Environmental Problems, Their Causes, and Sustainability 1

food and urban development. Chaparral and thornscrub, temperate grasslands, temperate rain forests,and tropical dry forests have also been greatly disturbedby human activities. Tundra, tropical deserts,and land covered with ice are the least disturbed biomesbecause their harsh climates and poor soils makethem unappealing to most human activities.In the United States, at least 95% of the virginforests in the lower 48 states have been logged for lumberand to make room for agriculture, housing, andindustry. In addition, 98% of tallgrass prairie in theMidwest and Great Plains has disappeared, and 99%of California’s native grassland and 85% of its originalredwood forests are gone.By some estimates, humans use, waste, or destroyabout 10–55% of the net primary productivity of theplanet’s terrestrial ecosystems. And biologists estimatethat the current global extinction rate of species is atleast 100 times and probably 1,000 to 10,000 timeswhat it was before humans existed.These threats to the world’s biodiversity are projectedto increase sharply by 2018 (Figure 11-4). Studythis figure carefully.Figure 11-5 outlines the goals, strategies, and tacticsfor preserving and restoring the earth’s terrestrialecosystems (as discussed in this chapter) and preventingthe premature extinction of species (as discussed inChapter 12). Sustaining aquatic diversity is discussedin Chapter 13.Why Should We Care About Biodiversity?Sustaining a Vital Part of the World’s LifeSupport SystemBiodiversity should be protected from degradationby human activities because it exists and becauseof its usefulness to us.Biodiversity researchers contend that we should act topreserve the earth’s overall diversity because its genes,species, ecosystems, and ecological processes havetwo types of value. One is intrinsic or existence valuebecause these components of biodiversity exist, regardlessof their use to us.The other is instrumental value because of theirusefulness to us. There are two major types of instrumentalvalues. One consists of use values that benefit usin the form of economic goods and services, ecologicalservices, recreation, scientific information, and preservingoptions for such uses in the future.Another type consists of nonuse values. One is theexistence value in knowing that a redwood forest,wilderness, or endangered species exists, even if wewill never see it or get direct use from it. Aesthetic valueis another nonuse value because many people appreciatea tree, forest, wild species, or a vista because of itsbeauty. Bequest value is a third type of nonuse value. Itis based on a willingness of some people to pay toprotect some forms of natural capital for use by futuregenerations.Arctic Circle30°N60°NORTHAMERICAEUROPEASIATropic Of CancerPacificOceanAtlanticOceanAFRICAPacificOcean0°150° 120° 90° 30°W 0° 60°E 90°150°Tropic Of Capricorn30°SSOUTHAMERICAIndianOceanAUSTRALIA60°Antarctic CircleANTARCTICAProjected Status of Biodiversity1998–2018Critical and endangeredThreatenedStable or intactFigure 11-4 Natural capital degradation: projected status of the earth’s biodiversity between 1998 and 2018.(Data from World Resources Institute, World Conservation Monitoring Center, and Conservation International)196 CHAPTER 11 Sustaining Terrestrial Biodiversity: Managing and Protecting Ecosystems