Environmental Problems, Their Causes, and Sustainability 1

Here are two pieces of bad news. First, surveys bythe World Resources Institute (WRI) indicate that overthe past 8,000 years human activities have reduced theearth’s original forest cover by 20–50%.Second, surveys by the UN Food and AgriculturalOrganization (FAO) and the World Resources Instituteindicate that the global rate of forest cover loss duringthe 1990s was between 0.2% and 0.5% a year, and atleast another 0.1–0.3% of the world’s forests were degraded.If correct, the world’s forests are being clearedand degraded at an exponential rate of 0.3–0.8% a year,with much higher rates in some areas. Over four-fifthsof these losses are taking place in the tropics. The WorldResources Institute estimates that if current deforestationrates continue, about 40% of the world’s remainingintact forests will have been logged or converted toother uses within 10–20 years, if not sooner.Here are two pieces of good news. First, the totalarea of many temperate forests in North America andEurope has increased slightly because of reforestationfrom secondary ecological succession on cleared forestareas and abandoned croplands.Second, some of the cut areas of tropical foresthave increased tree cover from regrowth and plantingof tree plantations. But ecologists do not believe thattree plantations with their much lower biodiversityshould be counted as forest any more than croplandsshould be counted as grassland. According to ecologistMichael L. Rosenzweig, “Forest plantations are justcornfields whose stalks have gotten very tall andturned to wood. They display nothing of the majestyof natural forests.”xHOW WOULD YOU VOTE? Should there be a global effortto sharply reduce the cutting of old-growth forests? Cast yourvote online at http://biology.brookscole.com/miller14.How Much Are the World’s EcologicalServices Worth? Putting a Price Tag onMother Nature’s ServicesThe huge economic value of the ecological servicesprovided by the world’s forests and other ecosystemsis rarely counted in making decisions about how touse these ecosystems.Currently forests are valued mostly for their economicservices (Figure 11-7, right). But suppose we estimateand take into account the ecological services providedby forests (Figure 11-7, left). Then researchers say thatthe economic value of their long-term ecological serviceswould be much greater than their short-term economicservices.In 1997, a team of ecologists, economists, and geographersattempted to estimate the monetary worth ofthe earth’s natural ecological services (see top half ofback cover). According to this crude appraisal led byecological economist Robert Costanza of the Universityof Vermont, the economic value of income from theearth’s ecological services is at least $36 trillion peryear! This is fairly close to the $42 trillion value of all ofthe goods and services produced throughout the worldin 2004. To provide an annual natural income of $36trillion per year, the world’s natural capital would havea value of at least $500 trillion—an average of about$82,000 for each person on earth!Based on these estimates, biodiversity is the world’sbiggest financial asset. But unless this natural asset isgiven a financial value that is included in evaluatinghow we use forests and other ecological resources itwill be used unsustainably and destroyed or degradedfor short-term profit.To estimate the monetary values of the ecologicalservices provided by the world’s natural capital, theresearchers divided the earth’s surface into 16 biomes(Figure 6-16, p. 111) and aquatic life zones. They omitteddeserts and tundra because of a lack of data. Thenthey agreed on a list of 17 goods and services providedby nature and sifted through more than 100 studiesthat attempted to put a dollar value on such services inthe 16 different types of ecosystems.According to this appraisal, the world’s forestsprovide us with ecological services worth about $4.7trillion per year—equal in value to about one-tenth ofall of the goods and services produced in the worldin 2004.The researchers say their estimates could easily betoo low by a factor of 10 to 1 million or more. For example,their calculations included only estimates ofthe ecosystem services themselves, not the naturalcapital that generates them. They also omitted thevalue of nonrenewable minerals and fuels.They hope such estimates will call people’s attentionto three important facts. The earth’s ecosystemservices are essential for all humans and theireconomies, their economic value is huge, and they arean ongoing source of ecological income as long as theyare used sustainably.Why have we not changed our accounting systemto reflect these losses? One reason is that economicsavings provided by conserving nature benefit everyonenow and in the future, whereas profits made byexploiting nature are immediate and benefit a relativelysmall group of individuals. A second reason isthat many current government subsidies and tax incentivessupport destruction and degradation offorests and other ecosystems for short-term economicgain. We get more of what we reward.How Can We Manage Forests MoreSustainably? Making Sustaining ForestsProfitableWe can use forests more sustainably by including theeconomic value of their ecological services, harvesting204 CHAPTER 11 Sustaining Terrestrial Biodiversity: Managing and Protecting Ecosystems