If soil, water, light and air play a major role in the life of the tree, the forest does not just use the resources of nature in its favor. In return, it also renders valuable services to its environment. Improvement of air and water quality, prevention of soil erosion, source of food and habitat for animals, noise reduction … without counting on its other economic functions, tourism and enhancement of landscapes.
During the chlorophyll assimilation process, the tree absorbs carbon dioxide and releases oxygen. The forest functions as a carbon sink and contributes to the Kyoto Protocol targets to reduce greenhouse gases due to human activity.
Annually, one hectare of forest assimilates 5 to 10 tons of carbon and releases 10 to 20 tons of oxygen.
In comparison, during the same period, man consumes about 300 kg of oxygen while a jet plane burns 35 tonnes to cross the Atlantic! It must be added that the tree also breathes and that it then absorbs oxygen and rejects carbon dioxide. But the global balance of these exchanges is largely beneficial for the man.
The forest also intervenes in air quality by filtering dust and microbial pollution resulting from industrial activity. In this role of the plant, the vitality of the forest is an indicator of health.
The forest participates in the regulation of the water cycle thanks to its behavior during periods of precipitation.
All the rain does not reach the ground. A portion is intercepted by the leaf area and evaporates substantially at this level.
The rest drips or flows along the trunks and branches … or directly reaches the litter and soil humus. When these two horizons are saturated, the water, filtered from its impurities by percolation through the different strata of the soil, travels towards the water table and ensures the supply of the sources.
Prevention of soil erosion
Soil and water erosion is a threat to all lands, especially when the terrain is sloping, easily flooded or exposed to the wind.
By intercepting the rain thanks to the cover of the leaves, the forest dampens the violence of the precipitations and thus prevents the erosion of the ground by gully. It plays the same role of retarder for wind and desertification. In France, dune fixation by vegetation and forest fence is used on the Atlantic coast.
In the case of deforestation, soil erosion on sloping terrain, especially in the middle mountains, can take on worrying proportions. In areas subject to frequent and intense rains, rich vegetation (trees, shrubs, grasses, mosses) limits the erosion and leaching effect of the soil. This beneficial role is even more important if the terrain has long, steep slopes and soils do not readily absorb water as in the mountains.
Finally, the forest represents an obstacle to reduce the effects of avalanches. Reforestation of degraded lands in the mountains helps prevent floods and avalanches.
This effect is related to the structure and density of forest stands. The forest absorbs and dampens the noise pollution associated with urbanization.
On the surface, plant and animal deposits form litter and humus. They are transformed thanks to an intense microbial activity which contributes to the fertility of the soil. This action is continued, more deeply, by the roots which, by cracking the hard rocks, create migration corridors for air and water.