Environmental Problems, Their Causes, and Sustainability 1

EcologicalServicesSupport energyflow andchemical cyclingReduce soilerosionAbsorb andrelease waterPurify waterPurify airInfluence localand regionalclimateStoreatmosphericcarbonProvidenumerouswildlife habitatsNatural CapitalForestsEconomicServicesFuelwoodLumberPulp to makepaperMiningLivestock grazingRecreationJobsFigure 11-7 Natural capital: major ecological and economicservices provided by forests.A second type is a second-growth forest: a standof trees resulting from secondary ecological succession(Figure 8-12, p. 158). They develop after the trees in anarea have been removed by human activities (such asclear-cutting for timber or conversion to cropland) orby natural forces (such as fire, hurricanes, or volcaniceruption).A tree plantation, also called a tree farm, is a thirdtype (see photo on p. vi). It is a managed tract withuniformly aged trees of one species that are harvestedby clear-cutting as soon as they become commerciallyvaluable. They are then replanted and clear-cut againin a regular cycle (Figure 11-8).Currently, about 63% of the world’s forests aresecondary-growth forests, 22% are old-growth forests,and 5% are tree plantations (that produce about onefifthof the world’s commercial wood). Five countries—Russia,Canada, Brazil, Indonesia, and Papua,New Guinea—have more than three-fourths of theworld’s remaining old-growth forests. Logging threatensabout 39% of these forests. The rest are not threatenedmostly because of their remoteness, not becauselaws protect them.What Are the Major Types of ForestManagement? Simple Tree Plantationsand Diverse ForestsSome forests consist of one or two species ofcommercially important tree species that arecut down and replanted, and others containdiverse tree species harvested individually orin small groups.There are two forest management systems. One iseven-aged management, which involves maintainingtrees in a given stand at about the same age and size.In this approach, sometimes called industrial forestry, asimplified tree plantation replaces a biologically diverseold-growth or second-growth forest. The plantationconsists of one or two fast-growing and economicallydesirable species that can be harvested every6–10 years, depending on the species (Figure 11-8).A second type is uneven-aged management,which involves maintaining a variety of tree species ina stand at many ages and sizes to foster natural regeneration.Here the goals are biological diversity, longtermsustainable production of high-quality timber,selective cutting of individual mature or intermediateagedtrees, and multiple use of the forest for timber,wildlife, watershed protection, and recreation.The fate of the world’s remaining forests will bedecided mostly by governments, which own about80% of the remaining forests in developing countries.Governments in both developing and developedcountries are under conflicting pressures from thosewanting to log forests and convert them to agriculturalland and urban development and conservationistswho want to protect them—especially the world’s remainingold-growth forests.According to a 2001 study by the World WildlifeFund, intensive but sustainable management of as littleas one-fifth of the world’s forests—an area twice thesize of India—could meet the world’s current and futuredemand for commercial wood and fiber. This intensiveuse of the world’s tree plantations and some ofits secondary forests would leave the world’s remainingold-growth forest untouched.How Are Trees Harvested? Be Selectiveor Chop Them All DownTrees can be harvested individually from diverseforests, or an entire forest stand can be cut down inone or several phases.The first step in forest management is to build roadsfor access and timber removal. Even carefully designedlogging roads have a number of harmful effects(Figure 11-9). They include increased erosion and sedimentrunoff into waterways, habitat fragmentation,and biodiversity loss. Logging roads also expose200 CHAPTER 11 Sustaining Terrestrial Biodiversity: Managing and Protecting Ecosystems