause local particulate and other emissions; large-scale deforestation
may, cumulatively affect the global CO2 balance, as tropical forests represent
massive CO2 fixation; although the recent increase in atmospheric CO2
does not seem to be related to deforestation, there is need for caution before under
taking massive consumption (burning, decay) of tropical wood. Deforestation has apparently
a negligible effect on the global O2 balance, presumably so long as the total
surface of land vegetation remains essentially unchanged.
Moist tropical high forest may not regenerate itself at all after clear-cutting.
Clear-cutting may eliminate entire endemic species or substantial portions of the total
gene pool of certain species, including timber species. Total forest removal in areas of
high species diversity increases the likelihood of loss of species and of genetic
resources. On the other hand, clear-cutting and replacement of the natural forest with
highly productive plantations can mean that fewer inroads are made into natural forests
elsewhere. Selective logging of superior trees men cause genetic erosion. It may also
damage much of the residual vegetation; seed trees may not survive because of
"isolation shock" or because of mechanical damage during logging. Simplification
of the forest through selective cutting or enrichment plantings with few species may
reduce the overall resilience of the forest to pests and pathogens. On the other hand, the
removal of over-mature, mature and defective trees may "release" other trees,
there by increasing the health and productivity of the forest. Defective trees, such as
hollow trees, may, however, be ecologically valuable (cf. Wildlife). Logging may,
indirectly make adjacent uncut forests more vulnerable to windthrow, fire, illegal felling
and shifting cultivation; alteration of the local hydrology and root burial by sediment
may also affect adjacent vegetation adversely. Adjacent or residual stands can suffer
mechanical damage during logging. The use of arboricides and other biocides may interfere
with seedling growth, damage crops and adversely affect animal life, including human
reproduction. Deforestation (land clearance for agriculture) by means of fire (or in areas
unsuited for this technique) can damage residual vegetation, as well as soils, wildlife
and fisheries. Plantations of certain species may detrimentally change the pH, specific
nutrient status and micro-organismic life of soils, while improving organic content,
structure and cation-exchange capacity of soils. Plantations of conifers may be especially
prone to forest fires; they may require fire roads (10-12 m wide) and fire strips. Forest
removal and replacement with exotics may deprive some animal species of food and shelter,
and may attract and harbour some pests. Shelterbelt plantings in semi-arid areas may have
the desired micro-climatic effects, but may also have negative side-effects such as root
invasion of adjacent crop lands and of irrigation drainage tiles. Shelterbelts may waste
water intended for crops by withdrawing water from irrigation ditches.
Wildlife and Fisheries
Logging can injure and kill some animals outright, but more likely it damages or
destroys key habitats such as nesting sites, including old hollow trees, feeding and
breeding grounds. It can also interrupt or eliminate the aerial pathways of arboreal
species that seldom move at ground level. Some endemic species of animals could be
Erosion, sedimentation or improper slash and other waste disposal can damage or
destroy fish spawning and nursery areas, benthic communities and other important aquatic
habitats and organisms. Turbidity can interfere with light penetration and thereby
decrease the rates of photosynthesis and of overall productivity of aquatic ecosystems.
Removal of tree cover adjacent to streams and rivers can raise the temperature of water to
levels injurious to aquatic organisms adapted to stenothermal conditions. Log floating can
interfere with commercial and subsistence fisheries by damaging fishing gear, aquatic
habitats and by contaminating waters with wood preservatives. Log and log hauling can
displace animals through noise and increased human presence; some of these animals,
particularly if highly territorial, cannot easily occupy adjacent undisturbed forests.
Displaced animals added to existing populations can mean crowding, with related stress and
decrease in reproductive rates.
The elimination of some herbivores, birds or insects through logging can
interfere with the regeneration of tree and other plant species that depend on these
animals for pollination or seed dispersal. Elimination of some insect populations could
retard the digestion of vegetal matter and, hence, nutrient recycling. Clear-out areas and
forest roads create new access which, if uncontrolled, can load to excessive hunting or
poaching in hitherto inaccessible areas.
Logging can create favourable new browse or habitats for some animals, notably
some wild cattle, other ungulates and rodents. Some herbivores, especially elephants, can
be displaced and made dependent on agricultural crops, with resultant economic losses. The
new habitats created by logging can result in the explosive growth of some animal
populations, primarily rodents, some herbivores and some insects. These animals can, in
turn, adversely affect forest regeneration or nearby crops. Some of these animals can be
vectors for diseases.
Local Cultures and Subsistence Economies
Forestry projects can substantially and permanently improve the living standards
of local residents through direct and indirect employment in a new cash economy, new
roads, housing, medical facilities and other new infrastructure.
However, the transition from a non-gash to a cash economy and from a traditional
life-style to a more modern one may or may not be the desired goal of most local
residents. If the preservation of a subsistence economy is the expressed wish of the local
population, then forestry activities can have a number of detrimental effects. Thus,
logging can eliminate or reduce the habitat, food and other traditional resources of
forest dwellers. In remote areas, logging operations and the attendant influx of outsiders
and new ways can lead to "culture shook" and related social disintegration. At
worst, it can lead to violent conflict. Logging can inadvertently or other wise damage or
destroy trace, sites or other landscape elements that have religious or other heritage
value. It can disturb burial grounds a and historic or archaeological sites.
The elimination of traditional food and other supplies, the creation of new
demands, or the introduction of fossil fuels and other consumer item can disrupt a local
non-cash economy, thereby causing social upset. Deforestation can decrease the local
fuelwood supply and thus make residents dependent on substitute energy sources, with
regional or even national repercussions. Afforestation or reforestation can reverse this
trend. Forestry activities can raise employment and other socio-economic expectations
among people who wish to leave the non-cash economy; these expectations, if not met, can
lead to conflict. Logging and improved access can increase the extent and intensity of
shifting cultivation, with resultant degradation of soils, vegetation and other resources.
Forestry projects can stimulate the local cash economy through direct and
indirect employment and increased demand for goods and services. These projects can also
result in improved facilities, such as new or better roads, medical facilities, schools
etc. Balanced against these benefits may be the need to clear additional forest for
logging camps, new settlements, roads and other facilities. If poorly regulated logging
camps can be a source of friction with local residents. Improper waste disposal and
harassment of wildlife are often associated with temporary camps. The same applies on a
larger scale to new settlements created by the influx of people directly or indirectly
employed in the forestry sector.
In general, more people mean more roads, schools, waterworks, liquid and solid
waste disposal and other facilities that may create jobs but also overtax local financial
and trained manpower resources. Greater concentrations of people and economic activity
also mean pressures on the local and regional environment (demand for recreational space,
degradation of air and water quality, inroads into animal habitats, etc.). The demand for
public services (education, health, government) is also likely to increase; this can have
benefits such as job creation, but also negative impacts if the necessary trained manpower
is not available.
Expansion of forestry activities may conflict with or complement other economic
land uses such as agriculture, mining or tourism (cf. Conservation).
Forest removal may increase the rates of incidence of certain diseases or
introduce new diseases such as malaria (through exposure of stagnant water previously
under forest cover) and scrub typhus (creation of Imperata grasslands invaded by
rodents). Any water impoundment associated with forestry could lead, in certain regions,
to outbreaks of schistosomiasis or onchocerciasis. Destruction of forests may bring forest
arthropod vectors of arbovirus diseases into closer contact with man. On the other hand,
clearing of riparian forest is used to control trypanosomiasis. The influx of forest
workers and outsiders may increase the incidence of certain diseases such as
trypanosomiasis or sexually transmitted diseases. On the other hand, medical facilities
and standards established in connection with forestry projects can significantly improve
local or regional health conditions.
It is conceivable that, with deforestation and/or penetration of agriculture into
forested areas, domestic animals become the hosts of parasite cycles previously hosted by
Forestry activities may conflict with existing, planned or potential conservation
areas (protection forests, parks, game reserves, strict nature reserves, sanctuaries).
Logging could affect conservation areas of vague legal status or that are poorly delimited
on the ground. Forestry activities in the buffer zones around conservation areas may have
indirect detrimental effects (sedimentation; displacement of animals through noise and
human presence; increased poaching due to new access). Logging can undermine conservation
plans if it takes place while these plans are being held up by administrative or
Turbidity in streams dead trees, swaths of clear-cut areas, accumulations of
slash and other debris, hanging debris, road traffic from logging areas, noise, dust and
other side effects of forestry can detract from the amenity value of a region.
On the other hand, well planned forest roads can subsequently be used for tourist
and other amenity uses, as well as for enforcing conservation laws.
Re- or afforestation, especially if done from a multiple purpose standpoint, can
add to the amenity value of a region, either through improved aesthetics, the provision of
recreational spaces or climatic improvement. Plantings in bare or eroded landscapes
greatly improve the appearance of those landscapes, in addition to providing many other
environmental benefits. However, plantations that are too regular or uniform in species
composition can be a visual liability.
Cut-over areas or monotonous plantations well outside conservation arose such as
national parks can detract from vistas that are appreciated from points within those
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