The Irrigation Effect: How River Regulation Can Promote Some Riparian Vegetation
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River regulation impacts riparian ecosystems by altering the hydrogeomorphic conditions that support streamside vegetation. Obligate riparian plants are often negatively impacted since they are ecological specialists with particular instream flow requirements. Conversely, facultative riparian plants are generalists and may be less vulnerable to river regulation, and could benefit from augmented flows that reduce drought stress during hot and dry periods. To consider this ‘irrigation effect’ we studied the facultative shrub, netleaf hackberry (Celtis reticulata), the predominant riparian plant along the Hells Canyon corridor of the Snake River, Idaho, USA, where dams produce hydropeaking, diurnal flow variation. Inventories of 235 cross-sectional transects revealed that hackberry was uncommon upstream from the reservoirs, sparse along the reservoir with seasonal draw-down and common along two reservoirs with stabilized water levels. Along the Snake River downstream, hackberry occurred in fairly continuous, dense bands along the high water line. In contrast, hackberry was sparsely scattered along the free-flowing Salmon River, where sandbar willow (Salix exigua), an obligate riparian shrub, was abundant. Below the confluence of the Snake and Salmon rivers, the abundance and distribution of hackberry were intermediate between the two upstream reaches. Thus, river regulation apparently benefited hackberry along the Snake River through Hells Canyon, probably due to diurnal pulsing that wets the riparian margin. We predict similar benefits for some other facultative riparian plants along other regulated rivers with hydropeaking during warm and dry intervals. To analyze the ecological impacts of hydropeaking we recommend assessing daily maxima, as well as daily mean river flows.
KeywordsCeltis reticulata Hells canyon Hydropeaking Salmon river Snake river
This research was supported with funding from Idaho Power Company (IPC), the Natural Sciences and Engineering Research Council of Canada, Alberta Innovates, and Alberta Environment and Parks. We extend thanks to Robert Simons of Simons and Associates of Colorado, and Gary Holmstead, Toni Holthuijzen, Frank Edelman, and Allen Ansell of IPC for their insightful discussions, Karen Zanewich for assistance with data analyses and graphics and two anonymous reviewers for their very helpful advisements.
Compliance with Ethical Standards
Conflict of Interest
The authors declare that athey have no conflict of interest.
- Asherin DA, Claar JJ (1976) Inventory of riparian habitats and associated wildlife along the Columbia and Snake rivers. Vol 3A. College of Forestry, Wildlife, and RangeSciences, University of Idaho, MoscowGoogle Scholar
- Bejarano MD, Jansson R, Nilsson C (2017) The effects of hydropeaking on riverine plants: a review. Biol Rev https://doi.org/10.1111/brv.12362
- Coggins VL, Cassirer EF, Matthews P, Hansen M (2000) Rocky Mountain bighorn sheep transplants in Hells Canyon. Proc North Wild Sheep Goat Counc 12:68–74Google Scholar
- Daubenmire R (1959) A canopy-coverage method of vegetational analysis. Northwest Sci 33:43–64Google Scholar
- DeBolt AM, McCune B (1995) Ecology of Celtis reticulata in Idaho. Gt Basin Nat 55:237–248Google Scholar
- Dixon MD, Johnson WC (1999) Riparian vegetation along the middle Snake River, Idaho: zonation, geographical trends, and historical changes. Gt Basin Nat 59:18–34Google Scholar
- Doody TM, Benger SN, Pritchard JL, Overton IC (2014) Ecological response of Eucalyptus camaldulensis (river red gum) to extended drought and flooding along the River Murray, South Australia (1997–2011) and implications for environmental flow management. Mar Freshw Res 65:1082–1093CrossRefGoogle Scholar
- Edenhofer O, Pichs-Madruga R, Sokona Y, Seyboth K, Matschoss P,Kadner S, Zwickel T, Eickemeier P, Hansen G, Schlömer S, von Stechow C (2011) IPCC special report on renewable energy sources and climate change mitigation. Prepared by Working Group III of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, UKGoogle Scholar
- Huschle G (1975) Analysis of the vegetation along the middle and lower Snake River. Msc Thesis, University of IdahoGoogle Scholar
- Johnson CG, Simon SA (1987) Plant associations of the Wallowa-Snake Province, Wallowa-Whitman National Forest. USDA Pacific Northwest Region Publications R6-ECOL-TP-255B- 86, Portland, ORGoogle Scholar
- Jones Jr JB (2016) Hydroponics: a practical guide for the soilless grower. CRC Press, Boca Raton, FLGoogle Scholar
- McCune B, Mefford MJ (2009) HyperNiche, Version 2.0. MjM Software, Gleneden Beach, OR, USAGoogle Scholar
- Mortenson SG, Weisberg PJ (2010) Does river regulation increase the dominance of invasive woody species in riparian landscapes? Glob Ecol Biogeogr 19:562–574Google Scholar
- Naiman RJ, Décamps H, McClain ME (2005) Riparia: Ecology, Conservation and Management of Streamside Communities. Elsevier Academic Press, AmsterdamGoogle Scholar
- Rood SB, Braatne JH, Goater LA (2010b) Responses of obligate and facultative riparian shrubs following river damming. River Res Appl 26:102–117Google Scholar
- Salzer MA, McCord VAS, Stevens LE, Webb RH (1996) The dendrochronology of Celtis reticulata in the Grand Canyon: assessing the impact of regulated river flow on tree growth. In: Dean JS, Meko DM, Swetnam TW (eds) Tree rings, environment and humanity: Proceedings of the International Conference. Radiocarbon, Department of Geosciences, University of Arizona, Tucson, pp 273–281Google Scholar