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<br />63 <br /> <br />/ <br /> <br />Meehan et al. (1977) describe and illustrate a hypothetical e,xample of <br />the seral stages during the ecological succ,e,ssion of a small first. to <br />fourth order mountain stream in the Pacific northwest following a <br />catastrophic disturbance. It was assumed that the riparian community was <br />in a climatic climax or edaptic climax prior to a catastrophic dis,turbance <br />caused by clear cutting, fire, flooding, or damage caused by the s,couring <br />action of ice, sediment and organic debris. Channelization, clearing and <br />snagging operations, dredging and filling, channel realignment and, <br />overgrazing are additional examples of man-caused perturbations that <br />destroy the riparian zone. <br /> <br />Recovery of the riparian zone begins with vegetational growth and a <br />steady increase in biomass (Figure 7). As the height of the vegetation <br />increases, shading increases and water temperature and primary production <br />decrease. Water infiltration within the riparian zone increases with an <br />increase in leaf litter which reduces the alDount of direct runoff, sediment <br />and influx of inorganics. Deciduous shrubs and trees ,,,,ithin the riparian <br />zone contribute most of the litter during the early ye,ars of recovery. The <br />impacted area will move through a series of seral stag,es in which the <br />energy base of the stream community is initially domir.,ated by alga,e, later <br />dominated by deciduous detrital inputs and u,ltimately dominated by' <br />coniferous inputs. The later seral stages will tend t,o include a complex <br />mosaic of herbaceous ground cover, deciduous shrub lay,er and conif erous <br />overs tory. <br /> <br />DZrl~ <br />f). ~~ sr..",-- <br />Y.i SMlfUa <br />.. ...,,,.. ~YE~ <br />~J2~ <br />&tr <br /> <br />rsPI'.,._~D'" Ul 'h. ,i~r18n .01011 ttlrw.h <br />tt_. <br /> <br />(Modtfied from Thoau et al ) 'H9) <br />