2014-05-15_REVISION - M1987064 - Laserfiche WebLink

Home Browse Search

1120 m c 0 .Q �U D_ ROOD, BRAATNE AND HUGHES Cool Temperature tonwood growth has led to field trials to improve water condi- tions for cottonwood conservation, the retention of remaining woodlands, and the restoration and reestablishment of wood- lands in degraded riparian zones (Johnson et al. 1995, Poff et al. 1997, Briggs and Cornelius 1998, Mahoney and Rood 1998, Springer et al. 1999, Bovee and Scott 2002). Water management strategies involving flow regulation downstream of dams can be of widespread benefit for riparian cottonwoods (Stanford et al. 1996, Poff et al. 1997, Mahoney and Rood 1998, Rood et al. 1998, Richter and Richter 2000, Hughes and Rood 2001, Stromberg 2001). Localized benefits can also be derived from supplemental water through irriga- tion or other treatments (Friedman et al. 1995, Molles et al. 1998, Sprenger et al. 2002). Knowledge of cottonwood water relations is also relevant to applications intended to restrict cottonwood expansion, which can also follow river regulation (Johnson 1997, 2000), or to influence competition between cottonwoods and other plants, particularly invasive weeds (Shafroth et al. 1994, Stromberg 1997, Gladwin and Roelle 1998, Sher et al. 2002). Several recent studies have demonstrated historic correla- tions between cottonwood status and stream flow. Pulses of cottonwood reproduction have accompanied years with high flow or appropriate flow patterns (Scott et al. 1996, 1997, Mahoney and Rood 1998, Rood et al. 1999). The next step in cottonwood restoration is just commencing with the alteration of river regulation patterns. Hughes and Rood (2003) recently reviewed strategies for the restoration of floodplain wood- lands, including two recent case studies documenting favor- able cottonwood responses to deliberate changes in stream flow regulation. In one case study, chronic dewatering of the lower St. Mary River in southern Alberta during the irrigation season led to the loss of more than 90% of the riparian black and narrowleaf Warm Figure 3. Generalized adaptive ranges of riparian cottonwoods of North America with respect to temperature and precipitation. Populus balsamifera, P. trichocarpa and P. angustifolia are in Populus section Tacamahaca, whereas P. deltoides and P. fremontii are in section Aigeiros along with the European species P. nigra, which may have an adaptive range generally simi- lar to that of P. deltoides. cottonwoods (P. trichocarpa and P. angustifolia) over the half - century following the 1951 completion of the St. Mary Dam (Rood and Mahoney 1995). Although flooding persisted downstream from that dam, flood flows were followed by abrupt flow decline that prevented successful cottonwood re- cruitment. In 1995, a natural flood flow occurred and the St. Mary Dam was managed to provide a relatively natural stage recession rate of 4 cm day -' (Rood and Mahoney 2000). Sub- stantial cottonwood seedling establishment resulted, in con- trast to the lack of recruitment following the previous flood years of 1964 and 1975. The lower Truckee River in the high desert of western Ne- vada provides an even more dramatic case study (Rood et al. 2003). This river was progressively dammed and dewatered, leading to the collapse of the aquatic and riparian ecosystems. Increased instream flows commenced in the early 1980s as part of a program to restore an endangered endemic fish, the cui -ui sucker (Chasmistes cujus). The collateral recruitment of Fremont cottonwoods (P. fremontii) as well as sandbar and other willows followed during 2 years in which the river stage gradually receded at about 2.5 cm day -1 following the period of seed release. The new cottonwoods continue to grow and are reestablishing habitat for birds and other wildlife that had been lost over the twentieth century. Conclusion Throughout the 1980s, several studies revealed the collapse of riparian cottonwood forests downstream from dams in western North America (Rood and Mahoney 1990). Investigations throughout the 1990s have partially clarified the ecophysio- logical dependency of riparian cottonwoods on stream flow and revealed aspects of the morphological and physiological adaptation of cottonwoods and willows to riparian floodplains. TREE PHYSIOLOGY VOLUME 23, 2003 0 A