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  • 1
    In: Journal of Geophysical Research: Biogeosciences, American Geophysical Union (AGU), Vol. 126, No. 4 ( 2021-04)
    Abstract: Tundra fires occur preferentially in more productive areas, and tundra vegetation is highly resilient to burning Postfire greening occurs in two phases. Phase one occurs in all plant communities immediately after a fire. Phase two occurs where and when postfire shrub expansion is facilitated by permafrost thaw The tussock and shrub fire regimes operating in the Noatak may become ecological attractor states elsewhere as tundra fires expand northward
    Type of Medium: Online Resource
    ISSN: 2169-8953 , 2169-8961
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2021
    detail.hit.zdb_id: 3094167-2
    detail.hit.zdb_id: 2220777-6
    SSG: 16,13
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  • 2
    In: The Holocene, SAGE Publications, Vol. 29, No. 11 ( 2019-11), p. 1817-1830
    Abstract: In north-western North America, the so-called divergence problem (DP) is expressed in tree ring width (RW) as an unstable temperature signal in recent decades. Maximum latewood density (MXD), from the same region, shows minimal evidence of DP. While MXD is a superior proxy for summer temperatures, there are very few long MXD records from North America. Latewood blue intensity (LWB) measures similar wood properties as MXD, expresses a similar climate response, is much cheaper to generate and thereby could provide the means to profoundly expand the extant network of temperature sensitive tree-ring (TR) chronologies in North America. In this study, LWB is measured from 17 white spruce sites ( Picea glauca) in south-western Yukon to test whether LWB is immune to the temporal calibration instabilities observed in RW. A number of detrending methodologies are examined. The strongest calibration results for both RW and LWB are consistently returned using age-dependent spline (ADS) detrending within the signal-free (SF) framework. RW data calibrate best with June–July maximum temperatures (Tmax), explaining up to 28% variance, but all models fail validation and residual analysis. In comparison, LWB calibrates strongly (explaining 43–51% of May–August Tmax) and validates well. The reconstruction extends to 1337 CE, but uncertainties increase substantially before the early 17th century because of low replication. RW-, MXD- and LWB-based summer temperature reconstructions from the Gulf of Alaska, the Wrangell Mountains and Northern Alaska display good agreement at multi-decadal and higher frequencies, but the Yukon LWB reconstruction appears potentially limited in its expression of centennial-scale variation. While LWB improves dendroclimatic calibration, future work must focus on suitably preserved sub-fossil material to increase replication prior to 1650 CE.
    Type of Medium: Online Resource
    ISSN: 0959-6836 , 1477-0911
    RVK:
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2019
    detail.hit.zdb_id: 2027956-5
    SSG: 14
    SSG: 3,4
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  • 3
    In: Reviews of Geophysics, American Geophysical Union (AGU), Vol. 57, No. 4 ( 2019-12), p. 1224-1264
    Abstract: We review the merits and state of the art of tree‐ring wood microdensitometry and its associated analytical challenges We show that systematic level offsets in mean wood density from different techniques and laboratories require correction Measurement resolution—notoriously difficult to control—is identified as the major challenge for future research applications
    Type of Medium: Online Resource
    ISSN: 8755-1209 , 1944-9208
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2019
    detail.hit.zdb_id: 2035391-1
    detail.hit.zdb_id: 209852-0
    detail.hit.zdb_id: 209853-2
    SSG: 16,13
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  • 4
    In: Nature Climate Change, Springer Science and Business Media LLC, Vol. 5, No. 6 ( 2015-6), p. 579-583
    Type of Medium: Online Resource
    ISSN: 1758-678X , 1758-6798
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2015
    detail.hit.zdb_id: 2603450-5
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  • 5
    In: Geophysical Research Letters, American Geophysical Union (AGU), Vol. 48, No. 16 ( 2021-08-28)
    Abstract: Optical blue intensity techniques are used to reevaluate Siberian larch cores, resulting in an eight‐century temperature reconstruction Central Asia warmed rapidly over the past few decades; future projections exceed both observed and reconstructed temperatures Large tropical volcanic eruptions resulted in about a 0.6°C cooling at 1‐year post event with subsequent cooling for up to 5 years
    Type of Medium: Online Resource
    ISSN: 0094-8276 , 1944-8007
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2021
    detail.hit.zdb_id: 2021599-X
    detail.hit.zdb_id: 7403-2
    SSG: 16,13
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  • 6
    Online Resource
    Online Resource
    Springer Science and Business Media LLC ; 2019
    In:  Nature Communications Vol. 10, No. 1 ( 2019-02-14)
    In: Nature Communications, Springer Science and Business Media LLC, Vol. 10, No. 1 ( 2019-02-14)
    Abstract: Historical and future trends in net primary productivity (NPP) and its sensitivity to global change are largely unknown because of the lack of long-term, high-resolution data. Here we test whether annually resolved tree-ring stable carbon (δ 13 C) and oxygen (δ 18 O) isotopes can be used as proxies for reconstructing past NPP. Stable isotope chronologies from four sites within three distinct hydroclimatic environments in the eastern United States (US) were compared in time and space against satellite-derived NPP products, including the long-term Global Inventory Modeling and Mapping Studies (GIMMS3g) NPP (1982–2011), the newest high-resolution Landsat NPP (1986–2015), and the Moderate Resolution Imaging Spectroradiometer (MODIS, 2001–2015) NPP. We show that tree-ring isotopes, in particular δ 18 O, correlate strongly with satellite NPP estimates at both local and large geographical scales in the eastern US. These findings represent an important breakthrough for estimating interannual variability and long-term changes in terrestrial productivity at the biome scale.
    Type of Medium: Online Resource
    ISSN: 2041-1723
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2019
    detail.hit.zdb_id: 2553671-0
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  • 7
    In: Ecology and Evolution, Wiley, Vol. 7, No. 16 ( 2017-08), p. 6334-6345
    Abstract: In temperate climates, tree growth dormancy usually ensures the annual nature of tree rings, but in tropical environments, determination of annual periodicity can be more complex. The purposes of the work are as follows: (1) to generate a reliable tree‐ring width chronology for Prioria copaifera Griseb. (Leguminoceae), a tropical tree species dwelling in the Atrato River floodplains, Colombia; (2) to assess the climate signal recorded by the tree‐ring records; and (3) to validate the annual periodicity of the tree rings using independent methods. We used standard dendrochronological procedures to generate the P. copaifera tree‐ring chronology. We used Pearson correlations to evaluate the relationship of the chronology with the meteorological records, climate regional indices, and gridded precipitation/sea surface temperature products. We also evaluated 24 high‐precision 14 C measurements spread over a range of preselected tree rings, with assigned calendar years by dendrochronological techniques, before and after the bomb spike in order to validate the annual nature of the tree rings. The tree‐ring width chronology was statistically reliable, and it correlated significantly with local records of annual and October–December ( OND ) streamflow and precipitation across the upper river watershed (positive), and OND temperature (negative). It was also significantly related to the Oceanic Niño Index, Pacific Decadal Oscillation, and the Southern Oscillation Index, as well as sea surface temperatures over the Caribbean and the Pacific region. However, 14 C high‐precision measurements over the tree rings demonstrated offsets of up to 40 years that indicate that P. copaifera can produce more than one ring in certain years. Results derived from the strongest climate–growth relationship during the most recent years of the record suggest that the climatic signal reported may be due to the presence of annual rings in some of those trees in recent years. Our study alerts about the risk of applying dendrochronology in species with challenging anatomical features defining tree rings, commonly found in the tropics, without an independent validation of annual periodicity of tree rings. High‐precision 14 C measurements in multiple trees are a useful method to validate the identification of annual tree rings.
    Type of Medium: Online Resource
    ISSN: 2045-7758 , 2045-7758
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2017
    detail.hit.zdb_id: 2635675-2
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  • 8
    Online Resource
    Online Resource
    Oxford University Press (OUP) ; 2020
    In:  Tree Physiology Vol. 40, No. 5 ( 2020-05-11), p. 605-620
    In: Tree Physiology, Oxford University Press (OUP), Vol. 40, No. 5 ( 2020-05-11), p. 605-620
    Abstract: Increasing dryness challenges trees’ ability to maintain water transport to the leaves. Most plant hydraulics models use a static xylem response to water stress. Yet, in reality, lower soil moisture and warmer temperatures during growing seasons feed back onto xylem development. In turn, adjustments to water stress in the newly built xylem influence future physiological responses to droughts. In this study, we investigate the annual variation of anatomical traits in branch xylem in response to different soil and atmospheric moisture conditions and tree stress levels, as indicated by seasonal predawn leaf water potential (ΨL,pd). We used a 6-year field experiment in southwestern USA with three soil water treatments applied to Pinus edulis Engelm trees—ambient, drought (45% rain reduction) and irrigation (15–35% annual water addition). All trees were also subject to a natural 1-year acute drought (soil and atmospheric) that occurred during the experiment. The irrigated trees showed only moderate changes in anatomy-derived hydraulic traits compared with the ambient trees, suggesting a generally stable, well-balanced xylem structure under unstressed conditions. The artificial prolonged soil drought increased hydraulic efficiency but lowered xylem construction costs and decreased tracheid implosion safety ((t/b)2), suggesting that annual adjustments of xylem structure follow a safety–efficiency trade-off. The acute drought plunged hydraulic efficiency across all treatments. The combination of acute and prolonged drought resulted in vulnerable and inefficient new xylem, disrupting the stability of the anatomical trade-off observed in the rest of the years. The xylem hydraulic traits showed no consistent direct link to ΨL,pd. In the future, changes in seasonality of soil and atmospheric moisture are likely to have a critical impact on the ability of P. edulis to acclimate its xylem to warmer climate. Furthermore, the increasing frequency of acute droughts might reduce hydraulic resilience of P. edulis by repeatedly creating vulnerable and less efficient anatomical structure.
    Type of Medium: Online Resource
    ISSN: 1758-4469
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2020
    detail.hit.zdb_id: 1473475-8
    SSG: 12
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  • 9
    Online Resource
    Online Resource
    Inter-Research Science Center ; 2012
    In:  Climate Research Vol. 55, No. 2 ( 2012-11-29), p. 119-134
    In: Climate Research, Inter-Research Science Center, Vol. 55, No. 2 ( 2012-11-29), p. 119-134
    Type of Medium: Online Resource
    ISSN: 0936-577X , 1616-1572
    Language: English
    Publisher: Inter-Research Science Center
    Publication Date: 2012
    detail.hit.zdb_id: 2021517-4
    SSG: 14
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  • 10
    In: Ecology and Evolution, Wiley, Vol. 8, No. 3 ( 2018-02), p. 1655-1672
    Abstract: In the southwestern USA , recent large‐scale die‐offs of conifers raise the question of their resilience and mortality under droughts. To date, little is known about the interannual structural response to droughts. We hypothesized that piñon pines ( Pinus edulis ) respond to drought by reducing the drop of leaf water potential in branches from year to year through needle morphological adjustments. We tested our hypothesis using a 7‐year experiment in central New Mexico with three watering treatments (irrigated, normal, and rain exclusion). We analyzed how variation in “evaporative structure” (needle length, stomatal diameter, stomatal density, stomatal conductance) responded to watering treatment and interannual climate variability. We further analyzed annual functional adjustments by comparing yearly addition of needle area ( LA ) with yearly addition of sapwood area ( SA ) and distance to tip ( d ), defining the yearly ratios SA : LA and SA : LA / d . Needle length ( l ) increased with increasing winter and monsoon water supply, and showed more interannual variability when the soil was drier. Stomatal density increased with dryness, while stomatal diameter was reduced. As a result, anatomical maximal stomatal conductance was relatively invariant across treatments. SA : LA and SA : LA / d showed significant differences across treatments and contrary to our expectation were lower with reduced water input. Within average precipitation ranges, the response of these ratios to soil moisture was similar across treatments. However, when extreme soil drought was combined with high VPD , needle length, SA : LA and SA : LA / d became highly nonlinear, emphasizing the existence of a response threshold of combined high VPD and dry soil conditions. In new branch tissues, the response of annual functional ratios to water stress was immediate (same year) and does not attempt to reduce the drop of water potential. We suggest that unfavorable evaporative structural response to drought is compensated by dynamic stomatal control to maximize photosynthesis rates.
    Type of Medium: Online Resource
    ISSN: 2045-7758 , 2045-7758
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2018
    detail.hit.zdb_id: 2635675-2
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