ARAVAIPA CREEK – BLACK FARM RIPARIAN REPORT by Mark D

ARAVAIPA CREEK – BLACK FARM RIPARIAN REPORT By Mark D. Dixon, Ph.D. April 13, 2021 Introduction This report examines the current condition of the Black Farm property on Aravaipa Creek and its potential to provide riparian habitat for the Southwestern Willow Flycatcher (Empidonax traillii extimus), Western Yellow-billed Cuckoo (Coccyzus americanus), and other riparian bird species under predicted conditions with full administration of SRP’s water rights (Ford et al. 2021). Current Riparian Vegetation at Black Farm I visited Black Farm on the morning of Oct. 9, 2020. Vegetation in the lower floodplain and channel (RS, “Riparian Shrub” area on Figure 1) was dominated by singlewhorl burrobrush (Hymenoclea monogyra), with scattered shrub-sized mesquite (Prosopis velutina), seep-willow (Baccharis salicifolia) shrubs near the channel, and a few blue palo verde (Parkinsonia florida). Burrobrush represented perhaps 95% of the woody plants immediately in and around the channel (see Figures 2, 3, and 5). Burrobrush is considered a xeroriparian pioneer shrub species, meaning that it is tolerant of frequent disturbance (e.g., floods) as well as dry conditions (Stromberg et al. 2006a). Seep-willow is a shallow-rooted riparian species that can occur across a range of hydrologic conditions but was most common along the upper San Pedro River on sites where groundwater levels were within 2.1 m (7 ft) of the ground surface. It is also thought to be an unpalatable species that may increase in riparian sites subject to browsing by livestock (Stromberg et al. 2006a). Other hydromesic species, including obligate phreatophytic (groundwater-dependent) trees and shrubs like Fremont cottonwood (Populus fremontii), Goodding’s willow (Salix gooddingii), and sandbar willow (Salix exigua), were not observed on the property. A woodland (bosque) dominated by velvet mesquite – estimated by the preserve manager to be 30-40 years old – with a few scattered tamarisk (Tamarix ramosissima) occurs on a higher surface to the south of the channel (VM, “Velvet Mesquite Community” on Figure 1, see also Figure 4). The former agricultural lands at Black Farm have been planted to native grasses (AF, “Agricultural Fields” on Figure 1). Current and Historical Vegetation Downstream of Black Farm Although no cottonwoods (or willows) were observed on the Black Farm property, several occur nearby. A few medium-sized cottonwood trees occur downstream from the property, just upstream of the Arizona Highway 77 bridge (Figure 6) and several mature trees occur at the base of the terrace on the north side of Aravaipa Creek, across the floodplain from the Black Farm property (Figure 3). An historical ground photograph from January 8, 1941 of Aravaipa Creek looking upstream from the Highway 77 bridge (Webb et al. 2007) shows a large open, cobbly channel, with a few large cottonwoods, mesquite, and catclaw acacia on the north bank

1 of the creek (Figure 7A). By October 23, 2002, the channel had narrowed, and woody vegetation had greatly increased, with burrobrush, seep-willow, and a few young cottonwood and sycamore (Platanus wrightii) trees evident on the south side of the channel (Figure 7B). In the figure caption for the 2002 photograph the authors further note that “Young black willow trees became established here but have died recently, possibly as a result of ongoing drought” and also mention the presence of the non-native species, tamarisk and tree-of-heaven (Ailanthus altissima), on the reach (Webb et al. 2007: p. 253). Some of the cottonwoods shown on the two historical photos may be the same as those that could be seen in 2020 on the north side of the floodplain and near the Highway 77 bridge. In the text (Webb et al. 2007: p. 248), the authors refer to this as a reach with intermittent flow and suggest that the presence of young native riparian trees was linked to opportunities for establishment provided by the effects of the 1983 and 1993 floods, but that the subsequent death of young willows suggests limitations on the availability of shallow groundwater to sustain obligate phreatophytes. Potential Effects of Hydrologic Enhancement Projections from a hydrologic model of Aravaipa Creek suggest that groundwater levels could be greatly enhanced under full administration of SRP’s water rights at Black Farm (Ford et al. 2021). Without enhancement, groundwater levels have fluctuated between approximately 9 ft (2.7 m) and 26 ft (8 m) below the channel bottom over the last ten years. With full administration of the water right, the model projects that groundwater levels at Observation Well #2 (see in Ford et al. 2021) would routinely intercept or exceed the elevation of the creek bottom within 4-5 years, suggesting both shallow groundwater levels and more frequent streamflow in the channel. Increases in groundwater elevation and in the frequency of surface flow could shift the conditions at Black Farm from those supporting xeroriparian desert wash vegetation to one with higher-frequency intermittent to perennial flow and shallow groundwater levels capable of supporting hydric, groundwater-dependent woody plants such as cottonwood and willow. The observations by Webb and others (2007) suggest that large floods (e.g., 1983, 1993) periodically provide the conditions necessary for recruitment of young cottonwood and willow trees (bare, moist alluvial sediments), with low groundwater levels currently being the limiting factor for their survival. With sufficient enhancement of groundwater levels, this limitation could be removed. Based on previous work on the upper San Pedro River (Stromberg et al. 2006a,b; Brand et al. 2011), on average, sites with surface streamflow frequency of >60%, maximum dry season depth to groundwater of <3.5 m (11.5 ft) in the floodplain, and annual fluctuation in groundwater levels <1 m (3 ft) were able to sustain existing cottonwood-willow forests, although tamarisk was often abundant on the drier sites (Figure 8 middle). Particularly high- quality riparian habitat, with greater cottonwood-willow dominance, occurred where flows were nearly perennial (>95% of the year), maximum groundwater depths were shallower (<2.5 m or 8 ft), and groundwater levels were more stable (<0.5 m or 1.6 ft annual fluctuation) (Figure 8 top). In contrast, sites with lower frequency flows (<60%), greater maximum depths

2 to groundwater (>3.5 m or 11.5 ft), and greater variability in groundwater levels (>1 m or 3 ft annual fluctuation) typically did not support healthy riparian forests dominated by cottonwood and willow (Figure 8 bottom, Stromberg et al. 2006a,b, Brand et al. 2011). SRP’s Adobe Preserve, about ¾ of a mile downstream of the Aravaipa Creek - San Pedro River confluence, contains a vibrant riparian ecosystem with mature Fremont cottonwoods and Goodding’s willows, as well as other vegetation types (SRP 2019b,c, Figure 9). This riparian ecosystem is supported in part by subflow from the Aravaipa Creek basin (SRP 2019b), suggesting that such subflow – particularly if enhanced by administration of SRP’s water right – might help support healthy riparian vegetation on lower Aravaipa Creek as well, if depth to groundwater is shallow enough. Healthy riparian ecosystems and diverse bird communities also exist farther upstream of Black Farm in Aravaipa Canyon (Figures 10 and 11), where shallow groundwater sustains perennial streamflow and lush cottonwood-willow forests. Bird Habitat Improvements in riparian vegetation condition, including the establishment and survival of cottonwoods and willows, could increase habitat suitability for many riparian bird species, particularly those that nest in higher canopy levels or dense mid-story vegetation and those dependent on surface water or moist soil conditions (see Figure 12, Brand et al. 2008, 2009, 2010, 2011). These include two species that are federally listed in Arizona, the endangered Southwestern Willow Flycatcher and the threatened western distinct population segment of the Yellow-billed Cuckoo. If combined with restoration of more hydric riparian vegetation in the channel and floodplain, the mesquite bosque on the terrace at Black Farm could provide secondary foraging habitat for flycatchers, cuckoos, and other species during breeding or migratory seasons (SRP 2019c). Individual species and overall bird diversity may also benefit from a complementary mix of cottonwood-willow, mesquite, xeroriparian shrubland, and restored grassland in close proximity (Brand et al. 2009). Gray Hawk (Buteo plagiatus), a species of concern in Arizona, nests in cottonwood trees, but uses a mix of surrounding habitat (e.g., mesquite, grassland) for foraging (Brand et al. 2009). In addition, hydrologic restoration at Black Farm could also provide habitat benefits downstream by supporting baseflows at Adobe Preserve and elsewhere on the lower San Pedro River (SRP 2019b). Nearly the entire San Pedro River corridor (Units 14, 15) and Aravaipa Creek (Unit 25) have been proposed as critical habitat for the Western Yellow-billed Cuckoo (hereafter cuckoo, USFWS 2020), with the San Pedro possibly sustaining one of the largest remaining populations (Brand et al. 2009). Characteristic breeding habitat for cuckoos includes large patches of riparian habitat dominated by cottonwood and willow (Salix spp.) trees along low gradient streams and rivers (USFWS 2020). Wohner and others (2021a,b), studying cuckoos along the Kern River in California, suggest that cuckoos require large tracts of riparian forest, but within these tracts preferentially select nesting sites within smaller, earlier successional trees – particularly willow – and dense foliage at multiple canopy levels. Stanek and others (2021) found generally similar nesting habitat requirements along the lower Colorado River. These

3 studies suggest that without periodic disturbance (or habitat management and restoration) that initiates new establishment of willows or other early successional tree species, habitat quality may decline with riparian forest maturation. In Arizona and elsewhere in the arid southwestern US, however, cuckoos may also use narrower and patchier areas with a mix of riparian and adjacent non-riparian habitats, including mesquite bosques, tamarisk, xeroriparian scrub along intermittent and ephemeral drainages, and oak woodlands, particularly in regions that receive mid-summer precipitation and humidity from the North American monsoon (USFWS 2020). These summer rains may support cuckoo nesting into September in southeastern Arizona by supporting high abundances of preferred cuckoo prey (large insects, small vertebrates including frogs and lizards). Cuckoos occur close to Black Farm on sites owned by SRP along the lower San Pedro River, including the Adobe, Stillinger, San Pedro River, Spirit Hollow, and Spirit Hollow Annex preserves (SRP 2019d). For the flycatcher, designated critical habitat on the San Pedro occurs only downstream of Benson (lower 78.4 miles of river) and does currently not include Aravaipa Creek except at its confluence with the San Pedro (USFWS 2013, https://ecos.fws.gov/ecp/species/6749#crithab). During the 1990s-early 2000s, the largest population of flycatchers in Arizona occurred along the lower San Pedro and adjacent middle Gila River (Paradzick and Woodward 2003). Katz and others (2009: p. 364 ) suggested that this area had “probably been a stronghold for this subspecies for decades,” noting that the southwestern subspecies had originally been described taxonomically from a specimen collected in 1940 near the current Adobe and Cook’s Lake preserves at the former townsite of Feldman. At the landscape scale along the San Pedro and the nearby middle Gila, flycatchers select dense vegetation within broad river floodplain reaches (Katz et al. 2009, Hatten and Paradzick 2003). At the patch (site) scale, flycatchers prefer areas with dense thickets of young willow (i.e., <10 years old) or tamarisk saplings (5-15 cm or 2-6 inch stem diameter) with a dense, even canopy, adjacent to moist soil or surface water. Within these patches, nest sites occur where foliage and stem densities are high. Suitable habitat structure may develop and be colonized by flycatchers within three years after willow germination (Katz et al. 2009), particularly if the site is within 30-40 km (19-25 miles) (Paxton et al. 2007) . Under some situations, birds have also used tamarisk patches on higher terraces supported by irrigation runoff, particularly when nearby natural habitats had been scoured by recent floods (e.g., in 1993) (Katz et al. 2009). Periodic natural flood disturbance, shallow groundwater, and high flow frequencies (e.g., perennial and interrupted perennial flows) have historically supported conditions for flycatcher habitat along portions of the lower San Pedro River (Katz et al. 2009), including the five SRP preserves on the lower San Pedro. Numbers on the preserves have dwindled, however, over the last decade with structural changes in the habitat due to maturation of the vegetation and other factors (SRP 2019d). Hence, creation of suitable habitat for flycatchers at Black Farm could be of major benefit to conservation of the subspecies in the area and could provide a buffer against declining habitat suitability due to vegetation maturation or sudden habitat losses in years with large floods or fires on the lower San Pedro River.

References Cited Brand, L.A., G.C. White, and B.R. Noon. 2008. Factors influencing species richness and community composition of breeding birds in a desert riparian corridor. Condor 110(2):199-210. Brand, L.A., D.J. Cerasale, T.D. Rich, and D.J. Krueper. 2009. Breeding and migratory birds: pattern and process. Chapter 8, In: Stromberg, J.C. and B. Tellman (eds.), Ecology and Conservation of the San Pedro River. University of Arizona Press, Tucson, AZ. Brand, L.A., J.C. Stromberg, and B.R. Noon. 2010. Avian density and nest survival on the San Pedro River: importance of vegetation type and hydrologic regime. Journal of Wildlife Management 74(4):739-754. Brand, L.A., J.C. Stromberg, D.C. Goodrich, M.D. Dixon, K. Lansey, D. Kang, D.S. Brookshire, and D.J. Cerasale. 2011. Projecting avian response to linked changes in groundwater and riparian floodplain vegetation along a dryland river: a scenario analysis. Ecohydrology 4(1):.130-142. Ford, J., G. Ten Eyck, and D. Gates. 2021. Expected Future Surface Flows and Depths to Groundwater at SRP’s Black Farm Preserve on Aravaipa Creek. Unpublished report prepared for Salt River Project by LRE Water. Hatten, J.R. and C.E. Paradzick. 2003. A multiscaled model of southwestern willow flycatcher breeding habitat. Journal of Wildlife Management 67:774–788. Katz, G., J.A. Haney, C.E. Paradzick, and D.B. Harris. 2009. Mitigation, restoration, and endangered species: hydrologic restoration on the lower San Pedro River. Chapter 19, In: Stromberg, J.C. and B. Tellman (eds.), Ecology and Conservation of the San Pedro River. University of Arizona Press, Tucson, AZ. Paradzick, C.E and A.A. Woodward. 2003. Distribution, abundance, and habitat characteristics of southwestern willow flycatchers (Empidonax traillii extimus) in Arizona, 1993-2000. Studies in Avian Biology 26:22-29. Paxton, E.H., M.K. Sogge, S.L. Durst, T.C. Theimer, and J.R. Hatten. 2007. The Ecology of the Southwestern Willow Flycatcher in Central Arizona—A 10-year Synthesis Report. U.S. Geological Survey Open-File Report 2007-1381. Salt River Project [SRP]. 2019a. Management Plan for The Black Farm Preserve, October 2004, Reviewed and Updated May 2019. Salt River Project, Environmental Services Department, Phoenix, AZ. Salt River Project [SRP]. 2019b. Adobe Preserve Baseline Inventory, September 27, 2003, Reviewed and Updated May 2019. Compiled by Salt River Project, Siting and Studies Division, Environmental Services Department, Phoenix, AZ.

Salt River Project [SRP]. 2019c. Management Plan for The Adobe Preserve, September 2003, Reviewed and Updated May 2019. Salt River Project, Siting and Studies Division, Environmental Services Department, Phoenix, AZ. Salt River Project [SRP]. 2019d. Roosevelt Habitat Conservation Plan Annual Report 2019 (Public version). Prepared for US Fish and Wildlife Service by Salt River Project, Environmental Compliance & Permitting, Biological & Cultural Services, Phoenix, AZ. Stanek, J.E., S.E. McNeil, D. Tracy, J.R. Stanek, J.A. Manning, and M.D. Halterman. 2021. Western Yellow‐Billed Cuckoo nest‐site selection and success in restored and natural riparian forests. Journal of Wildlife Management 1-12; 2021; DOI: 10.1002/jwmg.22020 Stromberg, J.C., S.J. Lite, M. Dixon, T. Rychener, and E. Makings. 2006a. Chapter C. Relations between streamflow regime and riparian vegetation composition, structure, and diversity within the San Pedro Riparian National Conservation Area, Arizona. In: Leenhouts JM, Stromberg JC, Scott RL (eds.), Hydrologic Requirements of and Consumptive Ground-water Use by Riparian Vegetation along the San Pedro River, Arizona: U.S. Geological Survey Scientific Investigations Report 2005–5163, 154 p. Stromberg, J.C., S.J. Lite, T.J. Rychener, L.R. Levick, M.D. Dixon, and J.M. Watts. 2006b. Status of the riparian ecosystem in the upper San Pedro River, Arizona: application of an assessment model. Environmental Monitoring and Assessment 115:145–173. U.S. Fish and Wildlife Service [USFWS]. 2013. Designation of critical habitat for Southwestern willow flycatcher—Final rule: Federal Register 78(2):344–534. [Also available at http://www.regulations.gov, Docket No. FWS–R2–ES–2011–0053.] U.S. Fish and Wildlife Service [USFWS]. 2020. Revised designation of critical habitat for the western distinct population segment of the yellow-billed cuckoo; proposed rule. Federal Register 85(39):11458-11594. Webb, R.H., S.A. Leake, and R.M. Turner. 2007. Chapter 20: Aravaipa Creek and other tributaries of the San Pedro River. In: The Ribbon of Green: Change in Riparian Vegetation in the Southwestern United States. University of Arizona Press. Wohner, P.J., S.A. Laymon, J.E. Stanek, S.L. King, and R.J. Cooper. 2021. Early successional riparian vegetation is important for Western Yellow‐billed Cuckoo nesting habitat. Restoration Ecology, p.e13376. Wohner, P.J., S.A. Laymon, J.E. Stanek, S.L. King, and R.J. Cooper. 2021. Challenging our understanding of western Yellow‐billed Cuckoo habitat needs and accepted management practices. Restoration Ecology, p.e13331.

Figure 1. Map of habitats at Black Farm (from Management Plan for The Black Farm Preserve, Oct. 2004, revised May 2019 (SRP 2019a). Modified to show approximate locations of photo points 1 (pp1) and 2 (pp2) on northeastern portion of property.

Figure 2. Photograph of photo point 1 location from June 17, 2004 on the northwest part of the preserve, looking north across the channel. Note dominance of burrobrush (Hymenoclea) in the lower floodplain and channel and presence of mesquite in the right foreground at the top of the bank. Photograph by Ruth Valencia.

Figure 3. View looking north across the channel, from photo point 1 on Oct. 11, 2017 (top, by Heather English) and Sept. 17, 2019 (bottom, by Ron Waline). Xeroriparian vegetation, primarily burrobrush, dominates the lower floodplain. Several large cottonwoods can be seen on the far north bank, across from Black Farm, to the upper left portion of the photographs. In the bottom photograph, water is flowing in the channel after recent rains upstream.

Figure 4. Views of mesquite to northwest (top) and southwest (bottom) of irrigation ditch at photo point 2 (Sept. 17, 2019). Note the mesquite bosque in the background. Photographs by Ron Waline.

Figure 5. Views of the channel and floodplain of Aravaipa Creek from the Black Farm property, looking upstream (top) and downstream (bottom). Some mesquite can be seen on the upper floodplain surface, whereas the lower surface is dominated by burrobrush. Photographs from Oct. 15, 2018 by the Black Farm Preserve manager.

Figure 6. Views of the channel and floodplain of Aravaipa Creek, looking upstream from the Arizona Highway 77 bridge, depicting Fremont cottonwood trees. Photographs by Mark Dixon (Oct. 9, 2020).

Figure 7. Historical repeat photography of Aravaipa Creek, looking upstream from the Arizona Highway 77 bridge (from Webb et al. 2007: Figure 20.11, p. 253). Top image (A) is from January 8, 1941. Bottom image (B) is from October 23, 2002. Note the large cottonwood tree to the left in image A and the young cottonwoods (right) and seep-willow (foreground) on image B.

Figure 8. Examples of riparian condition classes along the upper San Pedro River: top is class 3 (wet), middle is class 2 (intermediate), and bottom is class 1 (dry) (from Stromberg et al. 2006b: Figure 6).

Figure 9. Riparian vegetation at the Salt River Project’s Adobe Preserve. Photographs by Mark Dixon (Oct. 9, 2020).

Figure 10. Riparian vegetation and streamflow in Aravaipa Canyon, approximately 10 miles upstream from Black Farm. Photographs by Mark Dixon (Oct. 9, 2020).

Figure 11. Approximate locations of Aravaipa Canyon, Black Farm, and Adobe Preserve. Photo from Google Earth.

Figure 12. Schematic depicting habitat structure and riparian bird species characteristic of different vegetation types and foliage heights on perennial (top) and dry intermittent (bottom) stream reaches of the San Pedro River (e.g., Stromberg’s condition class 3 vs. 1, respectively, Stromberg et al. 2006a,b). Note the additional bird guilds and species supported on sites with perennial stream flow and a cottonwood-willow canopy and open water (top). Figure from Brand and others (2009: Figure 8.1, p. 159).