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these areas very slowly because the substrate is low in <br /> nutrients and also is subject to wide fluctuations in <br /> moisture and temperature. Those plants which are adapted <br /> to conditions such as these are mostly weedy, and therefore <br /> the disturbed. sites either support a weed community or <br /> are essentially non-vegetated. Channelization has also <br /> produced gravel spoils along the stream which support <br /> similar communities . Recovery from disturbances is not <br /> uniform. The communities on more mesic sites recover more <br /> quickly than those on drier sites . <br /> Impacts on Vegetation <br /> The most obvious indications of impacts on vegetation are <br /> a change in its appearance or in its use by wildlife. Other <br /> . indications of adverse impacts are reductions in stability, <br /> diversity or productivity. The severity of an impact is <br /> closely related to the time it takes the vegetation on a <br /> site to recover. Destruction of a forest which may take <br /> 200 years to re-establish is more of an impact than destruction <br /> of a prairie which may require only 40 years for recovery. <br /> The rationale is that an impact is more severe if it upsets <br /> stability, diversity and productivity for a longer period of <br /> • time. <br /> Surface mining will destroy the vegetation on all of the site <br /> to be mined. This is a severe impact which is irreversible <br /> F-17 _ <br />