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Chico Mendes : non à la déforestation Collombat Isabelle Neuf Livre
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1935.autographe Deffontaines.forêt équatoriale.écologie déforestation
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De la déforestation due à l'Homme dès les années -3000 en Afrique

Feb 23, 2012
, Des chercheurs français ont trouvé dans le bassin du Congo les traces sédimentaires d’une brusque accélération du remplacement des forêts par les savanes, survenue il y a 3.000 ans et probablement due au défrichage pratiqué par les premiers agriculteurs. 

C'est en analysant les ratios entre quantités d’argile, d’aluminium et de potassium dans des carottes de sédiments déposés il y a 20.000 à 3.000 ans, prélevées récemment dans l’embouchure du fleuve Congo que les chercheurs ont fait leur découverte. L'équipe de l’Ifremer dirigée par Germain Bayon a constaté, à partir de -3.500 ans, une érosion (avec un pic vers -2.500 ans) qui ne peut être due aux seules précipitations.

Selon les chercheurs, cette érosion est signe d’un remplacement de la forêt par la savane, lui-même confirmé par l’abondance de pollen de graminées dans les couches sédimentaires de cette même époque. Or, c’est à ce moment-là précis que les populations bantoues d’Afrique occidentale ont migré vers l’Afrique centrale.

Ainsi, les chercheurs interprètent cette érosion accrue comme la conséquence d’une déforestation possible, pratiquée par ces agriculteurs pour dégager de nouvelles surfaces cultivables. Défrichage, ruissellement, érosion, un enchaînement bien connu des géologues aujourd'hui... Toutefois, il est difficile d’estimer la part de cette action humaine et celle du réchauffement climatique naturel (de l’époque) dans ce processus.

Source: Maxisciences

La déforestation

Feb 23, 2012

Au Québec, l'exploitation des ressources naturelles est un grand atout pour l'économie. L'un de ses volets, l'exploitation forestière, rapporte beaucoup à notre province depuis longtemps. Bien que ce domaine économique soit payant, il entraine un phénomène dévastateur qui touche la population mondiale, la déforestation. 

 

Selon le World Ressources, 80% de la couverture mondiale originale a été abattue ou dégradée, essentiellement au cours des 30 dernières années. En effet, notre planète a perdu en moyenne 4,9 millions d'hectares de forêt par an, soit près de 10 hectares de forêt par minute ou encore l'équivalent d'un terrain de football toutes les quatre secondes de 1990 à 2005 [1] . Ces statistiques alarmantes laissent place à plusieurs questionnements sur l'avenir de notre planète. Les arbres sont coupés infiniment plus vite que le rythme de régénération et de replantation. Cette gestion non durable laisse donc transparaître un doute sur l'avenir de nos forêts. 

Cette exploitation incontrôlable détruit de nombreux refuges et sources d'alimentation. On estime que 27 000 espèces animales et végétales disparaissent à cause des coupes à blanc et du manque de gestion des forêts. Aussi, le climat est affecté par la déforestation. En effet, 40 % du carbone de la terre est stocké dans les sols des forêts et la végétation [2] . Quand la forêt disparaît, le carbone qu'elle emmagasinait est majoritairement libéré dans l'atmosphère, ce qui augmente l'effet de serre, et par conséquent, le réchauffement climatique. La déforestation rend également les sols improductifs, ce qui empêche d’autres végétaux d'y pousser. En plus de tout cela, les forêts jouent un rôle essentiel dans le cycle de l'eau. Les arbres régularisent l'eau et l'emmagasinent. Si nos forêts disparaissent, il y a de grandes chances que nos rivières se volatilisent également.

Source: AgoraVox

La Déforestation de l'Amazonie Brésilienne

Tpe2008-2009. 1ereEs

Alternatives Sud, N° 15-2008 / 3 : Déforestation : Causes, acteurs et enjeux

Editions Syllepse

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Private or Socialistic Forestry?: Forest Transition in Finland Vs. Deforestation in the Tropics

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Deforestation and Climate Change

Congressional Research Service

Product Description

Efforts to mitigate climate change have focused on reducing carbon dioxide (CO2) emissions into the atmosphere. Some of these efforts center on reducing CO2 emissions from deforestation, since deforestation releases about 17% of all annual anthropogenic greenhouse gas (GHG) emissions and is seen as a relatively low-cost target for emissions reduction. Policies aimed at reducing deforestation are central points of a strategy to decrease carbon emissions, reflected in pending legislation in Congress (e.g., H.R. 2454 and S. 1733) as well as in international discussions, such as the December 2009 negotiations in Copenhagen.

Forests exist at many latitudes. Many are concerned about the possible impacts of losing boreal and temperate forests, but existing data show little, if any, net deforestation, and their loss has relatively modest carbon consequences. In contrast, tropical deforestation is substantial and continuing, and releases large amounts of CO2, because of the carbon stored in the vegetation and released when tropical forests are cut down.

There are many causes of tropical deforestation—commercial logging, large-scale agriculture (e.g., cattle ranching, soybean production, oil palm plantations), small-scale permanent or shifting (slash-and-burn) agriculture, fuelwood removal, and more. Often, these causes combine to exacerbate deforestation; for example, commercial logging often includes road construction, which in turn opens the forest for subsistence farmers. At times, tropical deforestation results from weak land tenure and/or weak or corrupt governance to protect the forests.

Congress and international bodies are discussing various policies to reduce carbon emissions from deforestation and forest degradation (REDD). Reducing deforestation in the tropics is likely to have additional benefits as well, such as preserving biological diversity and sustaining livelihoods for the rural poor and for indigenous communities and cultures. Proposals may be adapted to address local and regional causes of deforestation. Various forestry practices can reduce the impacts of deforestation, and several market approaches are evolving to compensate landowners for preserving their forests.

Many challenges remain for implementing REDD programs, particularly internationally, including monitoring REDD projects and improving developing-country capacity to ensure compliance. Existing evidence on forests and deforestation suggest the difficulties might be significant. Measuring forests is complicated, with multiple definitions, inaccessible sites, and expensive, complicated, and imperfect measurement technologies.

This report provides basic information on forests and climate change. The first section discusses the linkages between forests and climate. The next three describe the characteristics of the three major forest biomes, with an overview of deforestation causes and impacts. This is followed by an overview of approaches to reducing deforestation. The final section examines issues related to forest and deforestation data.
Efforts to mitigate climate change have focused on reducing carbon dioxide (CO2) emissions into the atmosphere. Some of these efforts center on reducing CO2 emissions from deforestation, since deforestation releases about 17% of all annual anthropogenic greenhouse gas (GHG) emissions and is seen as a relatively low-cost target for emissions reduction. Policies aimed at reducing deforestation are central points of a strategy to decrease carbon emissions, reflected in pending legislation in Congress (e.g., H.R. 2454 and S. 1733) as well as in international discussions, such as the December 2009 negotiations in Copenhagen.

Forests exist at many latitudes. Many are concerned about the possible impacts of losing boreal and temperate forests, but existing data show little, if any, net deforestation, and their loss has relatively modest carbon consequences. In contrast, tropical deforestation is substantial and continuing, and releases large amounts of CO2, because of the carbon stored in the vegetation and released when tropical forests are cut down.

There are many causes of tropical deforestation—commercial logging, large-scale agriculture (e.g., cattle ranching, soybean production, oil palm plantations), small-scale permanent or shifting (slash-and-burn) agriculture, fuelwood removal, and more. Often, these causes combine to exacerbate deforestation; for example, commercial logging often includes road construction, which in turn opens the forest for subsistence farmers. At times, tropical deforestation results from weak land tenure and/or weak or corrupt governance to protect the forests.

Congress and international bodies are discussing various policies to reduce carbon emissions from deforestation and forest degradation (REDD). Reducing deforestation in the tropics is likely to have additional benefits as well, such as preserving biological diversity and sustaining livelihoods for the rural poor and for indigenous communities and cultures. Proposals may be adapted to address local and regional causes of deforestation. Various forestry practices can reduce the impacts of deforestation, and several market approaches are evolving to compensate landowners for preserving their forests.

Many challenges remain for implementing REDD programs, particularly internationally, including monitoring REDD projects and improving developing-country capacity to ensure compliance. Existing evidence on forests and deforestation suggest the difficulties might be significant. Measuring forests is complicated, with multiple definitions, inaccessible sites, and expensive, complicated, and imperfect measurement technologies.

This report provides basic information on forests and climate change. The first section discusses the linkages between forests and climate. The next three describe the characteristics of the three major forest biomes, with an overview of deforestation causes and impacts. This is followed by an overview of approaches to reducing deforestation. The final section examines issues related to forest and deforestation data.