184 Jacobi et al.: Long-Term Fluctuations in Water Status and Crown Dieback of Plains Cottonwood Trees dieback taken in the last week of August to the second week of September are sufficient to monitor the water status and future health of cottonwoods in Front Range Colorado. • If spring water (May–June) is provided and then supplemental water is provided again in July or August (because cottonwood trees become moderately water-stressed in one to two months aſter water is provided in the spring), trees can be expected to survive. Other key findings important to maintaining healthy cottonwood trees in urban environments: • Summer precipitation should not be relied upon to relieve water stress for longer than one week in cottonwoods. • Soil moisture readings are not easy to obtain, nor are they good proxies of the predawn water status of cottonwoods. additional • Providing water to the root zones of cottonwood trees dur- ing periods of below-normal precipi- tation can minimize crown dieback. Acknowledgments. We would like to thank the following indi- viduals for their contributions: L. Van Alyne, H.O. Jacobi, E.F. Jacobi, C.B. Preston for technical assistance, G.E. Cardon and D. Cooper for water and soil-moisture advice, J. zumBrunnen and P. Turk for statistical assistance (Colorado State Univer- sity, Franklin A. Graybill Statistical Laboratory), M. Bowers, J. Foster, D. Kennedy, J. Loran, G. Martinez, and T. Mulligan for funding, and technical and logistical support at Denver Water. This study was funded by Denver Water and Colorado State University, Agricultural Experiment Station. LITERATURE CITED Amlin, N.M., and S.B. Rood. 2003. Drought stress and recovery of riparian cottonwoods due to water table alteration along Willow Creek, Alberta. Trees 17:351–358. Coble, A.P., and T.E Kolb. 2012. Riparian tree growth response to drought and altered streamflow along the Dolores River, Colo- rado. Western Journal of Applied Forestry 27:205–211. Cooper, D.J., D.R. D’Amico, and M.L. Scott. 2003. Physiological and morphological response patterns of Populus deltoides to alluvial groundwater pumping. Environmental Management 31:215–226. Cox, G., D. Fisher, S.C. Hart, and T.G Whitham. 2005. Nonresponse of native cottonwood trees to water additions during summer drought. Western North American Naturalist 65:175–185. Donovan, L., M. Linton, and J. Richards. 2001. Predawn plant water potential does not necessarily equilibrate with soil water poten- tial under well-watered conditions. Oecologia 129:328–335. Fichot, R., F. Brignolas, H. Cochard, and R. Ceulemans. 2015. Vulnerability to drought-induced cavitation in poplars: Syn- thesis and future opportunities. Plant, Cell, and Environment 38:1233–1251. Horton, J.L., S.C. Hart, and T.E Kolb. 2003. Physiological condition and water source use of Sonoran desert riparian trees at the Bill Williams River, Arizona, USA. Isotopes Environmental Health Studies 39:69–82. Horton, J.L., T.E. Kolb, and S.C. Hart. 2001. Responses of riparian trees to interannual variation in ground water depth in a semi- arid river basin. Plant, Cell, and Environment 24:293–304. Jones, H.G. 1990. Physiological aspects of the control of water status in horticultural crops. HortScience 25:19–26. Kramer, P.J., and T.T. Kozlowski. 1979. Physiology of Woody Plants. Academic Press, Cambridge, Massachusetts, U.S. 811 pp. Leffler, A.J., L.E. England, and J. Naito. 2000. Vulnerability of Fre- mont cottonwood (Populus fremontii Wats.) individuals to xy- lem cavitation. Western North American Naturalist 60:204–210. Rood, S.B., and J.M. Mahoney.1995. River damming and riparian cottonwoods along the Marias River, Montana. Rivers 5:195–207. Rood, S.B., J.H. Braatne, and F.M.R. Hughes. 2003. Ecophysiology of riparian cottonwoods: Stream flow dependency, water rela- tions and restoration. Tree Physiology 23:1113–1124. Schulte, P.J., T.M. Hinckley, and R.F. Stettler. 1987. Stomatal re- sponses of Populus to leaf water potential. Canadian Journal of Botany 65:255–260. Scott, M.L., P.B. Shafroth, and G.T. Auble. 1999. Responses of ripar- ian cottonwoods to alluvial water table declines. Environmental Management 23:347–358. Sellin, A. 1999. Does pre-dawn water potential reflect conditions of equilibrium in plant and soil water status? Acta Oecol 20:51–59. Skari, D. 2003. High Line Canal Meandering Through Time. C & M Press, Denver, Colorado, U.S. 158 pp. Tyree, M.T., K.J. Kolb, S.B. Rood, and S. Patiño. 1994. Vulnerability to drought-induced cavitation of riparian cottonwoods in Al- berta: A possible factor in the decline of the ecosystem? Tree Physiology 14:455–466. Williams, C.A., and D.J Cooper. 2005. Mechanisms of riparian cot- tonwood decline along regulated rivers. Ecosystems 8:382–395. Williams, L.E., and F.J. Araujo. 2002. Correlations among predawn leaf, midday leaf, and midday stem water potential and their correlations with other measures of soil and plant water status in Vitis vinifera. Journal of the American Society for Horticultural Science 127:448–454. William R. Jacobi (corresponding author) Department of Bioagricultural Sciences and Pest Management Colorado State University Fort Collins, Colorado 80523, U.S.
[email protected] Ronda D. Koski Department of Horticulture and Landscape Architecture Colorado State University Fort Collins, Colorado 80523, U.S. Betsy A. Goodrich USDA Forest Service, Forest Health Protection, Wenatchee Insect and Disease Service Center Okanogan-Wenatchee NF 1133 N. Western Ave Wenatchee, Washington 98001, U.S. ©2017 International Society of Arboriculture
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