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<br />UJ~(:.:;a <br /> <br />Opportunities for Ecological Improvement Along the Lower Colorado River <br />Mark Briggs and Steve Cornelius <br />7/24/97 <br /> <br />season. In 1996 and 1997, the frequency with which the planted area was flood <br />irrigated was inqeased to bi-monthly. <br />Results:. All of the cottonwoods that were planted have survived to date (see cover <br />photograph). However, by 1997, about 90% of the willows have died. The high <br />mortality rate is believed to be due to localized soil salinity problems. <br />Lessons Learned: As revegetating with native riparian plants often requires significant <br />irrigation inputs (particularly during the first three summers), having control of the <br />land and the water rights that go with the land is often critical to success. Flood <br />irrigation may help to remove salts from soils to the point tolerated by at least some <br />native riparian plants. In addition, future revegetation efforts of this magnitude may <br />benefit if portions of the site are selectively harvested for plant materials. Such a <br />strategy would create a multiple-age stand of trees whose greater structural complexity <br />may benefit bird and other wildlife species (Steve Hill, pers. comm., 1997). <br /> <br />Site #8 <br />Mitlry Lake <br />Location and Size: The 23-hectares (57-acre) Mittry Lake revegetation site is located on <br />the Arizona side of the Colorado River roughly 15 miles north of Yuma. The Mitlry <br />Lake Wildlife area borders the revegetation site to the west and the Gila Gravity Main <br />Canal is immediately to the east <br />Objective: To enhance habitat for wildlife <br />Completion Date: April 1986 <br />P~e-Project Conditions: Vegetation found on site prior to project initiation consisted <br />mainly of sparse desertscrub on high elevated areas and mixed riparian vegetation <br />along several of the washes on the site's southern end. Soil types were found to be <br />highly variable, ranging from large rocks to silts and clays. Water table depths were <br />estimated at two to four meters (six to 14 feet) beneath soil surface (Pinkney 1992). <br />Project Strategy: Six revegetation zones were established on the lake site between March <br />and April 1986. Each of the zones was fenced and tree planting holes were augered to <br />saturated soil (2 m to 4 m deep) using an 38 cm (18-inch) diameter auger. Holes for <br />shrubs were augered 2 m deep using a 19 cm auger. Planting began in March 1986 and <br />was completed in April 1986. All trees and wolfberry shrubs were grown in one gallon <br />cans; quailbush plants were grown in small biodegradable containers. All trees and <br />shrubs were irrigated using a drip system and wire baskets were used to protect plants <br />from wildlife damage. Irrigation rates varied with revegetation zone, but all plants <br />generally received water each day for the first 30 days, at a rate of 18 gallons per day <br />for trees and 3 gallons per day for shrubs (Pinkney 1992). <br />Results: At the end of the 1988 growing season, only a few cottonwoods were taller <br />than four meters. Of the vegetation planted, willows appeared to have the slowest <br />growth rates, possibly due to water stress and damage from deer browsing. Estimates <br />of water table depths in 1988 indicated that depths were much greater than the two to <br />four meters initially estimated. The largest of the planted trees were those taking <br />advantage of water leaking from a canal just up hill from the revegetation site. <br /> <br />Page 13 <br />