Environmental Problems, Their Causes, and Sustainability 1

Weak treesremovedFigure 11-8 Short (25- to 30-year)rotation cycle of cutting and regrowthof a monoculture tree plantationin modern industrial forestry. Intropical countries, where trees cangrow more rapidly year-round, therotation cycle can be 6–10 years.Clear cutforests to invasion by nonnative pests, diseases, andwildlife species. They also open once-inaccessibleforests to farmers, miners, ranchers, hunters, and offroadvehicle users. In addition, logging roads on publiclands in the United States disqualify the land forprotection as wilderness.Once loggers can reach a forest, they use variousmethods to harvest the trees (Figure 11-10, p. 202).With selective cutting, intermediate-aged or maturetrees in an uneven-aged forest are cut singly or insmall groups (Figure 11-10a). Selective cutting reducescrowding, encourages growth of younger trees, maintainsan uneven-aged stand of trees of differentspecies, and allows natural regeneration from surroundingtrees. It can also help protect the site fromsoil erosion and wind damage, remove diseased trees,and allow a forest to be used for multiple purposes.Sometimes loggers use a form of selective cuttingcalled high grading to selectively cut trees in many tropicalforests. It involves cutting and removing only the2530 Years of growth15105Seedlingsplantedlargest and best specimens ofthe most desirable species.Studies show that for everylarge tree cut down, 16 or 17other trees are damaged orpulled down because a networkof vines usually connectsthe trees in tropical forest canopies.This reduction of the forest canopycauses the forest floor to become warmer,drier, and more flammable and increases erosionof the forest’s thin and usually nutrient-poor soil.Some tree species grow best in full or moderatesunlight in medium to large clearings. Three majormethods are used to harvest such species. One is shelterwoodcutting, which removes all mature trees in anarea in two or three cuttings over a period of time (Figure11-10b).Another is seed-tree cutting where loggers harvestnearly all of a stand’s trees in one cutting butleave a few uniformly distributed seed-producingtrees to regenerate the stand (Figure 11-10c).The third approach is clear-cutting, which removesall trees from an area in a single cutting (Figure 11-10d).Figure 11-11 (p. 203) lists the advantages and disadvantagesof clear-cutting. Shelterwood and seed-tree cuttingare basically forms of clear-cutting carried out intwo or more phases.A clear-cutting variation that can provide a sustainabletimber yield without widespread destructionis strip cutting (Figure 11-10e). It involves clear-cuttingHighwayCleared plotsfor grazingHighwayOld growthCleared plotsfor agricultureFigure 11-9 Natural capital degradation: building roads into previously inaccessible forests paves the wayto their fragmentation, destruction, and degradation.http://biology.brookscole.com/miller14201