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4. Materials and Energy
Pages 61-67

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From page 61...
... Human societies depend on harvesting organisms or parts of them, so many of our perturbations of ecosystems are intended to maintain or increase production of organisms. Methods of increasing production of organisms useful to people include domestication, increasing the proportion of production that comes from species of economic value, removing predators, reducing competition, and increasing supplies of the resources that support production (e.g., by fertilization, irrigation, and modification of microclimates)
From page 62...
... in forests generally increases as solar energy available during the growing season decreases that suggests the increasing importance of energy storage in low-energy environments. · The ratio of wood production to litter production decreases as precipitation decreases that suggests that increases in size are less valuable than the production of photosynthetically active tissue in dry environments.
From page 63...
... Common physical perturbations are those imposed deliberately in land management, e.g., logging or selective harvesting of forests (Chapters 19 and 23) , channeling or damming to alter water flow (Chapter 21)
From page 64...
... Changes in global biogeochemical cycles affect environmental problem-solving at specific sites and are beyond the control of managers. But they are the most important of the cumulative effects of individual projects, because the perturbations are largely the sum of the inputs of specific projects.
From page 65...
... Relationships between production and light are sometimes more important than those between production and nutrients. For example, Southern Indian Lake remained thoroughly mixed after impoundment, and suspended solids from an eroding shoreline increased abiotic turbidity and diminished light penetration (Chapter 21~.
From page 66...
... For single lake basins or lake districts, the fits are usually far better, particularly when variation in externally derived nutrient loading is large (Edmondson and Lehman, 1981; Schindler et al., 1978) , but even in such basins, changes in chlorophyll and water transparency can be extreme, despite relatively constant nutrient loads (Edmondson and Litt, 19824.
From page 67...
... The same problem is central in understanding the influence of human activities on global air circulation patterns and climate issues addressed only peripherally here. Changes in behavior of nutrients seldom attract attention, because they are often not directly perceivable by the unaided senses, although they do become obvious, for example, when they impair visibility in scenic areas.


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