A millennium-length reconstruction of Bear River stream flow, Utah

The Bear River contributes more water to the eastern Great Basin than any other river system. It is also the most significant source of water for the burgeoning Wasatch Front metropolitan area in northern Utah. Despite its importance for water resources for the region’s agricultural, urban, and wildlife needs, our understanding of the variability of Bear River’s stream flow derives entirely from the short instrumental record (1943–2010). Here we present a 1200-year calibrated and verified tree-ring reconstruction of stream flow for the Bear River that explains 67% of the variance of the instrumental record over the period from 1943 to 2010. Furthermore, we developed this reconstruction from a species that is not typically used for dendroclimatology, Utah juniper (Juniperus osteosperma). We identify highly significant periodicity in our reconstruction at quasi-decadal (7–8 year), multi-decadal (30 year), and centennial (>50 years) scales. The latter half of the 20th century was found to be the 2nd wettest (∼40-year) period of the past 1200 years, while the first half of the 20th century marked the 4th driest period. The most severe period of reduced stream flow occurred during the Medieval Warm Period (ca. mid-1200s CE) and persisted for ∼70 years. Upper-level circulation anomalies suggest that atmospheric teleconnections originating in the western tropical Pacific are responsible for the delivery of precipitation to the Bear River watershed during the October–December (OND) season of the previous year. The Bear River flow was compared to recent reconstructions of the other tributaries to the Great Salt Lake (GSL) and the GSL level. Implications for water management could be drawn from the observation that the latter half of the 20th century was the 2nd wettest in 1200 years, and that management for future water supply should take into account the stream flow variability over the past millennium

Morphological and genetic variation among Sphaeralcea Species in a high desert environment

The herbaceous perennial species in the genus Sphaeralcea have desirable drought tolerance and aesthetics with potential for low-water use landscapes in the Intermountain West. However, taxonomy of these species is ambiguous, which leads to decreased consumer confidence in the native plant nursery industry. The goal of this study was to test and clarify morphological and genetic differentiation among four putative Sphaeralcea species. Morphological characteristics of the type specimens were used as species references in canonical variate analysis to generate a classification model. This model was then used to assign putative species names to herbarium voucher specimens and to field-collected voucher specimens to clarify genetic variation among species. Field specimens were also classified using Bayesian cluster analyses of amplified fragment length polymorphism (AFLP) genotypes. Sphaeralcea coccinea (Nutt.) Rydb. and S. grossulariifolia (Hook. & Arn.) Rydb. formed a composite group morphologically and genetically distinct from the S. munroana (Douglas) Spach and S. parvifolia A. Nelson composite group. Each composite group displayed genetic isolation by geographic distance. Also, morphological traits of S. munroana and S. parvifolia correlated to geographic distance. Taken together these results suggest that our samples represent two sympatric yet reproductively isolated groups. Distinguishing between these two Sphaeralcea composite groups can create greater consumer confidence in plant material developed for use in Intermountain West low-water landscaping

Drought responses of six ornamental herbaceous perennials

Although low water use landscaping is becoming common in arid regions, little is known about drought tolerance and drought responses of many ornamental plants, especially herbaceous perennials. Drought responses were assessed for six herbaceous ornamental landscape perennials in a 38 l pot-in-pot system in northern Utah over a 2-year period. The first year was an establishment period. During the second year, drought responses were evaluated for established Echinacea purpurea (L.) Moench, Gaillardia aristata Pursh, Lavandula angustifolia P. Mill., Leucanthemum × superbum (J.W. Ingram) Berg. ex Kent, ‘Alaska’, Penstemon barbatus Roth var. praecox nanus rondo, and Penstemon × mexicali Mitch. ‘Red Rocks’. Plants were irrigated at frequencies of 1 (control), 2, or 4 weeks between June and September, simulating well-watered conditions, moderate drought, or severe drought. Osmotic potential (Ψs), gas exchange, visual quality, leaf area, and dry weight were assessed. In a confined root zone, P. barbatus showed the greatest tolerance to all levels of drought, avoiding desiccation by increasing root:shoot ratio and decreasing stomatal conductance as water became limiting. L. angustifolia and P. × mexicali showed tolerance to moderate drought conditions, but died after exposure to the first episode of severe drought. Neither G. aristata nor L. superbum were able to regulate shoot water loss effectively. Instead, both species displayed drought avoidance mechanisms, dying back when water was limiting and showing new growth after they were watered. Compared to control plants, G. aristata shoot dry weight was reduced by 50% and 84%, and L. superbum shoot dry weight was reduced by 47% and 99% for the 2- and 4-week irrigation intervals, respectively. Root dry weights were affected similarly for both species. E. purpurea exhibited poor visual quality at all irrigation intervals, in particular wilting severely in both drought treatments, but regaining turgor when watered again. P. barbatus is recommended for ornamental landscapes that receive little or no supplemental irrigation, while E. purpurea is not recommended for low water landscapes because of low visual quality under even mild drought.

Anisohydric water use behavior links growing season evaporative demand to ring-width increment in conifers from summer-dry environments

Key message: Compared to isohydric Pinaceae, anisohydric Cupressaceae exhibited: (1) a threefold larger hydroscape area; (2) growth at lower pre-dawn water potentials that extended longer into the growing season; and (3) stronger coupling of growth to growing season atmospheric moisture demand in summer-dry environments. Abstract: Conifers in the Pinaceae and Cupressaceae from dry environments have been shown to broadly differ in their stomatal sensitivity to soil drying that result in isohydric versus anisohydric water use behavior, respectively. Here, we first employ a series of drought experiments and field observations to confirm the degree of isohydric versus anisohydric water use behavior in species of these two families that are representative of the Interior West of the United States. We then use experimental soil drying to demonstrate how growth of anisohydric Juniperus osteosperma was more closely tied to pre-dawn water potentials than isohydric Pinus monophylla. Finally, we confirm that measured leaf gas-exchange and growth responses to drying hold real-world consequences for conifers from the Interior West. More specifically, across the past ~ 100 years of climate variation, pairwise comparisons of annual ring-width increment responses indicate that growth of Cupressaceae species (J. osteosperma and J. scopulorum) was more strongly coupled to growing season evaporative demand than co-occurring Pinaceae species (Pinus monophylla, P. edulis, P. flexilis, P. longaeva, P. ponderosa, and Pseudotsuga menziesii). Overall, these experimental and observational results suggest that an a priori distinction based on family and associated hydric water use behavior should lead to more accurate and mechanistically correct dendrochronological reconstructions of growing season evaporative demand (i.e., Cupressaceae) versus antecedent precipitation (i.e., Pinaceae) in summer-dry environments. Moreover, these differences in growth sensitivity to evaporative demand among these groups suggest that incorporating hydric water use behavior into models of forest responses to global warming can provide more accurate projections of future forest composition and functioning