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<br />002722 <br /> <br />Opportunities for Ecological Improvement Along the Lower Colorado River <br />Mark Briggs and Steve Cornelius <br />7/24/97 <br /> <br />the eight plots were seeded with quailbush while the remaining four plots were seeded <br />with equal amounts of screwbean mesquite, honey mesquite, and palo verde. Two of <br />the quailbush plots and two of the mesquite and palo verde plots were fertilized. The <br />plots were flood irrigated three times in 1986 with two to five centimeters of water and <br />once in 1987 with ten to 15 centimeters of water (Pinkney 1992). <br />Results: Germination rates for all plants was initially high. In 1988, quailbush seedlings <br />were well established (more than 1,000 seedlings germinated), and approximately 1,900 <br />screwbean mesquite, 600 honey mesquite, and 25 palo verde seedlings had also <br />established. However, mortality was high in the following years. All palo verde <br />subsequently died as well as many of the mesquite seedlings. Rabbit damage also <br />occurred and seemed to affect the survival and growth of honey mesquite more than <br />screwbean (Pinkney 1992). Only three to ten mesquite seedlings were found in 1997 in <br />each of the four plots and all were protected with chicken wire baskets. <br />Lessons Learned: Though difficult, it is possible to revegetate in areas characterized by <br />high soil salinity by using appropriate plant materials and innovative irrigation and <br />planting strategies. However, revegetating areas characterized by high soil salinity <br />should generally be avoided. Evaluating soil chemistry prior to planting allows <br />revegetation experts to place plant materials in areas where they are likely to survive, <br />improving the overall effectiveness of the revegetation effort (Anderson 1989). <br /> <br />Site #4 <br />Cibola National Wildlife Refuge Dredge Spoil Site <br />Location and Size: This site covers 28 hectares (70-acre) and is located about eight km <br />east of Palo Verde, California. It is divided by a levee that parallels the Colorado River. <br />Revegetation work began on the East Dredge Spoil area in 1977 and on the West <br />Dredge Spoil area in 1978. <br />Objective: To better understand the feasibility of using revegetation to improve the <br />condition of ecologically-damaged reaches of the Colorado River. This was the Bureau <br />of Reclamation" s first revegetation experiment <br />Completion Date: 1978 <br />Pre-Project Site Conditions: Russian thistle dominated the site prior to project initiation. <br />Soil survey data indicated that soils on the east side of the site are primarily sands with <br />a thin clay layer situated 1 m to 1.5 m (three to five ft) below the surface. In contrast, <br />soils on the west side of the site are primarily loam, but were covered by .5 m to 3 m of <br />dredge spoil material. Depth to the saturated zone of the soil profile varied from 3 m to <br />4.5 m (Pinkney 1992). <br />Project Strategy: In total, approximately 2,000 cottonwood, willow, honey mesquite, and <br />blue palo verde trees and shrubs were planted as two-foot-tall rooted cuttings. A <br />variety of planting techniques were used. Approximately 125 trees of all species were <br />planted in 20 cm diameter holes augered to a depth of 1.5 m. Numerous trees were <br />also planted in holes 30 cm in diameter and 3 m deep as well as holes 5 cm in diameter <br />and 3 m deep. A drip irrigation system was installed that delivered water at a rate of <br />four gallons per hour to each planted tree or shrub. Each tree was watered with 32 <br />gallons per day for at least 150 days. <br /> <br />Page 10 <br />