Ecological Knowledge and Environmental Problem-Solving Concepts and Case Studies (1986) / Chapter Skim
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9. The Special Problem of Cumulative Effects
9. The Special Problem of Cumulative Effects
Pages 93-103
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From page 93... ...
Recent awareness of such serious cumulative effects as acid rain, the rapid loss of tropical forests, and the threatened extinction of many species has brought increasing political and scientific attention to cumulative environmental effects. Many cumulative effects result from the movement of materials through the environment.
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From page 94... ...
A step toward identifying the major issues involved in the assessment of cumulative impact was made in a recent international workshop held in Toronto, Ontario, under the joint sponsorship of the present committee and the Canadian Environmental Assessment Research Council. Some of this chapter draws on the proceedings of the Toronto workshop (Beanlands et al., in press)
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From page 95... ...
The effect of harvest rate on population dynamics is seldom a linear function of population density, and the response of a population to an incremental increase in harvesting rate can vary substantially with conditions. Increasing the intensity of harvesting can lead to population collapse if a critical threshold is passed, especially if the increase in harvesting is combined with natural environmental changes (Beverton, 1983; Murphy, 1977; Parrish and MacCall, 1978; Peterman, 19781.
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From page 96... ...
Sometimes, repeated attempts to "improve" the environment have the greatest cumulative effects of all. The conversion of deserts to arable land by massive irrigation projects destroys desert habitats, but creates economic benefits and new habitats that favor species adapted to exploit irrigated farmland.
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From page 97... ...
DIFFICULTIES IN PREDICTING AND CONTROLLING CUMULATIVE EFFECTS A fundamental problem in predicting and controlling cumulative effects is the frequently large mismatch between the scales or jurisdictional boundaries of management authority and the scales of the ecological phenomena involved or their effects. Affected environments such as river basins, airsheds, and estuaries usually cross local and state, and sometimes even national, boundaries.
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From page 98... ...
SCALE AND THE RATES OF CRITICAL PROCESSES Choosing appropriate scales on which to analyze cumulative effects requires an understanding of the relative balance of important concentrating and dispersing phenomena and of the rates of other processes that influence the removal of or recovery from individual stresses in the environment being studied (see also Chapter 51. Because the rate of atmospheric mixing is so high and because the atmosphere is relatively uncompartmentalized, many materials that have low rates of removal from
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From page 99... ...
The sizes of habitat patches and the distance between them can profoundly influence the survival of species that depend on them. The probability of local extinction increases as population size decreases, and the chance that a given habitat patch will be recolonized depends on the dispersibility of the species, the proximity of sources of potential colonizers, and the ability of a population to be established by a small number of colonizing individuals (Chapters 1 and 51.
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From page 100... ...
. The approach is designed to identify the many kinds of perturbations that affect particular valued atmospheric components and the multiple effects of particular perturbations through an analysis of the mechanisms of interaction that underlie direct and indirect pathways of cause and effect.
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From page 101... ...
The most critical immediate need in management practices identified in the workshop was the need to improve the match in scales between the ecological phenomena involved in cumulative effects and the management jurisdiction. A good start in this direction would be to improve communication between scientists and managers, and the nomogram used by Erdle and Baskerville (Chapter 19)
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From page 102... ...
For example, the formation of a metropolitan regulatory authority to control sewage pollution in Lake Washington was very effective, because the public readily comprehended the issues and agreed on the value of a clean lake (Chapter 204. The effort to establish regional control of multiple sources of pollution in the Delaware River Basin was much more complex (Ackerman et al., 1974~: many issues of conflict were involved, there was less public agreement on what was most valued, the scientific questions were more difficult, the regional authority was far less successful, and attempts to expand the scope of the metropolitan authority (like that formed to protect Lake Washington)
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From page 103... ...
In addition, monitoring should be frequent enough and carried out for long enough to detect cumulative effects. · Agreements between decision-makers, managers, and scientists with respect to the appropriate time and space boundaries for dealing with cumulative effects should be documented.
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