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Featured submissions

May 2022

April 2022

March 2022

  • Rangelands, Volume 41 (2019), is now publicly available in the repository.

 

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  • Climate refugia for Pinus spp. in topographic and bioclimatic environments of the Madrean sky islands of México and the United States

    Haire, Sandra L.; Villarreal, Miguel L.; Cortés-Montaño, Citlali; Flesch, Aaron D.; Iniguez, José M.; Romo-Leon, Jose Raul; Sanderlin, Jamie S.; School of Natural Resources and the Environment and Desert Laboratory on Tumamoc Hill, University of Arizona (Springer Science and Business Media LLC, 2022-04-01)
    Climate refugia, or places where habitats are expected to remain relatively buffered from regional climate extremes, provide an important focus for science and conservation planning. Within high-priority, multi-jurisdictional landscapes like the Madrean sky islands of the United States and México, efforts to identify and manage climate refugia are hindered by the lack of high-quality and consistent transboundary datasets. To fill these data gaps, we assembled a bi-national field dataset (n = 1416) for five pine species (Pinus spp.) and used generalized boosted regression to model pine habitats in relation to topographic variability as a basis for identifying potential microrefugia at local scales in the context of current species’ distribution patterns. We developed additional models to quantify climatic refugial attributes using coarse scale bioclimatic variables and finer scale seasonal remote sensing indices. Terrain metrics including ruggedness, slope position, and aspect defined microrefugia for pines within elevation ranges preferred by each species. Response to bioclimatic variables indicated that small shifts in climate were important to some species (e.g., P. chihuahuana, P. strobiformis), but others exhibited a broader tolerance (e.g., P. arizonica). Response to seasonal climate was particularly important in modeling microrefugia for species with open canopy structure and where regular fires occur (e.g., P. engelmannii and P. chihuahuana). Hotspots of microrefugia differed among species and were either limited to northern islands or occurred across central or southern latitudes. Mapping and validation of refugia and their ecological functions are necessary steps in developing regional conservation strategies that cross jurisdictional boundaries. A salient application will be incorporation of climate refugia in management of fire to restore and maintain pine ecology. Una versión en español de este artículo está disponible como descarga.
  • Where did the Arizona-Plano Go? Protracted Thinning Via Upper- to Lower-Crustal Processes

    Jepson, G.; Carrapa, B.; George, S.W.M.; Reeher, L.J.; Kapp, P.A.; Davis, G.H.; Thomson, S.N.; Amadori, C.; Clinkscales, C.; Jones, S., I; et al. (John Wiley and Sons Inc, 2022)
    Mesozoic-Cenozoic subduction of the Farallon slab beneath North America generated a regionally extensive orogenic plateau in the southwestern US during the latest Cretaceous, similar to the modern Central Andean Plateau. In Nevada and southern Arizona, estimates from whole-rock geochemistry suggest crustal thicknesses reached ∼60–55 km by the Late Cretaceous. Modern crustal thicknesses are ∼28 km, requiring significant Cenozoic crustal thinning. Here, we compare detailed low-temperature thermochronology from the Catalina metamorphic core complex (MCC) to whole rock Sr/Y crustal thickness estimates across southern Arizona. We identify three periods of cooling. A minor cooling phase occurred prior to ∼40 Ma with limited evidence of denudation and ∼10 km of crustal thinning. Major cooling occurred during detachment faulting and MCC formation at 26–19 Ma, corresponding to ∼8 km of denudation and ∼8 km of crustal thinning. Finally, we document a cooling phase at 17–11 Ma related to Basin and Range extension that corresponds with ∼5 km of denudation and ∼9 km of crustal thinning. During the MCC and Basin and Range extension events, the amount of denudation recorded by low-temperature thermochronology can be explained by corresponding decreases in the crustal thickness. However, the relatively limited exhumation prior to detachment faulting at ∼26 Ma recorded by thermochronology is insufficient to explain the magnitude of crustal thinning (∼10 km) observed in the whole rock crustal thickness record. Therefore, we suggest that crustal thinning of the Arizona-plano was facilitated via ductile mid- to lower-crustal flow, and limited upper-crustal extension at 50–30 Ma prior to detachment faulting and Basin and Range extension. © 2022. American Geophysical Union. All Rights Reserved.
  • Coupling of Tree Growth and Photosynthetic Carbon Uptake Across Six North American Forests

    Teets, A.; Moore, D.J.P.; Alexander, M.R.; Blanken, P.D.; Bohrer, G.; Burns, S.P.; Carbone, M.S.; Ducey, M.J.; Fraver, S.; Gough, C.M.; et al. (John Wiley and Sons Inc, 2022)
    Linking biometric measurements of stand-level biomass growth to tower-based measurements of carbon uptake—gross primary productivity and net ecosystem productivity—has been the focus of numerous ecosystem-level studies aimed to better understand the factors regulating carbon allocation to slow-turnover wood biomass pools. However, few of these studies have investigated the importance of previous year uptake to growth. We tested the relationship between wood biomass increment (WBI) and different temporal periods of carbon uptake from the current and previous years to investigate the potential lagged allocation of fixed carbon to growth among six mature, temperate forests. We found WBI was strongly correlated to carbon uptake across space (i.e., long-term averages at the different sites) but on annual timescales, WBI was much less related to carbon uptake, suggesting a temporal mismatch between C fixation and allocation to biomass. We detected lags in allocation of the previous year's carbon uptake to WBI at three of the six sites. Sites with higher annual WBI had overall stronger correlations to carbon uptake, with the strongest correlations to carbon uptake from the previous year. Only one site had WBI with strong positive relationships to current year uptake and not the previous year. Forests with low rates of WBI demonstrated weak correlations to carbon uptake from the previous year and stronger relationships to current year climate conditions. Our work shows an important, but not universal, role of lagged allocation of the previous year's carbon uptake to growth in temperate forests. © 2022. American Geophysical Union. All Rights Reserved.
  • Energy transfer processes in hyperfluorescent organic light-emitting diodes

    Cho, E.; Hong, M.; Yang, Y.S.; Cho, Y.J.; Coropceanu, V.; Brédas, J.-L.; Department of Chemistry and Biochemistry, The University of Arizona (Royal Society of Chemistry, 2022)
    Hyperfluorescent organic light-emitting diodes (OLEDs) are based on a combination of molecules displaying thermally activated delayed fluorescence (TADF) and of fluorescent emitters embedded into a host matrix; excitons formed on the TADF molecules are expected to transfer to the fluorescent emitters. As a result, device performance strongly depends on the efficiency of the relevant energy transfer processes. Here, we investigate the morphology, excited-state properties, and energy-transfer processes in a ternary TBRb:4CzIPN:mCBP blend by using complementary molecular dynamics simulations and density functional theory calculations. The results indicate that the rate constants for singlet exciton energy transfer from 4CzIPN (TADF) molecules to TBRb fluorescent emitters are about three orders of magnitude larger than both the intersystem crossing (ISC) and radiative decay rate constants of 4CzIPN; thus, the vast majority of the singlet 4CzIPN excitons can efficiently transfer to the emitters. In contrast, the transfer of triplet excitons from 4CzIPN to the emitters is limited due to a fast reverse ISC (RISC) transition. Also, it is found that singlet and triplet energy transfer from mCBP to 4CzIPN and TBRb is very efficient. As a result of quasi resonance between the emissive first excited state and the second triplet state of TBRb, not all triplet excitons that reach TBRb are lost since part of them can convert into singlet excitons via a RISC process. © 2022 The Royal Society of Chemistry
  • Ferrofettelite, [Ag6As2S7][Ag10FeAs2S8], a new sulfosalt from the Glasberg quarry, Odenwald, Germany

    Bindi, L.; Downs, R.T.; Department of Geosciences, University of Arizona (Cambridge University Press, 2022)
    Ferrofettelite, ideally [Ag6As2S7][Ag10FeAs2S8], is a new mineral (IMA No. 2021-094) from the Glasberg quarry, Nieder-Beerbach, Odenwald, south-western Germany. It occurs as anhedral to subhedral flakes and grains up to 80 μm, associated with proustite and xanthoconite, on arsenolite, calcite and prehnite. Ferrofettelite is opaque with a metallic luster and possesses a dark reddish-grey streak. It is brittle with an uneven fracture; the Vickers microhardness (VHN20) is 122 kg/mm2(range 111–131). The calculated density is 5.74 g/cm3(on the basis of the empirical formula). In plane-polarized reflected light, ferrofettelite is greyish white. Between crossed polars it is weakly anisotropic with red internal reflections. Electron-microprobe analyses give the chemical formula Ag16.04(Fe0.55Hg0.40Cu0.02)Σ0.97(As3.94Sb0.03)Σ3.97S15.02 on the basis of total atoms = 36. Ferrofettelite is monoclinic, space group C2, with a = 26.011(2), b = 15.048(1), c = 15.513(1) Å, β = 90.40(1)°, V = 6071.9(7) Å3, and Z = 8. The six strongest Bragg peaks in the X-ray powder diffraction pattern (d[Å], I[%], hkl) are: (3.18, 50, -801), (3.104, 100, 005), (3.004, 60, -802), (2.755, 40, -443), (2.501, 30, -444) and (1.880, 30, 1240). The crystal structure can be described as the alternation of two kinds of layers along the c-axis: layer A with general composition [Ag6As2S7]2-and layer B with a general composition of [Ag10FeAs2S8]2+. In the structure, the Ag atoms adopt various coordinations extending from quasi linear to quasi tetrahedral, the AsS3 groups form pyramids as are typically observed in sulfosalts, and mixed (Fe,Hg) links two sulfur atoms in a linear coordination. Ferrofettelite is the first reported inorganic phase showing a linear coordination for Fe2+. The high-temperature behavior of ferrofettelite was studied up to 410 K and compared to that of fettelite. © 2022 Cambridge University Press. All rights reserved.

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