Environmental Problems, Their Causes, and Sustainability 1

Terrestrial EcosystemsSwamps and marshesTropical rain forestTemperate forestNorthern coniferous forest (taiga)SavannaAgricultural landWoodland and shrublandTemperate grasslandTundra (arctic and alpine)Desert scrubExtreme desertAquatic EcosystemsEstuariesLakes and streamsContinental shelfOpen ocean800 1,600 2,400 3,200 4,000 4,800 5,600 6,400 7,200 8,000 8,800 9,6002Average net primary productivity (kcal/m /yr)Figure 4-24 Natural capital: estimated annual average net primary productivity (NPP) per unit of area inmajor life zones and ecosystems, expressed as kilocalories of energy produced per square meter per year(kcal/m 2 /yr). (Data from Communities and Ecosystems, 2nd ed., by R. H. Whittaker, 1975. New York:Macmillan)dispersed, tiny floating producers in the open oceanwould take much more fossil fuel and other types ofenergy than the food energy we would get. In addition,this would disrupt the food webs of the openocean that provide us and other consumer organismswith important sources of energy and protein fromfish and shellfish.How Much of the World’s Net Rate ofBiomass Production Do We Use? Let ThemEat CrumbsHumans are using, wasting, or destroying a significantamount of the world’s biomass faster than producerscan make it.Peter Vitousek, Stuart Roystaczer, and other ecologistsestimate that humans now use, waste, or destroy about27% of the earth’s total potential NPP and 10–55% ofthe NPP of the planet’s terrestrial ecosystems.These scientists contend that this is the main reasonwe are crowding out or eliminating the habitatsand food supplies of a growing number of otherspecies. What might happen to us and to other consumerspecies if the human population doubles overthe next 40–50 years and per capita consumption of resourcessuch as food, timber, and grassland risessharply? This is an important question!4-6 SOILSWhat Is Soil and Why Is It Important?The Base of Life on LandSoil is a slowly renewed resource that providesmost of the nutrients needed for plant growth andalso helps purify water.Soil is a thin covering over most land that is a complexmixture of eroded rock, mineral nutrients, decayingorganic matter, water, air, and billions of living organisms,most of them microscopic decomposers. Studythe diagram in Figure 4-25 showing the profile of differentaged soils. Soil is a renewable resource but it isrenewed very slowly. Depending mostly on climate,the formation of just 1 centimeter (0.4 inch) of soil cantake from 15 years to hundreds of years.Soil is the base of life on land because it providesmost of the nutrients needed for plant growth. Indeed,you are mostly soil nutrients imported into your bodyby the food you eat. Soil is also the earth’s primary filterthat cleanses water as it passes through. It is also a72 CHAPTER 4 Ecosystems: What Are They and How Do They Work?