Environmental Problems, Their Causes, and Sustainability 1

and degradation practices, Brazil’s original Amazonrain forests may largely disappear within 40–50 years.You probably have not heard about the loss ofmost of Brazil’s Atlantic coastal rain forest. This less famousforest once covered about 12% of Brazil’s landarea. Now 93% of it has been cleared and most of whatis left is recovering from previous cutting episodes.This represents a major loss of biodiversity because anarea in this forest a little larger than two typical suburbanhouse lots in the United States has 450 tree species!The entire United States has only about 865 native treespecies.There are disagreements about how rapidly tropicalforests are being deforested and degraded becauseof three factors. First, it is difficult to interpret satelliteimages. Second, some countries hide or exaggerate deforestationrates for political and economic reasons.Third, governments and international agencies defineforest, deforestation, and forest degradation in differentways.For these reasons, estimates of global tropical forestloss vary from 50,000 square kilometers (19,300 squaremiles) to 170,000 square kilometers (65,600 squaremiles) per year. This is high enough to lose or degradehalf of the world’s remaining tropical forests in 35–117years.Most biologists believe that cutting and degradingmost remaining old-growth tropical forests is a seriousglobal environmental problem because of the importantecological and economic services they provide(Figure 11-7). For example, tropical forest plants providechemicals used as blueprints for making most ofthe world’s prescription drugs (Figure 11-17). And cuttingthese forests faster than they can grow back contributesto projected global warming because theseforests are a storehouse for huge quantities of carbon,safely stored as organic compounds in plant biomass.What Causes Tropical Deforestation andDegradation? The Big FiveThe primary causes of tropical deforestation anddegradation are population growth, poverty, environmentallyharmful government subsidies, debtsowed to developed countries, and failure to valueecological services.Tropical deforestation results from a number of interconnectedprimary and secondary causes (Figure11-18, p. 212). Population growth and povertycombine to drive subsistence farmers and the landlesspoor to tropical forests, where they try to grow enoughfood to survive. Government subsidies can acceleratedeforestation by making timber or other tropical forestresources cheap, relative to the economic value of theecological services they provide. Governments in Indonesia,Mexico, and Brazil also encourage the poor tocolonize tropical forests by giving them title to landthey clear. This can help reduce poverty but can lead toRauvolfiaRauvolfia sepentina,Southeast AsiaTranquilizer, highblood pressuremedicationPacific yewTaxus brevifolia,Pacific NorthwestOvarian cancerFoxgloveDigitalis purpurea,EuropeDigitalis for heart failureCinchonaCinchona ledogeriana,South AmericaQuinine for malaria treatmentRosy periwinkleCathranthus roseus,MadagascarHodgkin's disease,lymphocytic leukemiaFigure 11-17 Natural capital: nature’s pharmacy. Parts of these and a number of other plants and animals(many of them found in tropical forests) are used to treat a variety of human ailments and diseases. Nine of theten leading prescription drugs originally came from wild organisms. About 2,100 of the 3,000 plants identifiedby the National Cancer Institute as sources of cancer-fighting chemicals come from tropical forests. Despitetheir economic and health potential, fewer than 1% of the estimated 125,000 flowering plant species in tropicalforests (and a mere 1,100 of the world’s 260,000 known plant species) have been examined for their medicinalproperties. Once the active ingredients in the plants have been identified, they can usually be produced synthetically.Many of these tropical plant species are likely to become extinct before we can study them.Neem treeAzadirachta indica,IndiaTreatment of manydiseases, insecticide,spermicidehttp://biology.brookscole.com/miller14211