Western North American Naturalist Volume 72 Number 3 Article 6 11-5-2012 Inundation depth, duration, and temperature influence rF emon cottonwood (Populus fremontii) seedling growth and survival L. C. Auchincloss University of California, Davis, CA, [email protected] J. H. Richards University of California, Davis, CA, [email protected] C. A. Young Stockholm Environment Institute, Davis, CA, [email protected] M. K. Tansey Bureau of Reclamation, Sacramento, CA, [email protected] Follow this and additional works at: https://scholarsarchive.byu.edu/wnan Part of the Anatomy Commons, Botany Commons, Physiology Commons, and the Zoology Commons Recommended Citation Auchincloss, L. C.; Richards, J. H.; Young, C. A.; and Tansey, M. K. (2012) "Inundation depth, duration, and temperature influence rF emon cottonwood (Populus fremontii) seedling growth and survival," Western North American Naturalist: Vol. 72 : No. 3 , Article 6. Available at: https://scholarsarchive.byu.edu/wnan/vol72/iss3/6 This Article is brought to you for free and open access by the Western North American Naturalist Publications at BYU ScholarsArchive. It has been accepted for inclusion in Western North American Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. Western North American Naturalist 72(3), © 2012, pp. 323–333 INUNDATION DEPTH, DURATION, AND TEMPERATURE INFLUENCE FREMONT COTTONWOOD (POPULUS FREMONTII) SEEDLING GROWTH AND SURVIVAL L.C. Auchincloss1,4, J.H. Richards1, C.A. Young2, and M.K. Tansey3 ABSTRACT.—Fremont cottonwood (Populus fremontii) is an early successional foundation species found in riparian forest ecosystems in the North American Southwest. Along rivers, the upper limit of the seedling establishment zone depends on the proximity of seedling roots to the declining water table. The lower limit is a function of the maximum elevation of inundation or scour. Fremont cottonwood seedlings are likely to experience short-term (1- to 5-week) inun- dation during their first year of growth under both natural and human-influenced hydrologic regimes. Previous studies show that inundation can account for more than 70% of seedling mortality during this time. Using controlled inundation experiments, we found that seedlings of Fremont cottonwood have high tolerance of inundation to the soil surface and a reasonable tolerance of complete shoot submergence for a duration of 1 or 2 weeks (22% and 50% mortality, respec- tively). Mortality increased linearly with days of complete submergence (mortality percentage = 4.6 + [2.5 × days of submergence]). Warm water temperature (25/18 °C day/night) during complete submergence adversely affected seedling biomass and survival, resulting in 64% mortality versus 39% with cooler water temperatures (18/11 °C day/night). Our results indicate that establishment of new Fremont cottonwood populations in the riparian corridor will be more successful when flows do not completely cover the shoots of seedlings for more than 2 weeks and if water tempera- tures during inundation are cool. From the perspective of the management of river flows for cottonwood recruitment, deep, prolonged, late-season (warm water) inundations are the most detrimental. RESUMEN.—El álamo negro (Populus fremontii) es una especie de sucesión temprana en los ecosistemas de bosques ribereños, en el suroeste norteamericano. A lo largo de los ríos, el límite superior de la zona de establecimiento de plántulas depende de la proximidad de las raíces de las plántulas al nivel freático decreciente. El límite inferior es una función de la elevación máxima de inundación o abrasión. Es posible que las plántulas de álamo negro experimenten una inundación de corto plazo (de 1 a 5 semanas) durante sus primeros años de crecimiento en sistemas hidrológicos naturales y con influencia humana. Estudios anteriores revelaron que la inundación puede explicar más del 70% de la mortalidad de las plántulas durante este tiempo. Mediante experimentos de inundación controlada, encontramos que las plántulas de álamo negro poseen una elevada tolerancia a la inundación de la superficie del suelo y una tolerancia razonable a la inmersión completa del tallo durante una o dos semanas (22% y 50% de mortalidad respectivamente). La mortalidad aumentó en forma lineal con los días de inmersión completa (porcentaje de mortalidad = 4.6 + (2.5 × días de inmersión). La temperatura caliente del agua (25/18 °C día/noche) durante la inmersión completa afectó de manera adversa la biomasa y la supervivencia de las plántulas, lo que resultó en un 64% de mortalidad contra el 39% en temperaturas más frías (18/11 °C día/noche). Nuestros resultados indican que el establecimiento de nuevas poblaciones de álamos negros en el corredor ribereño tendrá mayor éxito cuando los caudales no cubran por completo los tallos de las plántulas por más de dos semanas, y si la temperatura del agua es fría durante la inundación. Desde la perspectiva del manejo de los caudales de los ríos para el reclutamiento de álamos negros, las inundaciones profundas, prolongadas y en temporada tardía son las más perjudiciales. Perennial plant species of semiarid riparian river stage and the beginning of recession ecosystems must tolerate a wide range of water coincide with seed dispersal and germination of conditions ranging from complete submer- riparian trees and shrubs on exposed sediments. gence to drought. Under natural conditions The regeneration of riparian forests depends semiarid riparian zones usually experience first on the ability of the seedlings to extract inundation early in spring followed by gradual sufficient water from root-zone sediments. It soil drainage and a decline of the water table also depends on their ability to keep up with a during the summer (Brinson et al. 1981, Koz - declining water table associated with the reces- lowski 2002, Stella et al. 2006). Early high- sion stage of the river hydrograph (Stromberg 1Department of Land, Air and Water Resources, University of California, Davis, CA 95616. 2Stockholm Environment Institute, 133 D Street, Davis, CA 95616. 3Bureau of Reclamation MidPacific Region, 2800 Cottage Way, Sacramento, CA 95825. 4E-mail: [email protected] 323 324 WESTERN NORTH AMERICAN NATURALIST [Volume 72 et al. 1991, Mahoney and Rood 1992, 1998, reexposed to high light, the potential for Scott et al. 1997, Kranjcec et al. 1998, Rood et oxidative damage to their leaves is high al. 2003). However, depending on the timing (Parolin 2009). Thus, physiological stress may of precipitation, snowmelt rate, dam releases, occur both during and after inundation and and other conditions, seedlings growing along can lead to plant mortality or decreased pro- rivers in spring and summer may be subject to ductivity. Damage and stress can result in short-term flooding (Mahoney and Rood 1998, plant death up to 2 weeks postinundation Amlin and Rood 2001). Thus, regeneration of (Banach et al. 2009). riparian forests depends also on the ability of Considering the stresses and plant acclima- seedlings to survive temporary inundation. tion potential, the severity of physiological This study examines the effects of floodwater effects of inundation on cottonwood seedlings conditions and plant age on the growth and depends on several environmental factors: survival of Fremont cottonwood (Populus fre- duration of inundation, depth of inundation, montii S. Watson ssp. fremontii) seedlings. developmental age of the plant, and water Riparian Fremont cottonwood occurs from temperature during inundation. Hosner (1958, western Texas through New Mexico, Arizona, 1960) observed that complete submergence California, Nevada, and Utah. In mature ripar- for 16 days negatively impacted the survival of ian forests, it is a foundation species, making cottonwood seedlings (among other riparian up a large portion of the biomass and influenc- species). Short-term shoot submergence of 2–4 ing the overall productivity of the ecosystem days led to partial leaf death, whereas 8-day (McBride and Strahan 1984, Warner and Hen- submergence required complete renewal of drix 1984, Stromberg 1993, Rood et al. 2003). the leaf canopy. Sixteen-day submergence led Along the Sacramento River, California, Fre- to death of all seedlings of plains cottonwood mont cottonwood disperses seed that germi- (Populus deltoides; Hosner 1958). A later study nates within 2 days on exposed substrates in from Amlin and Rood (2001) showed that cut- April–May. This seed dispersal is coincident tings of 3 cottonwood species (P. angustifolia, with monthly average peak flows (prior to dam P. balsamifera, and P. deltoides) survived more regulation) of the river’s major tributaries, the than 7 weeks of inundation to the soil surface, Feather and American rivers (USGS 2010a, although dry weight was lower in inundated 2010b). Because Fremont cottonwood estab- treatments compared to controls. lishes close to the river’s edge on exposed Although these studies examined flooding point bars and germinates early in spring, the for different durations, they did not compare seedlings are likely to experience brief inun- the effects of inundation to the soil surface and dation due to either natural or human-induced complete shoot submergence. Complete inun- hydrologic changes. In some years, inundation dation of the shoot is expected to be more has accounted for more than 70% of seedling damaging than partial inundation of the soil mortality during the first year of growth