Environmental Problems, Their Causes, and Sustainability 1

4540HarpyeagleEmergentlayer35Tocotoucan30CanopyHeight (meters)252015WoolyopossumUnderstory105BraziliantapirShrublayer0Black-crownedantpittaGroundlayerFigure 6-30 Natural capital: stratification of specialized plant and animal niches in various layers of a tropicalrain forest. The presence of these specialized niches enables species to avoid or minimize competition for resourcesand results in the coexistence of a great variety of species.Dropped leaves, fallen trees, and dead animals decomposequickly because of the warm, moist conditionsand hordes of bacteria, fungi, insects, and otherdetritivores. This rapid recycling of scarce soil nutrientsis why little litter is found on the ground. Instead of beingstored in the soil, most nutrients released by decompositionare taken up quickly and stored by trees,vines, and other plants. This explains why tropical rainforest soils have so few plant nutrients (Figure 4-27,bottom left, p. 75). Because of their poor soils, these arenot good places to clear and grow crops or graze cattle.What Are Temperate Deciduous Forests?Seasonal Changes and Beautiful ColorsMost of the trees in these forests survive winter bydropping their leaves, which decay and producea nutrient-rich soil.Temperate deciduous forests grow in areas with moderateaverage temperatures that change significantly withthe season. Trace the nutrient transfers and energyflows in Figure 6-31 (p. 123). These areas have long,warm summers, cold but not too severe winters, andabundant precipitation, often spread fairly evenlythroughout the year (Figure 6-28, center).This biome is dominated by a few species ofbroadleaf deciduous trees such as oak, hickory, maple,poplar, and beech. They survive cold winters by droppingtheir leaves in the fall and becoming dormant.Each spring they grow new leaves that change in thefall into an array of reds and golds before dropping.Temperate deciduous forests have fewer treespecies than tropical rain forests. But the penetrationof more sunlight supports a richer diversity of plantlife at ground level. Because of the fairly low rate ofdecomposition, these forests accumulate a thick layer122 CHAPTER 6 Climate and Terrestrial Biodiversity