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utf/U:1/LUI71 SUN UH:5L r~ne <br />.'i <br />®avid J. <br />Ecologist <br />May 14, 2001 <br />C~ <br />Cooper, Ph.D. <br />Lori Potter <br />Kelly~Haglund~Gamsey+Kahn LLC <br />1441 18th St., # 300 <br />Denver, CO 80202 <br />303.296.9412 <br />303.293.8705 fax <br />www.khgk.mm <br />IootterQkhclk.mm <br />Dear Ms. Potter, <br />i <br />Divid J. Caoper Phone 303 498 8441 <br />2fi90 La}ayalte Drive Fak 303 498 But <br />9oulder, LO 80905 rrmell: dcooper~Jrtni.net <br />Subject: Cottonwoods near the proposex! Platteville gravel pit <br />At your request, I am providing an analysis of the potential affects of the proposed Platteville <br />gravel piton plains mttonwood (Populus deltoides Marshall subsp. monilifera (Alton) <br />Eckenwalder). I will address two critical issues (1) potential affects of pit dewatertng on <br />mttonwoods, and (2) channel stabil'sty and diking. <br />Plains mttonwood is the only tree species present along most reaches of the South Platte <br />River in Colorado, and it provides a number of crttiral ecological functions. The tall, complex <br />canopy structure provides important habitat for migratory birds, including songbirds, bald <br />eagles, cavity nesting birds, and owls, among others. The continuous cottonwood canopy <br />provides an important mrrtdor for wildlife movement along the Front Range. The <br />cottonwood canopy also shades the river, maintaining cooler water temperatures, and <br />providing leaf litter input that drives the aquatic food chain, and supports the fish community. <br />Tree roots stabilize stream banks, preventing erosion. The anaerobic soils likely provide <br />important water quality functions, removing pollutants and nutrients. <br />Plains cottonwood is the North American tree speces most susceptible to drought induced <br />xylem cavitation (Tyree et al. 1994). Cavitation, and the diebad< of leaves, branches, stems, <br />and entire trees omurs when water tables drop below tree roots, or during extreme droughts <br />when entire river systems and their aquifers dry up. My own research (Cooper and D'Amico <br />1996, Cooper et al. ms.} and from researchers with the U.S. Geological Survey, Biological <br />Resources Division (Scott et al. 2000) indicates that water table declines of as little as 2-3 <br />feet below mttonwoods can lead to severe water stress. This stress can cause leaf, twig <br />and whole tree dieback, and stress begins within 2-3 weeks of drawdown, and if prolonged <br />for many months pn lead to tree death. Of course, the drawdown is critical during the <br />summer months when trees are actively growing and acquiring water from the aquifer. <br /> <br />This issue is critical because the "matamum theoretical water level dedines" figure provided <br />by Leonard Rice Consulting Water Engineers, Inc. in a letter report to Greg Rousch, dated <br />