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<br />Biological issuesJ comment to SWSlt August 2004 <br /> <br />3 <br /> <br />\ <br />..1 <br /> <br />Theme: Cottonwood Crisis, Changing Channels? <br /> <br />In generaly it appears possible that the great pulse of increased woodland vegetation and <br />narrowing of the Plains river channels from the late 19th Century until about the 1960s has <br />ended, and is now changing again as cottonwoods and some willows fail to regenerate and <br />degrade, invasives and shade-tolerant species occupy the riparian understory, and sedimentary <br />and fluvial processes change in response to land use and changes in flow regimes after decades <br />of imposed stability. The evidence on cottonwoods in crisis is partial, but compels attention <br />(Bratton at at 1995, Friedman in Knopf and Samson 1997, Johnson 1994, Johnson 1997, Nadler <br />and Schmumm 1981) Snyder and Miller 1991)4 At about the same time that there was massive <br />conversion and drainage of wetlands of all sorts. there was also increase in woody habitats along <br />mainstems, and the establishment of the wetted areas irrigated. sub-irrigated, and supplied by <br />seepage and percolation from ditches and canals. Now~ that -new" riverine habitat is changingJ <br />but there is .no restoration of the long-gone wetlands areas. If current policy leads to dewatering <br />irrigated areas and the -inefficiencies. of agricultural water use are endedt what will be left? <br /> <br />~ <br /> <br />Wohl (2001t espec.. 101-105) points out that in 1883 the whole area from La Porte to the Platte <br />was then described as .one vast network of irrigating canals"; the Front Range hydrology had <br />become a .vast plumbing schemeR.. The flows needed for diversity were regulated away, (Richter <br />and Richter 2000, and the geomorphic changes have been complicated by the biological <br />responses (see also Tockner et at 2002)4 <br /> <br />As the policies for the Platte River endangered species, and urban supply needs are <br />implemented, one must wonder what kind of environment will remain, in biological as well as <br />social terms? The regional aggregation of impacts, such as .only 5% of water will be removed-, <br />is necessarily (given limits on analyses available and funded) uninformative, since the entire <br />problem sets of connectivity and thresholds are aggregated out of visibility (see Fausch at at <br />2002 for s.uperb explanation of this kind of problem). The right 5% might be almost meaningless, <br />while the wrong 5% could be very consequential- we would prefer to know more before we act. <br />And, the goal of moving some amount may require the act of moving considerably morey with <br />considerably larger potential surprise consequences.. If available partial substitutes for the <br />dramatically impaired original envjronments are now undergoing natural succession along the <br />mainstems, as cottonwoods age and are not reproduced, and the variety of unintended wetlands <br />supported by agricuttural -inefficiency- are lost, the idea of only small impacts becomes <br />increasingly unrealistic and the imperative to consider the .bigger picture becomes very strong.. <br /> <br />Theme: .nvesives <br /> <br />FinanYt a 'ast theme appeared in the survey: the lack of understanding of how to relate flow <br />regimes and management choices never before available to the need for invasive vegetation <br />management. There is a significant State commitment, for instancet on Tamarisk and Russian <br />Olive~ but the plan seems un-related to flow allocations or management choices. The literature is <br />sparse, and that surveyed contained only some mentions of drought impacts on Russian Oliv9t <br />drought tolerance of Tamarisk. and drought impacts on changing riparian vegetation in <br />combination with hydrograph changes. Similarly, invasive grass studies may not have <br />considered possible management manipulations related to water re-allocations (e.g. Christian <br />and Wilson 1999). See Amlin and Rood 2002, Katz and Shafroth 2003t Knopf and Samson 1997, <br />Nadler and Schumm 1981 f Snyder and Miller 1991. We might safva a major problem- or not! <br /> <br />SUMMARY: <br />We're on the verge of very serious changes on the Plains. without adequate knowledge of current <br />conditions -.how much of the wetted environment is agricultural in origin? What is going on with <br />mainstems right now and in the next five years? And, Uttle attention is being di.rectect to the <br />criticai -big picture- and the intermediate scale of research, where Fausch et al. point out things <br />actually live. SWSI, through its technical staff and the Roundtables, should consider asking the <br />Water Conservat;on Board to convene at teast further inquiry with CSU and agencies.. <br />