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occur with removal of the hemic and fibric peat layers. These <br />factors are most important in their effect on plant soil and <br />water relations, and storage of peak flows. <br />The resulting bulk density may be found to be the most <br />important factor in the success of revegetation efforts. In most <br />plant species, the permanent wilting percentage (PWP) is taken to <br />occur at -15 bars. From Figure 3 and Figure 4, it can be seen <br />that if the remaining sapric material has a bulk density of 0.2 <br />g /cm3 or greater, then plants with a PWP of -15 will begin to <br />experience drought conditions at a moisture content of 20 to 25 <br />percent (by volume). (Bulk density of the surface layers would <br />always be expected to increase after excavation.) Wetland <br />plants, because of the positive water relations of their <br />environments, may have higher PWP's than average, and would thus <br />require greater moisture content to avoid drought conditions. <br />This may have serious implications for the viability of <br />revegetation efforts, particularly if conversion to dryland is <br />the objective. <br />Because the fibric peat layer is where essentially all of <br />the active storage takes place, the removal of this layer <br />eliminates the peat's ability to store and moderate peak flows. <br />As a result, surface flow tends to channelize and erode down to <br />the base material. This was the case at the Universal site No. 1 <br />where spring snow melt eroded gullies two feet deep through a <br />partial excavation at the valley bottom. The same effect was <br />noted, although to a lesser degree, at the Sacramento site. <br />• 39 <br />