Kiyomi Morino

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• Roos, C. I., Kaib, J. M., Laluk, N. C., Adams, M. M., Guiterman, C. H., Baisan, C. H., Morino, K., & Swetnam, T. W. (2025). Tree rings reveal persistent Western Apache (Ndee) fire stewardship and niche construction in the American Southwest. Proceedings of the National Academy of Sciences of the United States of America, 122(Issue 32). doi:10.1073/pnas.2509169122
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  Identifying the influence of low-density Indigenous populations in paleofire records has been methodologically challenging. In the Southwest United States, well-replicated fire histories suggest that abundant lightning and suitable climate conditions drove frequent low-severity wildfires in dry pine forests independent of human activities even as ethnography provided hints that highly mobile indigenous populations used fire in myriad land use contexts. Here, we leverage published and unpublished tree-ring fire history records from pine forests in Western Apache (Ndee) traditional territory in central and eastern Arizona (N = 34 sites, N = 649 trees) to demonstrate that historical fire regimes were overwhelmingly influenced by Ndee cultural burning. Our tree-ring synthesis shows significantly more frequent fires in Ndee territory than elsewhere in the region for centuries before the establishment of reservations (1600–1870 CE). Despite the heightened fire activity, fires were largely small and asynchronous, occurred disproportionately in late April and May, when Ndee invested significant subsistence activities in these pine forests, and occurred independent of climate drivers. This suggests that Ndee fire stewardship created a patchwork of nearly annual small, spring fires that inhibited natural fire spread and limited the influence of drought on fire activity. Our work shows that even relatively small, highly mobile populations of forager-gardeners had significant influence on some pre-Euroamerican fire regimes despite abundant natural ignitions. Our study shows clearly that Indigenous fire management impacted fire-size distributions, fire frequencies, and fire seasonality in ways that cannot be explained by seasonal and annual lightning densities.
• Enquist, B. J., Thomaz, L. D., Sonsin-oliveira, J., Morino, K., Milanez, C. R., Lourenco, J., & Arx, G. V. (2022). Hydraulic tradeoffs underlie local variation in tropical forest functional diversity and sensitivity to drought.. The New phytologist, 234(1), 50-63. doi:10.1111/nph.17944
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  Tropical forests are important to the regulation of climate and the maintenance of biodiversity on Earth. However, these ecosystems are threatened by climate change, as temperatures rise and droughts' frequency and duration increase. Xylem anatomical traits are an essential component in understanding and predicting forest responses to changes in water availability. We calculated the community-weighted means and variances of xylem anatomical traits of hydraulic and structural importance (plot-level trait values weighted by species abundance) to assess their linkages to local adaptation and community assembly in response to varying soil water conditions in an environmentally diverse Brazilian Atlantic Forest habitat. Scaling approaches revealed community-level tradeoffs in xylem traits not observed at the species level. Towards drier sites, xylem structural reinforcement and integration balanced against hydraulic efficiency and capacitance xylem traits, leading to changes in plant community diversity. We show how general community assembly rules are reflected in persistent fiber-parenchyma and xylem hydraulic tradeoffs. Trait variation across a moisture gradient is larger between species than within species and is realized mainly through changes in species composition and abundance, suggesting habitat specialization. Modeling efforts to predict tropical forest diversity and drought sensitivity may benefit from adding hydraulic architecture traits into the analysis.
• Morino, K., Hughes, M. K., Morino, K., Minor, R. L., Hughes, M. K., Brown, P. M., & Barron-gafford, G. A. (2021). Bimodal cambial activity and false-ring formation in conifers under a monsoon climate.. Tree physiology, 41(10), 1893-1905. doi:10.1093/treephys/tpab045
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  Tracking wood formation in semiarid regions during the seasonal march of precipitation extremes has two important applications. It can provide (i) insight into the adaptive capacities of trees to drought and (ii) a basis for a richer interpretation of tree-ring data, assisting in a deeper understanding of past and current climate. In the southwestern USA, the anatomical signature of seasonally bimodal precipitation is the 'false ring'-a band of latewood-like cells in the earlywood. These occur when a particularly deep drought during the early growing season ends abruptly with timely, mid-growing season monsoonal rains. Such conditions presented in southern Arizona in 2014, enabling us to explore false-ring formation in ponderosa pine (Pinus ponderosa Lawson and C. Lawson) and Douglas-fir (Pseudotsuga menziesii Mirb. Franco) in mixed-conifer forest at 2573 m above sea level. We ask: what were the cell-by-cell timings and durations in the phases of wood cell development in 2014? How do these seasonal patterns relate to strongly fluctuating environmental conditions during the growing season? We took weekly microcores from March through November from six ponderosa pine and seven Douglas-fir trees at a well-instrumented flux tower site. Thin sections were prepared, and we counted cells in cambial, expansion, cell wall thickening and mature phases. For ponderosa pine trees forming a false ring, the first impact of intensifying seasonal drought was seen in the enlarging phase and then, almost a month later, in cambial activity. In this species, recovery from drought was associated with recovery first in cambial activity, followed by cell enlargement. This timing raised the possibility that cell division may be affected by atmospheric moisture increases before soil recharge. In both species, the last false-ring cells matured during the summer rainy season. Bimodal cambial activity coincident with moisture availability was observed in both species, whether or not they formed a false ring. This deeper knowledge of the precise timing of both developmental and environmental events should help define mechanistic connections among these factors in creating bimodal growth patterns.
• Belmecheri, S., Wright, W. E., Szejner, P., Morino, K. A., & Monson, R. K. (2018). Carbon and oxygen isotope fractionations in tree rings reveal interactions between cambial phenology and seasonal climate.. Plant, cell & environment, 41(12), 2758-2772. doi:10.1111/pce.13401
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  We developed novel approaches for using the isotope composition of tree-ring subdivisions to study seasonal dynamics in tree-climate relations. Across a 30-year time series, the δ13 C and δ18 O values of the earlywood (EW) cellulose in the annual rings of Pinus ponderosa reflected relatively high intrinsic water-use efficiencies and high evaporative fractionation of 18 O/16 O, respectively, compared with the false latewood (FLW), summerwood (SW), and latewood (LW) subdivisions. This result is counterintuitive, given the spring origins of the EW source water and midsummer origins of the FLW, SW, and LW. With the use of the Craig-Gordon (CG), isotope-climate model revealed that the isotope ratios in all of the ring subdivision are explained by the existence of seasonal lags, lasting several weeks, between the initial formation of tracheids and the production of cellulosic secondary cell walls during maturation. In contrast to some past studies, modification of the CG model according to conventional methods to account for mixing of needle water between fractionated and nonfractionated sources did not improve the accuracy of predictions. Our results reveal new potential in the use of tree-ring isotopes to reconstruct past intra-annual tree-climate relations if lags in cambial phenology are reconciled with isotope ratio observations and included in theoretical treatments.
• Szejner, P., Belmecheri, S., Morino, K. A., Wright, W. E., & Monson, R. K. (2018). Finding the seasons in tree ring stable isotope ratios.. American journal of botany, 105(5), 819-821. doi:10.1002/ajb2.1083
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  The annual diameter increments of tree rings provide insight into past climate influences on tree growth, wildfire intervals, insect outbreaks, and the history of human civilizations (Stahle and Dean, 2011). Most recently, decadal-to-millennial tree-ring records have been used as foundational paleoclimate proxies in assessments and reports from the United Nations Intergovernmental Panel on Climate Change (IPCC). An inherent assumption in the use of tree rings to reconstruct tree–climate interactions is that the activities of stem cambial cells and their derivatives are modulated in response to environmental resource limitations and climate variations and that the modulated responses are predictable. These relations have been recognized since at least the 16th century. For example, Leonardo da Vinci wrote: “The rings around the branches of the sawn trees show the number of years and which were formed in the wetter or drier years by their greater or lesser thickness” (translated generally from the Trattato della pittura; Manzi, 1817, p. 396, see Sarton, 1954). Over the subsequent four centuries, anecdotal observations on the correlations between climate and tree rings gradually coalesced into the discipline of dendrochronology, with the modern form of the discipline emerging in the early 20th century under the leadership of A. E. Douglass at the University of Arizona. Here, we highlight some recent discoveries in one part of dendrochronology, known as dendroclimatology, which have allowed us to extract details about seasonal climate variations during past decades and their influences on forest ecophysiology. With this capability, we are on the cusp of accessing even greater insights about the nature of past climate cycles, their influences on forest productivity and the feedbacks within forest–climate interactions that will determine future climate regimes on Earth. In past dendroclimatological studies, the focus has most often been on inter-annual variation in climate. Recent studies have revealed even greater resolution in the anatomical structure and chemical composition of tree rings, such that we can now recognize the patterns and causes of intra-annual (seasonal) dynamics in tree–climate interactions (Leavitt et al., 2011; Cuny and Rathgeber, 2016; Rinne et al., 2015). The knowledge that specific anatomical zones within individual rings reflect seasonal variation in climate is not new. In past studies, seasonal variation in cambial activity has been inferred through the recognition of earlywood and latewood tissues, which are assumed to reflect growth during the earlier and later parts of the growing season, respectively (Meko and Baisan, 2001; Pallardy, 2008). What is new, however, is the use of various techniques to cut or ablate thin sections of cellulose from across individual rings and molecular techniques to infer kinetic patterns in tree physiological processes (Loader et al., 2017). These finely resolved serial sections allow us to assess tree–climate interactions at scales of days to weeks, and we can identify seasonal patterns in the use of environmental resources and climate space, such as those defined by precipitation and temperature and nutrient resources stored in the trees (Rinne et al., 2015). In essence, we can much more accurately “find the seasons in tree rings”. We have been studying the stable isotope ratios of selected compounds (13CO2/12CO2 and 2H1HO/1H2O or H218O/H216O) that are incorporated into tree-ring cellulose in Pinus ponderosa trees distributed across the geographic domain defined by the North American monsoon climate system (Szejner et al., 2016). When pine needles assimilate atmospheric CO2 through photosynthesis or lose H2O through transpiration, isotopic ratios of the elements that compose these compounds are altered through the process of isotopic discrimination—i.e., the heavier and lighter isotope forms of compounds (known as isotopomers) are distinguished through biochemical and physical processes (Gessler et al., 2014). To align the seasonal determinants of isotope discrimination with specific components of a tree ring, we sample sections from the earliest earlywood (EW1), later earlywood (EW2), false latewood (FLW, embedded within the earlywood), summer wood (SW, the earlywood that follows the FLW) and latewood (LW) (Fig. 1), thus, providing five seasonal fractions for each annual ring. Our initial studies in southern Arizona revealed a unique and puzzling pattern. Based on theory (see Saurer et al., 1997), the lowest ratios of the heavier to lighter stable isotopes (13C/12C and 18O/16O) were predicted to occur in the earlywood (EW1 and EW2), which is produced during spring. We hypothesized that with cooler springtime temperatures, higher relative humidities, and ample supply of snowmelt water, the production of photosynthate to support cambial activity would occur at a lower leaf-to-atmosphere water vapor pressure difference (VPD) and higher steady-state ratios of intercellular to ambient CO2 concentration (ci/ca), both of which favor discrimination leading to lighter isotope ratios in tree-ring cellulose. These conditions are predicated on the assumption that during favorable seasonal moisture regimes, a cooler more humid atmosphere is associated with reduced transpiration rates at any given stomatal conductance (gs), and a lower intrinsic water-use efficiency (iWUE = A/gs, where A is net CO2 assimilation rate). In contrast, the highest 13C/12C and 18O/16O ratios (and highest iWUE) were predicted to be found in the FLW band. The small cells and high density of the FLW band are known to be produced during the early-summer, hyper-arid phase, presumably in response to seasonal drought (Leavitt et al., 2011). The lower gs and ci/ca ratios that are often observed during drought should favor discrimination leading to heavier isotope ratios in tree-ring cellulose. With the start of monsoon rains, in mid-summer, we hypothesized that the increased availability of water would be reflected in a return to lighter isotope ratios in the cellulose of SW and LW. In contrast to these hypothesized patterns, however, we observed that the EW1 and EW2 fractions contained the heaviest cellulose isotope ratios, reflecting the highest seasonal iWUE and highest seasonal VPDs, presumably due to the use of photosynthate that was produced during periods with limited soil moisture, a dry atmosphere, and warm temperatures (S. Belmecheri and P. Szejner, unpublished data). The isotope ratios of the FLW band were isotopically among the lightest of the entire annual ring, presumably reflecting the use of photosynthate produced in a climate with wetter soil and more humid atmospheric conditions. The SW and LW cells contained isotope ratios that were heavier than in the FLW, but lighter than in the EW1 and EW2 bands. What could cause the apparent paradoxes between the predicted and observed patterns? Insight came when Kiyomi Morino, Ed Wright, and Malcolm Hughes, of the Laboratory of Tree Ring Research in Tucson, took a closer look at the phenology of cambial processes. Their observations confirmed the formation of EW cells during cooler springtime weather. However, tracheids mature during the subsequent weeks that extend well into the hot, early-summer drought. Thus, while the large-diameter cell size of EW reflects springtime production, the stable isotope composition of mature EW reflects hotter, drier summer weather. The fact that the phases of xylogenesis occur across many weeks is well established (Skene 1969), to the point of being “textbook knowledge” (Pallardy 2008). However, refinement of that knowledge to align specific phases of xylogenesis to the seasonal timing of photosynthate production, and its reflection in the stable isotope record of cellulose, has only recently emerged. In one recent high-profile report, Cuny et al. (2015) reported that lags between annual increases in stem girth and woody biomass average 1 month in many global forests. This discovery called into question the use of tree-ring diameter measurements to indicate seasonal patterns in woody biomass production in analyses and models of the global carbon cycle. In the past, limited awareness of how the seasonal phenology of xylogenesis lines up with specific radial components of annual rings has been noted as contributing to “fuzziness” in interpretations of isotope-environment correlations (Leavitt et al., 2011). As a result, seasonal analyses of tree-ring isotope ratios have focused on the earliest EW or latest LW as the most reliable markers of seasonal climate (e.g., Leavitt et al., 2011; Rinne et al., 2015). With a quantitative understanding of seasonal lags during xylogenesis, we can achieve more accurate assessments of seasonality across the entire ring. Having resolved the mystery of the gap between anatomy and isotope composition, we are now in a position to address several aspects of tree–climate interactions. In ponderosa pine, for example, which is widely distributed across the western United States, we can begin to dissect the independent influences of winter versus summer precipitation and seasonal droughts on forest tree growth and water use. We can also assess the potential for long-lasting effects due to extreme seasonal climates (e.g., the multi-year legacies of extreme droughts). Going forward, one of our more salient needs will be to expand these perspectives to include additional species. Broadleaf, deciduous trees, for example, often utilize stored carbohydrate resources to support construction of the earliest EW and latest LW when photosynthetic production is seasonally constrained. The dependence on stored photosynthate for seasonal wood production in deciduous trees can obscure efforts to extract seasonal insight on tree–climate stable isotope connections (Helle and Schleser, 2004). The clearest opportunities at the moment for elucidating isotope–climate relations through serial tree-ring analyses appear to lie with needle-leaf, evergreen conifers, especially those in the Pinaceae (Barbour et al., 2002; Leavitt et al., 2011; Rinne et al., 2015). Tree rings continue to inspire curiosity about how some of the oldest organisms on the planet accommodate and record their surrounding environment. There is growing recognition that the annual rings of trees contain considerably more information about their environment than what is determined from diameter increments alone. As molecular analytical techniques improve, it is likely that we will be able to deconstruct the glucose units that compose cellulose and extract even more insight about the seasonality of woody biomass production (Augusti and Schleucher, 2007). Recently, the resolution of isotope ratios in specific thin sections of tree rings has improved with the use of laser ablation techniques coupled to in-line combustion and mass spectrometery. Now, we are able to assess isotope ratios of samples in the diameter range of 40–100 μm (Rinne et al., 2015; Loader et al., 2017). The seasonal resolution capabilities of such systems are currently limited by the sample size required for isotope ratio resolution. As the analytical capabilities for assessing isotope ratios in extremely small samples improves, the seasonal resolution capabilities of tree-ring analysis will likely also improve. We thank the two anonymous reviewers for helpful comments and recommendations. Professors Malcolm Hughes and Steven Leavitt (University of Arizona) provided valuable discussions and recommendations throughout this line of research.
• Woodhouse, C. A., Pederson, G. T., Morino, K., Mcafee, S. A., & Mccabe, G. J. (2016). Increasing influence of air temperature on upper Colorado River streamflow. Geophysical Research Letters, 43(5), 2174-2181. doi:10.1002/2015gl067613
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  This empirical study examines the influence of precipitation, temperature, and antecedent soil moisture on upper Colorado River basin (UCRB) water year streamflow over the past century. While cool season precipitation explains most of the variability in annual flows, temperature appears to be highly influential under certain conditions, with the role of antecedent fall soil moisture less clear. In both wet and dry years, when flow is substantially different than expected given precipitation, these factors can modulate the dominant precipitation influence on streamflow. Different combinations of temperature, precipitation, and soil moisture can result in flow deficits of similar magnitude, but recent droughts have been amplified by warmer temperatures that exacerbate the effects of relatively modest precipitation deficits. Since 1988, a marked increase in the frequency of warm years with lower flows than expected, given precipitation, suggests continued warming temperatures will be an increasingly important influence in reducing future UCRB water supplies.
• Woodhouse, C., Pederson, G., Morino, K., McAfee, S., & McCabe, G. (2016). Increasing influence of air temperature on upper Colorado River streamflow. Geophysical Research Letters, 43(5). doi:10.1002/2015GL067613
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  This empirical study examines the influence of precipitation, temperature, and antecedent soil moisture on upper Colorado River basin (UCRB) water year streamflow over the past century. While cool season precipitation explains most of the variability in annual flows, temperature appears to be highly influential under certain conditions, with the role of antecedent fall soil moisture less clear. In both wet and dry years, when flow is substantially different than expected given precipitation, these factors can modulate the dominant precipitation influence on streamflow. Different combinations of temperature, precipitation, and soil moisture can result in flow deficits of similar magnitude, but recent droughts have been amplified by warmer temperatures that exacerbate the effects of relatively modest precipitation deficits. Since 1988, a marked increase in the frequency of warm years with lower flows than expected, given precipitation, suggests continued warming temperatures will be an increasingly important influence in reducing future UCRB water supplies.
• Morino, K., Brekke, L. D., Cayan, D. R., Das, T., Hartmann, H. C., Hidalgo, H. G., Hoerling, M. P., Lettenmaier, D. P., Mccabe, G. J., Overpeck, J. T., Udall, B., Vano, J. A., Webb, R. S., & Werner, K. (2014). Understanding Uncertainties in Future Colorado River Streamflow. Bulletin of the American Meteorological Society, 95(1), 59-78. doi:10.1175/bams-d-12-00228.1
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  The Colorado River is the primary water source for more than 30 million people in the United States and Mexico. Recent studies that project streamf low changes in the Colorado River all project annual declines, but the magnitude of the projected decreases range from less than 10% to 45% by the mid-twenty-first century. To understand these differences, we address the questions the management community has raised: Why is there such a wide range of projections of impacts of future climate change on Colorado River streamflow, and how should this uncertainty be interpreted? We identify four major sources of disparities among studies that arise from both methodological and model differences. In order of importance, these are differences in 1) the global climate models (GCMs) and emission scenarios used; 2) the ability of land surface and atmospheric models to simulate properly the high-elevation runoff source areas; 3) the sensitivities of land surface hydrology models to precipitation and temperature changes; ...
• Vano, J., Udall, B., Cayan, D., Overpeck, J., Brekke, L., Das, T., Hartmann, H., Hidalgo, H., Hoerling, M., McCabe, G., Morino, K., Webb, R., Werner, K., & Lettenmaier, D. (2014). Understanding uncertainties in future Colorado River streamflow. Bulletin of the American Meteorological Society, 95(1). doi:10.1175/BAMS-D-12-00228.1
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  The Colorado River is the primary water source for more than 30 million people in seven rapidly growing, mostly arid American states and Mexico. The Colorado River water supply system, which consists of two large reservoirs (Lakes Mead and Powell) and numerous smaller reservoirs, is already stressed because of growing water demand and an ongoing drought that is outside the historical norm of twentieth-century climate variability (Fulp 2005; USBR 2011a). Concerns have been voiced that this recent prolonged drought could be a harbinger of a permanent shift to a drier climate (Seager et al. 2007; Barnett and Pierce 2008, 2009; Overpeck and Udall 2010; Cayan et al. 2010; USBR 2011a, among others).
• Glenn, E. P., Nagler, P. L., Morino, K., & Hultine, K. R. (2013). Erratum to: Phreatophytes under stress: Transpiration and stomatal conductance of saltcedar (Tamarix spp.) in a high-salinity environment (Plant Soil, 10.1007/s11104-013-1803-0). Plant and Soil, 371(Issue 1-2). doi:10.1007/s11104-013-1848-0
• Glenn, E. P., Nagler, P. L., Morino, K., & Hultine, K. R. (2013). Phreatophytes under stress: transpiration and stomatal conductance of saltcedar ( Tamarix spp.) in a high-salinity environment. Plant and Soil, 371(1), 655-672. doi:10.1007/s11104-013-1803-0
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  We sought to understand the environmental constraints on an arid-zone riparian phreatophtye, saltcedar (Tamarix ramosissima and related species and hybrids), growing over a brackish aquifer along the Colorado River in the western U.S. Depth to groundwater, meteorological factors, salinity and soil hydraulic properties were compared at stress and non-stressed sites that differed in salinity of the aquifer, soil properties and water use characteristics, to identify the factors depressing water use at the stress site. Saltcedar leaf-level transpiration (EL), LAI, and stomatal conductance (GS) were measured over a growing season (June–September) with Granier and stem heat balance sensors and were compared to those for saltcedar at the non-stress site determined in a previous study. Transpiration on a ground-area basis (EG) was calculated as EL × LAI. Environmental factors were regressed against hourly and daily EL and GS at each site to determine the main factors controlling water use at each site. At the stress site, mean EG over the summer was only 30 % of potential evapotranspiration (ETo). GS and EG peaked between 8 and 9 am then decreased over the daylight hours. Daytime GS was negatively correlated with vapor pressure deficit (VPD) (P < 0.05). By contrast, EG at the non-stress site tracked the daily radiation curve, was positively correlated with VPD and was nearly equal to ETo on a daily basis. Depth to groundwater increased over the growing season at both sites and resulted in decreasing EG but could not explain the difference between sites. Both sites had high soil moisture levels throughout the vadose zone with high calculated unsaturated conductivity. However, salinity in the aquifer and vadose zone was three times higher at the stress site than at the non-stress site and could explain differences in plant EG and GS. Salts accumulated in the vadose zone at both sites so usable water was confined to the saturated capillary fringe above the aquifer. Existence of a saline aquifer imposes several types of constraints on phreatophyte EG, which need to be considered in models of plant water uptake. The heterogeneous nature of saltcedar EG over river terraces introduces potential errors into estimates of ET by wide-area methods.
• Nagler, P. L., Glenn, E. P., Morino, K., & Hultine, K. R. (2013). Phreatophytes under stress: review of studies on transpiration and stomatal conductance of Tamarix across a western US floodplain. Acta Horticulturae, 61-66. doi:10.17660/actahortic.2013.991.7
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  Transpiration (E(L)) and stomatal conductance (G(S)) were measured with stem heat-balance and Granier sap flux sensors on the dominant phreatophyte, saltcedar (Tamarix spp.), growing at six sites on a floodplain on the Lower Colorado River, US. Plant-specific leaf area index (LAPS) of shrubs was measured by leaf harvesting and Licor 2000 Plant Canopy Analyzer, and fractional cover (f(c)) was estimated by aerial imagery. Ground-area transpiration (E(G)) was calculated as E(L) × LAPS × f(c). The sites presented environmental gradients with respect to distance from the river (0.2-1.5 km), depth to groundwater (2.4-3.5 m), groundwater salinity [1.9-24.0 g L-1 Total Dissolved Solids (TDS)] and soil texture (ranging from sand to clayey silts). E(L) varied from 1-3 mm m-1 leaf d-1 across sites, while LAPS ranged more narrowly, from 2-4, and f(c) varied from 0.5-0.95. Due to differences in E(L), LAPS and f(c), EG ranged from 1.2-9.5 mm d-1, nearly a 10-fold range. Only one site had E(G) characteristic of unstressed condition. We concluded that saltcedar is capable of high E(G) rates, but is also a stress adapted species, with E(G) highly variable over non-flooding riparian zones typical of regulated rivers. Salinity of the aquifer and vadose zone were identified as key constraints on saltcedar E(G). Mean E(G) over the floodplain was only 40% of potential (ET), contrary to earlier assumptions that saltcedar is invariably a high-water use plant.
• Nagler, P., Glenn, E., Morino, K., & Hultine, K. (2013). Phreatophytes under stress: Review of studies on transpiration and stomatal conductance of Tamarix across a Western US floodplain. Acta Horticulturae, 991. doi:10.17660/ActaHortic.2013.991.7
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  Transpiration (EL) and stomatal conductance (GS) were measured with stem heat-balance and Granier sap flux sensors on the dominant phreatophyte, saltcedar (Tamarix spp.), growing at six sites on a floodplain on the Lower Colorado River, US. Plant-specific leaf area index (LAPS) of shrubs was measured by leaf harvesting and Licor 2000 Plant Canopy Analyzer, and fractional cover (fc) was estimated by aerial imagery. Ground-area transpiration (EG) was calculated as EL × LAPS × fc. The sites presented environmental gradients with respect to distance from the river (0.2-1.5 km), depth to groundwater (2.4-3.5 m), groundwater salinity [1.9-24.0 g L-1 Total Dissolved Solids (TDS)] and soil texture (ranging from sand to clayey silts). EL aried from 1-3 mm m-1 leaf d-1 across sites, while LAPS ranged more narrowly, from 2-4, and fc varied from 0.5-0.95. Due to differences in EL, LAPS and fc, EG ranged from 1.2-9.5 mm d-1, nearly a 10-fold range. Only one site had EG characteristic of unstressed condition. We concluded that saltcedar is capable of high EG rates, but is also a stress adapted species, with E G highly variable over nonflooding riparian zones typical of regulated rivers. Salinity of the aquifer and vadose zone were identified as key constraints on saltcedar EG. Mean EG over the floodplain was only 40% of potential ET, contrary to earlier assumptions that saltcedar is invariably a high-water use plant. © ISHS 2013.
• Glenn, E. P., Morino, K., Nagler, P. L., Murray, R. S., Pearlstein, S., & Hultine, K. R. (2012). Roles of saltcedar (Tamarix spp.) and capillary rise in salinizing a non-flooding terrace on a flow-regulated desert river. Journal of Arid Environments, 79, 56-65. doi:10.1016/j.jaridenv.2011.11.025
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  Abstract Tamarix spp. (saltcedar) secretes salts and has been considered to be a major factor contributing to the salinization of river terraces in western US riparian zones. However, salinization can also occur from the capillary rise of salts from the aquifer into the vadose zone. We investigated the roles of saltcedar and physical factors in salinizing the soil profile of a non-flooding terrace at sites on the Cibola National Wildlife Refuge on the Lower Colorado River, USA. We placed salt traps under and between saltcedar shrubs and estimated the annual deposition rate of salts from saltcedar. These were then compared to the quantities and distribution on of salts in the soil profile. Dense stands of saltcedar deposited 0.159 kg m−2 yr−1 of salts to the soil surface. If this rate was constant since seasonal flooding ceased in 1938 and all of the salts were retained in the soil profile, they could account for 11.4 kg m−2 of salt, about 30% of total salts in the profile today. Eliminating saltcedar would not necessarily reduce salts, because vegetation reduces the upward migration of salts in bulk flow from the aquifer. The densest saltcedar stand had the lowest salt levels in the vadose zone in this study.
• Woodhouse, C. A., Morino, K., & Meko, D. M. (2012). Dendrochronology and links to streamflow. Journal of Hydrology, 412, 200-209. doi:10.1016/j.jhydrol.2010.11.041
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  Summary Streamflow variability on timescales of decades to centuries becomes increasingly important as water managers grapple with shortages imposed by increasing demand and limited supply, and possibly exacerbated by climate change. ► Two applications of dendrochronology to the study of flow variability are illustrated for an existing 1244-yr reconstruction of annual flows of the Colorado River at Lees Ferry, Arizona, USA: (1) identification and climatological interpretation of rare flow events, and (2) assessment of vulnerability of water-supply systems to climatic variability. ► Analysis centers on a sustained drought of the mid-1100s characterized by persistent low flows on both the Colorado and Sacramento Rivers. ► Analysis of geopotential height anomalies during modern joint-droughts suggests more than one mode of circulation might accompany joint-drought in the two basins. ► Monte Carlo simulation is used to demonstrate that a drought as severe as that in the 1100s on the Colorado River might be expected about once in every 4–6 centuries by chance alone given the time-series properties of the modern gaged flows. Application of a river-management model suggests a mid-1100s-style drought, were it to occur today, would drop reservoir levels in Lake Mead to dead-pool within a few decades. ► Uncertainty presents challenges to accurately quantifying severe sustained droughts from streamflow reconstructions, especially early in the tree-ring record. ► Corroboration by multiple proxy records is essential. ► Future improvements are likely to require a combination of methodological advancements and expanded basic data.
• Doody, T. M., Nagler, P. L., Glenn, E. P., Moore, G. W., Morino, K., Hultine, K. R., & Benyon, R. G. (2011). Potential for water salvage by removal of non‐native woody vegetation from dryland river systems. Hydrological Processes, 25(26), 4117-4131. doi:10.1002/hyp.8395
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  Globally, expansion of non-native woody vegetation across floodplains has raised concern of increased evapotranspiration (ET) water loss with consequent reduced river flows and groundwater supplies. Water salvage programs, established to meet water supply demands by removing introduced species, show little documented evidence of program effectiveness. We use two case studies in the USA and Australia to illustrate factors that contribute to water salvage feasibility for a given ecological setting. In the USA, saltcedar (Tamarix spp.) has become widespread on western rivers, with water salvage programs attempted over a 50-year period. Some studies document riparian transpiration or ET reduction after saltcedar removal, but detectable increases in river base flow are not conclusively shown. Furthermore, measurements of riparian vegetation ET in natural settings show saltcedar ET overlaps the range measured for native riparian species, thereby constraining the possibility of water salvage by replacing saltcedar with native vegetation. In Australia, introduced willows (Salix spp.) have become widespread in riparian systems in the Murray–Darling Basin. Although large-scale removal projects have been undertaken, no attempts have been made to quantify increases in base flows. Recent studies of ET indicate that willows growing in permanently inundated stream beds have high transpiration rates, indicating water savings could be achieved from removal. In contrast, native Eucalyptus trees and willows growing on stream banks show similar ET rates with no net water salvage from replacing willows with native trees. We conclude that water salvage feasibility is highly dependent on the ecohydrological setting in which the non-native trees occur. We provide an overview of conditions favorable to water salvage. Copyright © 2011 John Wiley & Sons, Ltd.
• Hartwell, S., Morino, K., Nagler, P. L., & Glenn, E. P. (2010). On the irrigation requirements of cottonwood (Populus fremontii and Populus deltoides var. wislizenii) and willow (Salix gooddingii) grown in a desert environment. Journal of Arid Environments, 74(6), 667-674. doi:10.1016/j.jaridenv.2009.12.007
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  Abstract Native tree plots have been established in river irrigation districts in the western U.S. to provide habitat for threatened and endangered birds. Information is needed on the effective irrigation requirements of the target species. Cottonwood (Populus spp.) and willow (Salix gooddingii) trees were grown for seven years in an outdoor plot in a desert environment in Tucson, Arizona. Plants were allowed to achieve a nearly complete canopy cover over the first four years, then were subjected to three daily summer irrigation schedules of 6.20 mm d−1; 8.26 mm d−1 and 15.7 mm d−1. The lowest irrigation rate was sufficient to maintain growth and high leaf area index for cottonwoods over three years, while willows suffered considerable die-back on this rate in years six and seven. These irrigation rates were applied April 15–September 15, but only 0.88 mm d−1 was applied during the dormant period of the year. Expressed as a fraction of reference crop evapotranspiration (ETo), recommended annual water applications plus precipitation (and including some deep drainage) were 0.83 ETo for cottonwood and 1.01 ETo for willow. Current practices tend to over-irrigate restoration plots, and this study can provide guidelines for more efficient water use.
• Hultine, K. R., Nagler, P. L., Morino, K., Bush, S. E., Burtch, K. G., Dennison, P. E., Glenn, E. P., & Ehleringer, J. R. (2010). Sap flux-scaled transpiration by tamarisk (Tamarix spp.) before, during and after episodic defoliation by the saltcedar leaf beetle (Diorhabda carinulata). Agricultural and Forest Meteorology, 150(11), 1467-1475. doi:10.1016/j.agrformet.2010.07.009
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  The release of the saltcedar beetle (Diorhabda carinulata) has resulted in the periodic defoliation of tamarisk (Tamarix spp.) along more than 1000 river km in the upper Colorado River Basin and is expected to spread along many other river reaches throughout the upper basin, and possibly into the lower Colorado River Basin. Identifying the impacts of these release programs on tamarisk water use and subsequent water cycling in arid riparian systems are largely unknown, due in part to the difficulty of measuring water fluxes in these systems. We used lab-calibrated, modified heat-dissipation sap flux sensors to monitor tamarisk water use (n = 20 trees) before, during and after defoliation by the saltcedar leaf beetle during the 2008 and 2009 growing seasons (May–October) in southeastern Utah. We incorporated a simple model that related mean stem sap flux density (Js) with atmospheric vapor pressure deficit (vpd) before the onset of defoliation in 2008. The model was used to calculate differences between predicted Js and Js measured throughout the two growing seasons. Episodic defoliation resulted in a 16% reduction in mean annual rates of Js in both 2008 and 2009, with decreases occurring only during the periods in which the trees were defoliated (about 6–8 weeks per growing season). In other words, rates of Js rebounded to values predicted by the model when the trees produced new leaves after defoliation. Sap flux data were scaled to stand water use by constructing a tamarisk-specific allometric equation to relate conducting sapwood area to stem diameter, and by measuring the size distribution of stems within the stand. Total water use in both years was 0.224 m, representing a reduction of about 0.04 m yr−1. Results showed that repeated defoliation/refoliation cycles did not result in a progressive decrease in either leaf production or water use over the duration of the study. This investigation improves ground-based estimates of tamarisk water use, and will support future efforts to characterize impacts of the beetle on basin-wide hydrologic processes.
• Jordan, F., Yoklic, M., Morino, K., Brown, P., Seaman, R., & Glenn, E. (2009). Consumptive water use and stomatal conductance of Atriplex lentiformis irrigated with industrial brine in a desert irrigation district. Agricultural and Forest Meteorology, 149(5), 899-912. doi:10.1016/j.agrformet.2008.11.010
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  The halophyte forage shrub, Atriplex lentiformis (quailbush), was irrigated with brine from a reverse-osmosis (RO) water treatment plant in an agricultural district in Marana, Arizona, in the Sonoran Desert, U.S. Small transplants were installed in large, outdoor drainage lysimeters and drip-irrigated with RO concentrate, on a schedule designed to deliver 1.5 times the reference evapotranspiration (ET0) on a daily basis, as determined by an on-site micrometeorological station. Water consumption was measured by a water-balance approach over an annual cycle and by measuring sap flow with heat-balance sensors over a 28-day period in August 2008. Over this annual cycle, biomass yield was 1.62 kg m-2 and the average water consumption during the growing season was 1.55 times ET0, similar to values for high-biomass crops such as alfalfa. The drainage fraction (water that exited lysimeters) was only 5% of the total input (irrigation plus precipitation) over the study. The Priestley-Taylor coefficient relating evapotranspiration (ET) to net radiation was 1.34, typical of values for freely transpiring crops under non-water-limiting conditions. Rates of transpiration measured by sap flow sensors were closely coupled to both solar radiation and atmospheric water demand on hourly and daily time steps. Stomatal conductance was high throughout the day and coupled to diurnal solar radiation. Although halophytes often exhibit low to moderate growth potential under natural conditions or in sub-optimal agricultural settings, the present results show that they have high growth potential when water and nutrients are not limiting. The high yield and consumptive water use by A. lentiformis makes it a good candidate for the reuse of industrial or agricultural brines in arid-zone irrigation districts. © 2008 Elsevier B.V. All rights reserved.
• Morino, K., Glenn, E. P., Didan, K., Erker, J., Hultine, K. R., Nagler, P. L., & Osterberg, J. (2009). Wide‐area estimates of saltcedar (Tamarix spp.) evapotranspiration on the lower Colorado River measured by heat balance and remote sensing methods. Ecohydrology, 2(1), 18-33. doi:10.1002/eco.35
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  In many places along the lower Colorado River, saltcedar (Tamarix spp) has replaced the native shrubs and trees, including arrowweed, mesquite, cottonwood and willows. Some have advocated that by removing saltcedar, we could save water and create environments more favourable to these native species. To test these assumptions we compared sap flux measurements of water used by native species in contrast to saltcedar, and compared soil salinity, ground water depth and soil moisture across a gradient of 200–1500 m from the river's edge on a floodplain terrace at Cibola National Wildlife Refuge (CNWR). We found that the fraction of land covered (fc) with vegetation in 2005–2007 was similar to that occupied by native vegetation in 1938 using satellite-derived estimates and reprocessed aerial photographs scaled to comparable spatial resolutions (3–4 m). We converted fc to estimates of leaf area index (LAI) through point sampling and destructive analyses (r2 = 0·82). Saltcedar LAI averaged 2·54 with an fc of 0·80, and reached a maximum of 3·7 with an fc of 0·95. The ranges in fc and LAI are similar to those reported for native vegetation elsewhere and from the 1938 photographs over the study site. On-site measurements of water use and soil and aquifer properties confirmed that although saltcedar grows in areas where salinity has increased much better than native shrubs and trees, rates of transpiration are similar. Annual water use over CNWR was about 1·15 m year−1. Copyright © 2008 John Wiley & Sons, Ltd.
• Murray, R. S., Nagler, P. L., Morino, K., & Glenn, E. P. (2009). An empirical algorithm for estimating agricultural and riparian evapotranspiration using MODIS enhanced vegetation index and ground measurements of ET. II. application to the lower Colorado river, U.S.. Remote Sensing, 1(Issue 4). doi:10.3390/rs1041125
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  Large quantities of water are consumed by irrigated crops and riparian vegetation in western U.S. irrigation districts. Remote sensing methods for estimating evaporative water losses by soil and vegetation (evapotranspiration, ET) over wide river stretches are needed to allocate water for agricultural and environmental needs. We used the Enhanced Vegetation Index (EVI) from MODIS sensors on the Terra satellite to scale ET over agricultural and riparian areas along the Lower Colorado River in the southwestern U.S., using a linear regression equation between ET of riparian plants and alfalfa measured on the ground, and meteorological and remote sensing data, with an error or uncertainty of about 20%. The algorithm was applied to irrigation districts and riparian areas from Lake Mead to the U.S./Mexico border. The results for agricultural crops were similar to results produced by crop coefficients developed for the irrigation districts along the river. However, riparian ET was only half as great as crop coefficient estimates set by expert opinion, equal to about 40% of reference crop evapotranspiration. Based on reported acreages in 2007, agricultural crops (146,473 ha) consumed 2.2 × 109 m3 yr--1 of water. All riparian shrubs and trees (47,014 ha) consumed 3.8 × 108 m3 yr-1, of which saltcedar, the dominant riparian shrub (25,044 ha), consumed 1.8 × 108 m3 yr-1, about 1% of the annual flow of the river. This method could supplement existing protocols for estimating ET by providing an estimate based on the actual state of the canopy as determined by frequent-return satellite data. © 2009 by the authors; licensee Molecular Diversity Preservation International, Basel, Switzerland.
• Glenn, E. P., Morino, K., Jordan, F., Carroll, K. C., Didan, K., Hultine, K. R., Jordan, F. L., Nagler, P. L., Sheader, L., & Waugh, J. (2008). Scaling sap flux measurements of grazed and ungrazed shrub communities with fine and coarse‐resolution remote sensing. Ecohydrology, 1(4), 316-329. doi:10.1002/eco.19
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  We measured transpiration by black greasewood (Sarcobatus vermiculatus) (SAVE) and fourwing saltbush (Atriplex canescens) (ATCA) over a nitrate-contaminated aquifer in Monument Valley, Arizona, on the Colorado Plateau. Heat balance sap flow sensors were used to measure transpiration by shrubs in 2006 and 2007 and results were scaled to larger landscape units and longer time scales using leaf area index (LAI), fractional vegetation cover, meteorological data, and the enhanced vegetation index (EVI) from MODIS sensors on the Terra satellite. Transpiration was high depending on leaf area (2·95–6·72 kg m−2 d−1) and was controlled by vapour pressure deficit (D) in the atmosphere. SAVE tended to have higher transpiration rates than ATCA and had a steeper response to D, but both exhibited midday depression of leaf conductance. Over most of the site, fractional vegetation cover (fc) and area-wide LAI were low (0·10 and 0·37, respectively) due to heavy grazing by cattle and sheep. However, a portion of the plume that had been protected from grazing for 10 years had fc = 0·75, LAI = 2·88. Transpiration rates on a ground-area basis varied with LAI, with midsummer daily values ranging from 1·44 mm d−1 (LAI = 0·36) to 13·1 mm d−1 (LAI = 2·88 mm) over the site, corresponding to projected annual values of 159–1447 mm year−1. Controlling grazing could, theoretically, slow or halt the movement of the contamination plume by allowing the shrub community to extract more water than is recharged in the aquifer. Copyright © 2008 John Wiley & Sons, Ltd. This article was published online on 26 September 2008. An error was subsequently identified. This notice is included in the online and print versions to indicate that both have been corrected (29 September 2008)
• Morino, K., Didan, K., Erker, J., Fleming, J. B., Glenn, E. P., Gloss, S., Jetton, A. J., Milliken, J., & Nagler, P. L. (2007). Evapotranspiration in a cottonwood (Populus fremontii) restoration plantation estimated by sap flow and remote sensing methods. Agricultural and Forest Meteorology, 144(1), 95-110. doi:10.1016/j.agrformet.2007.02.002
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  Abstract Native tree plantations have been proposed for the restoration of wildlife habitat in human-altered riparian corridors of western U.S. rivers. Evapotranspiration (ET) by riparian vegetation is an important, but poorly quantified, term in river water budgets. Native tree restoration plots will potentially increase ET. We used sap flow sensors and satellite imagery to estimate ET in a 8 ha, cottonwood ( Populus fremontii ) restoration plot on the Lower Colorado River. Biometric methods were used to scale leaf area to whole trees and stands of trees. This technique was used to validate our estimates of ET obtained by scaling from branch level to stand (or plot) level measurements of ET. Cottonwood trees used 6–10 mm day −1 of water during the peak of the growing season as determined by sap flow sensors, and annual rates scaled by time-series MODIS satellite imagery were approximately 1.2 m year −1 . Although irrigation was not quantified, the field had been flood irrigated at 2 week intervals during the 3 years prior to the study, receiving approximately 2 m year −1 of water. A frequency-domain electromagnetic induction survey of soil moisture content showed that the field was saturated (26–28% gravimetric water content) at the 90–150 cm soil depth under the field. Trees were apparently rooted into the saturated soil, and considerable saving of water could potentially be achieved by modifying the irrigation regime to take into account that cottonwoods are phreatophytes. The study showed that cottonwood ET can be monitored by remote sensing methods calibrated with ground measurements with an accuracy or uncertainty of 20–30% in western riparian corridors.

Proceedings Publications

• Nagler, P. L., Glenn, E. P., & Morino, K. (2012). Comparison of sap flux, moisture flux tower and MODIS Enhanced Vegetation Index methods for estimating riparian evapotranspiration. In Remote Sensing and Hydrology Symposium, 352.
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  Riparian evapotranspiration (ET) was measured on a salt cedar (Tamarix spp.) dominated river terrace on the Lower Colorado River from 2007 to 2009 using tissue-heat-balance sap flux sensors at six sites representing very dense, medium dense, and sparse stands of plants. Salt cedar ET varied markedly across sites, and sap flux sensors showed that plants were subject to various degrees of stress, detected as mid-day depression of transpiration and stomatal conductance. Sap flux results were scaled from the leaf level of measurement to the stand level by measuring plant-specific leaf area index and fractional ground cover at each site. Results were compared to Bowen ratio moisture tower data available for three of the sites. Sap flux sensors and flux tower results ranked the sites the same and had similar estimates of ET. A regression equation, relating measured ET of salt cedar and other riparian plants and crops on the Lower Colorado River to the Enhanced Vegetation Index from the MODIS sensor on the Terra satellite and reference crop ET measured at meteorological stations, was able to predict actual ET with an accuracy or uncertainty of about 20%, despite between-site differences for salt cedar. Peak summer salt cedar ET averaged about 6 mm d-1 across sites and methods of measurement. Copyright © 2012 IAHS Press.

Poster Presentations

• Hughes, M. K., Morino, K., & Brown, P. M. (2016, Spring). Cambial phenology, xylogenesis and tree-ring anatomy in pines in semi-arid southern Arizona. Ameridendro. Mendoza, Argentina: Tree-Ring Society.
• Meixner, T., Leavitt, S. W., & Morino, K. (2016, December). Water sources over time for a semi-arid river- Implications for water resources. AGU Fall Meeting. San Francisco, CA: American Geophysical Union.