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Biologic Markers of Air-Pollution Stress and Damage in Forests (1989) / Chapter Skim
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Establishing Cause-and-Effect Relationships
Pages 11-14

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From page 11...
... Experimental studies have been designed to investigate the effects of specific pollutants or combinations of pollutants on forests or trees and to test whether a particular pollutant might be a factor in damage observed in an existing stand or single tree. However, in a forested region subjected to a variety of air pollutants and natural stresses, the effects of each stress are not necessarily unique and identifiable.
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From page 12...
... A related problem was addressed by bacteriologist Robert Koch in the nineteenth century, when the germ theory of disease was gaining wide acceptance (Koch, 1876~. Koch pointed to the need for systematic and rigorous proof that a disease was caused by a particular organism.
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From page 13...
... . rungs Insects Nematodes Bacteria Viruses and related forms Parasitic plants Predators Lack of essential symbionts Chemical factors: Deficiencies or imbalances in essential nutrients Toxic elements Allelopathic chemicals Herbicides Air pollutants: Toxic gases Toxic aerosols Growth-altering chemicals Acid deposition leading to direct injury Atmospheric deposition of toxic particulates Human disturbances: Mechanical injury to individual trees Clearing of forests Burning of forests Physical disturbance of soil induced by: Excessive drainage or flooding Compaction Erosion by wind or water Removal or destruction of organic matter Mechanical disturbance of soil
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From page 14...
... The individual components of establishing cause-and-effect relationships -- correlation, plausibility, responsiveness, and temporality -- do not by themselves provide sufficient evidence. However, studies that provide information on
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Key Terms

  • biologic markers
  • stress factors
  • air pollutants
  • changes caused
  • forest stands

  • individual trees
  • ionizing radiation
  • pollutant concentrations
  • specific causes
  • chemicals herbicides

  • forested region
  • organic matter
  • potential usefulness
  • chemicals acid
  • sought criteria

  • regional pollution
  • single tree
  • observed pollutants
  • toxic elements
  • affects forests

  • mechanical disturbance
  • germ theory
  • forms parasitic
  • chronic stresses
  • strong correlation

  • sufficient evidence
  • causal agents
  • link causes
  • tree population
  • forest metabolism


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