Riparian habitats have been in decline throughout the southwestern U.S. since ca. 1900, as water management practices (i.e., river damming, channelization, and water diversion) have been implemented to facilitate flood control, livestock grazing, irrigation agriculture, and urbanization (Shafroth et al. 2005). Such water management has reduced the frequency and intensity of flooding events and thus the potential for establishment and regeneration of most native woody riparian species (Stromberg et al. 1991, Scott et al. 1997). As native willows (Salix spp.) and cottonwoods (Populus spp.) have declined, non-native tamarisk (Tamarix spp.) have invaded, resulting in a widespread shift from riparian habitats dominated by native tree species to those dominated by exotic species (Hunter et al. 1988, Shafroth et al. 2005). Riparian habitats support both highly diverse and unique assemblages of plant and animal species, particularly in desert landscapes (Naiman et al. 1993, Fleishman et al. 2003). In the southwestern U.S., where riparian habitat comprises less than 1% of the landscape, species richness of breeding birds is higher in riparian habitat than in all other terrestrial habitats combined (Knopf et al. 1988), and avian population sizes may be up to 10 times higher in riparian habitats than in surrounding upland habitats (Stevens et al. 1977). Because tamarisk stands support few bird species compared with native riparian forest (Hunter et al. 1988, Finch and Yong 2000), the widespread shift from native to non-native vegetation may dramatically reduce the suitability of tamarisk-dominated riparian areas as wildlife habitat. The introduction of tamarisk leaf beetles (Diorhabda spp.) into the Virgin River basin has caused a disruption in the nesting behavior and population distribution of multiple avian species, including the endangered Southwestern Willow Flycatcher (UDWR unpublished data). While flycatchers in the St George area prefer nesting in tamarisk trees and tamarisk dominated habitats, tamarisk leaf defoliation has occurred during peak breeding which has caused declines in reproductive success, in addition to habitat use shifts. Specific habitat restoration and habitat enhancement projects are thus needed to address the unique ecological and biological relationships between the tamarisk leaf beetle and flycatchers. This project also maintains previously funded WRI projects (819 Virgin River Riparian Restoration Project for Southwestern Willow Flycatcher and 2312 Virgin River Avian Habitat Enhancement), as well as numerous restoration projects conducted under the direction of UDWR from 2008-2018.

Our goal is to restore and enhance native riparian habitat along the Virgin River where current conditions will allow us to maximize the impact of proposed efforts. Our efforts will support the WRI focus of improving watershed health, biological diversity, water quality/yield, and sustainable use of natural resources. We propose to accomplish this by removing non-native plants such as tamarisk (Tamarix ramosissima), by replanting, in lowland areas, native plants such as willows (Salix exigua, S. gooddingii), cottonwood (Populus fremontii), and velvet ash (Fraxinus velutina), and maximizing water flow and storage in appropriate areas. Recent work suggests that, for many bird species, abundance is highest at intermediate levels (40-60 %) of tamarisk cover (van Riper et al. 2008). Because of the high proportion of tamarisk at many sites in Washington County, complete eradication of tamarisk may also reduce habitat quality for the Southwestern Willow Flycatcher. Thus, following recommendations by van Riper et al. (2008), we propose to remove 20-40 % of tamarisk at historic (>5 years) and potential breeding sites (i.e. not currently occupied by the flycatcher). At selected recently occupied (< 5 years) or currently occupied flycatcher breeding sites, we will adopt a conservative approach by removing <10 % of tamarisk (typically single trees or small patches of trees) or 10-20% of old growth, mature coyote willow trees. Due to variation in current conditions among sites and the presence of Southwestern Willow Flycatchers at some sites, objectives will vary and be site specific. Our primary objective is to maintain or enhance four currently occupied (2018) flycatcher breeding sites along the Virgin River in St George, Utah; restore three known historic (2010, 2013) breeding sites along the Virgin River; and create additional habitat at multiple locations that will be suitable for nesting flycatchers and reduce fragmentation of Virgin River riparian habitat.

The proposed actions focus on restoring, enhancing, and re-creating native riparian habitats. Risks of not performing the proposed actions include further deterioration of riparian and 100-year floodplain habitats or, at minimum, no net increase in suitable riparian habitat in Washington County. Because recovery of the endangered Southwestern Willow Flycatcher will depend on the restoration and maintenance of native riparian habitats, not pursuing the proposed project will further delay the species' recovery and, ultimately, it's delisting. Additional risks of not performing the proposed activities include the continued presence and spread of tamarisk, which increases potential flood damage and fire danger to communities along the Virgin River. Despite the benefits that the proposed activities would have for lowland riparian obligate animal species and lowland habitats in general, there are risks associated with the proposed activities, particularly with respect to currently available potential and suitable flycatcher habitat. Removal of non-native vegetation may temporarily eliminate potential flycatcher nesting sites, alter processes that influence habitat quality (e.g., food availability, microclimate conditions), and reduce habitat patch sizes and habitat connectivity. We propose to implement restoration activities in such a way as to minimize these risks. For example, we seek to remove only 20-40 % of tamarisk at unoccupied sites and 5-10 % of tamarisk at occupied sites. This approach should minimize any potential negative effects of restoration activities on flycatchers currently using the project area.

Restoration activities proposed here contribute directly or indirectly to objectives outlined by a number of management plans currently in place. At the federal level, our proposed activities address a number of recovery actions outlined in the Southwestern Willow Flycatcher recovery plan. By implementing our proposed activities, we will contribute to recovery actions 1.1.2.2, 1.1.2.3, 1.1.3.2, 1.2, 2.1.1, 2.1.2, 2.1.3, 2.1.4, 2.1.5, 2.1.6 (USFWS 2002). Our proposed activities are also consistent with habitat restoration and management activities that would be included under a Safe Harbor Agreement between private landowners in Washington County and the U.S. Fish and Wildlife Service (USFWS 2008). At the state level, our proposed activities address four specific conservation actions recommended by Utah's comprehensive wildlife conservation strategy (CWCS) for the Southwestern Willow Flycatcher, a Tier 1 species (Sutter et al. 2005). These actions include protecting suitable nesting sites, mitigating losses of suitable habitat, managing and restoring lowland riparian for suitable habitat, and implementing tamarisk control programs that do not negatively impact nesting flycatchers. By implementing these actions we will also generally enhance lowland riparian habitat, which the CWCS ranks as the highest priority habitat in need of conservation in Utah (Sutter et al. 2005). In Utah, lowland riparian habitat is the rarest habitat type and is under the greatest threat, yet is the second most important habitat in terms of vertebrate biodiversity and in its importance to Tier 1, 2, and 3 species. At the local level, our proposed actions fulfill a central objective of the Virgin River Resource Management and Recovery Program (VRRMRP) and the Virgin River Management Plan (VRMP), which is the enhancement and protection of riparian and 100-year flood plain habitats (UDNR 2002).

Tamarisk has been shown to increase fire frequency and intensity within riparian habitats (Busch and Smith 1995, Ellis 2001, Lite and Stromberg 2005). In addition to increase fire threats to native riparian habitat, tamarisk forests in Washington County produce a high fuel load within close proximity to multiple homes, business, and many other manufactured structures. Removing tamarisk via the proposed habitat restoration project would decrease the threat and magnitude of fires in such areas.

Water use from tamarisk communities and daily transpiration rates of tamarisk have been shown to be within the water use range of native riparian woody plants (Owens and Moore 2007). However, tamarisk can increase hydraulic roughness by altering alluvial deposits causing river channel narrowing (Manners et al. 2013). Riparian habitats and flycatcher breeding sites could greatly benefit from the proposed project by removing tamarisk and allowing an increase in the natural meandering flow of a stream located within a wide floodplain (e.g. Virgin River).

All restoration activities will be conducted between November and March, outside of the local growing season, and under the direction of a UDWR wildlife biologist. During tamarisk removal efforts, prior to initiating work, a UDWR biologist will survey each site and flag or paint individual non-native trees, or clumps of non-native trees, to be removed. A UDWR crew composed of one biologist and multiple technicians will cut tamarisk near the base of each trunk by hand and spray cut stem surfaces with a Garlon 4 herbicide mixture within three minutes of cutting. Cut material will be placed on site in slash piles to be burned. At sites dominated by mature willow, a UDWR biologist will survey the area and mark specific locations for willow cutting and removal. No herbicide will be applied. Areas cleared of tamarisk, as well as adjacent areas where tamarisk was absent, will be replanted with native plant stems. Coyote willow and Goodding's willow stems will be planted in a 3:1 ratio where elevation will allow willow survival and growth. Cottonwood stems will also be planted in low densities above bank-full elevation. Willow and cottonwood stems to be used for replanting will be harvested from City and private lands in November and December, following the onset of dormancy, by a UDWR crew composed of one biologist and multiple technicians. Stems will be cut in > 6-ft lengths, soaked in water, and planted within two weeks of cutting. In preparation for planting at sites accessible to heavy equipment, St. George City or the Washington County Water Conservancy District will be requested to auger 6-in diameter and 6-ft deep holes, located at 8-ft center intervals, using a hydraulic auger mounted on a back-hoe or skid-steer. Where conditions do not allow access to heavy equipment, or when heavy equipment and operator are unavailable, the UDWR crew will use standard hand-held post-hole diggers, or a portable Stihl BT 121 earth auger with a 6-in diameter bit to auger holes according to the specifications previously described. Personnel will plant stems up to 6-ft deep, in clusters of three stems per hole, using a water jet stinger to reach the desired depth and to maximize mud-to-stem contact while backfilling the hole with dirt. After backfilling holes, exposed stems will be cut 1 foot above the ground and the cut stem surface coated with latex paint, thereby preventing initial budding and promoting root production.

During performance of restoration activities, a UDWR wildlife biologist will describe the affected area (location, acres affected, pre-restoration condition), date(s) of restoration work, and a description of the work accomplished within the affected area. To document revegetation success qualitatively, the biologist will establish photo points immediately following completion of restoration activities. A marker will be established at each site, its location marked with GPS, and representative photos taken from the marker at three-month intervals. Lens magnification, direction (compass bearings) of lens, and camera height will be recorded on each interval and duplicated when taking follow-up photos. Restored areas will also be periodically observed by UDWR personnel during flycatcher monitoring throughout the summer months and during fish sampling between March and November.

UDWR will collaborate with the Washington County Flood Control Authority, American Conservation Experience (ACE), and the Lower Virgin River Fire Council, which members include: St. George City, Washington City, Santa Clara City, Washington County, Virgin River Program, BLM, Utah Division of Forestry & Fire, UDWR, and USFWS.