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Open AccessReview
A Review of Bolt Tightening Force Measurement and Loosening Detection
Sensors 2020, 20(11), 3165; https://doi.org/10.3390/s20113165 (registering DOI) - 02 Jun 2020
Abstract
Pre-stressed bolted joints are widely used in civil structures and industries. The tightening force of a bolt is crucial to the reliability of the joint connection. Loosening or over-tightening of a bolt may lead to connectors slipping or bolt strength failure, which are [...] Read more.
Pre-stressed bolted joints are widely used in civil structures and industries. The tightening force of a bolt is crucial to the reliability of the joint connection. Loosening or over-tightening of a bolt may lead to connectors slipping or bolt strength failure, which are both harmful to the main structure. In most practical cases it is extremely difficult, even impossible, to install the bolts to ensure there is a precise tension force during the construction phase. Furthermore, it is inevitable that the bolts will loosen due to long-term usage under high stress. The identification of bolt tension is therefore of great significance for monitoring the health of existing structures. This paper reviews state-of-the-art research on bolt tightening force measurement and loosening detection, including fundamental theories, algorithms, experimental set-ups, and practical applications. In general, methods based on the acoustoelastic principle are capable of calculating the value of bolt axial stress if both the time of incident wave and reflected wave can be clearly recognized. The relevant commercial instrument has been developed and its algorithm will be briefly introduced. Methods based on contact dynamic phenomena such as wave energy attenuation, high-order harmonics, sidebands, and impedance, are able to correlate interface stiffness and the clamping force of bolted joints with respective dynamic indicators. Therefore, they are able to detect or quantify bolt tightness. The related technologies will be reviewed in detail. Potential challenges and research trends will also be discussed. Full article
(This article belongs to the Section Fault Diagnosis & Sensors)
Open AccessArticle
Enantiodivergent Aldol Condensation in the Presence of Aziridine/Acid/Water Systems
Symmetry 2020, 12(6), 930; https://doi.org/10.3390/sym12060930 (registering DOI) - 02 Jun 2020
Abstract
A series of novel chiral imines was synthesized from corresponding aldehydes and 1-(2-aminoalkyl)aziridines with good chemical yields. Such imines were tested as catalysts in the direct asymmetric aldol reaction between aromatic aldehydes and acetone/cyclohexanone in the presence of catalytic amounts of water and [...] Read more.
A series of novel chiral imines was synthesized from corresponding aldehydes and 1-(2-aminoalkyl)aziridines with good chemical yields. Such imines were tested as catalysts in the direct asymmetric aldol reaction between aromatic aldehydes and acetone/cyclohexanone in the presence of catalytic amounts of water and an acidic additive. The corresponding aldol products were formed in excellent yields and with very high enantioselectivities (98% and 99% ee, respectively). Full article
(This article belongs to the Special Issue Asymmetry and Symmetry in Organic Chemistry)
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Open AccessArticle
XPS Studies of the Initial Oxidation of Polycrystalline Rh Surface
Catalysts 2020, 10(6), 617; https://doi.org/10.3390/catal10060617 - 02 Jun 2020
Abstract
Increased interest in the oxidation process of polycrystalline rhodium, observed in recent years, is the result of its application in exhaust catalytic converters. However, most studies have involved sample surfaces with low Miller indices. In our research, we investigated polycrystalline rhodium foil containing [...] Read more.
Increased interest in the oxidation process of polycrystalline rhodium, observed in recent years, is the result of its application in exhaust catalytic converters. However, most studies have involved sample surfaces with low Miller indices. In our research, we investigated polycrystalline rhodium foil containing crystallographically different, highly stepped, µm-sized crystallites. These crystallites were exposed to identical oxidizing conditions. To determine crystallographic orientation, the electron backscattering diffraction (EBSD) method was used. To investigate the initial stages of oxidation on the individual crystallites of Rh, X-ray photoelectron spectroscopy (XPS) studies were performed. The results obtained for the individual crystallites were compared and analyzed using chemical state quantification of XPS data and multivariate statistical analysis (MVA). Full article
(This article belongs to the Special Issue Surface Chemistry in Catalysis)
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Open AccessFeature PaperArticle
Metric f-Contact Manifolds Satisfying the (κ, μ)-Nullity Condition
Mathematics 2020, 8(6), 891; https://doi.org/10.3390/math8060891 - 02 Jun 2020
Abstract
We prove that if the f-sectional curvature at any point of a (2n+s)-dimensional metric f-contact manifold satisfying the (κ,μ) nullity condition with n>1 is independent of the f-section [...] Read more.
We prove that if the f-sectional curvature at any point of a ( 2 n + s ) -dimensional metric f-contact manifold satisfying the ( κ , μ ) nullity condition with n > 1 is independent of the f-section at the point, then it is constant on the manifold. Moreover, we also prove that a non-normal metric f-contact manifold satisfying the ( κ , μ ) nullity condition is of constant f-sectional curvature if and only if μ = κ + 1 and we give an explicit expression for the curvature tensor field in such a case. Finally, we present some examples. Full article
(This article belongs to the Special Issue Sasakian Space)
Open AccessArticle
Ubiquinol-10 Intake Is Effective in Relieving Mild Fatigue in Healthy Individuals
Nutrients 2020, 12(6), 1640; https://doi.org/10.3390/nu12061640 - 02 Jun 2020
Abstract
Our double-blind, placebo-controlled study evaluated effects of ubiquinol, the reduced form of coenzyme Q10, on mild fatigue in healthy individuals experiencing fatigue in daily life that had continued for more than 1 and less than 6 months. The participants received 100-mg/day [...] Read more.
Our double-blind, placebo-controlled study evaluated effects of ubiquinol, the reduced form of coenzyme Q10, on mild fatigue in healthy individuals experiencing fatigue in daily life that had continued for more than 1 and less than 6 months. The participants received 100-mg/day (Ubq100; age 44.0 ± 9.8 years; 14 females and 6 males) or 150-mg/day ubiquinol (Ubq150; age 40.4 ± 11.8 years; 14 females and 8 males) or placebo (Plc; age 41.3 ± 13.4 years; 13 females and 7 males) daily for 12 weeks. Measurements of subjective and objective fatigue were conducted by using questionnaires-based fatigue scales/visual analogue scales and autonomic nerve function/biological oxidation index, respectively, prior to the first dosing and every 4 weeks thereafter. Serum ubiquinol level increased three- to four-fold after 4 weeks and remained significantly higher than that after Plc administration throughout the intake period. Although a higher blood level of ubiquinol was observed with Ubq150 than with Ubq100, the difference was not statistically significant. In both Ubq100 and Ubq150 groups, subjective levels of fatigue sensation and sleepiness after cognitive tasks, which consisted of the modified Advanced Trail Making Test, the modified Stroop Color-Word Test, and the Digit Symbol Substitution Test, improved significantly compared with those in the placebo group, suggesting an anti-fatigue effect. The Ubq150 group demonstrated significant improvement compared with the Plc group regarding subjective level of relaxation after task, sleepiness before and after task, motivation for task, and serum level of oxidative stress. Correlation analysis between blood level of ubiquinol and each evaluated effect suggested a positive relationship with relaxation after task, motivation for cognitive task, and parasympathetic activity. The results of the study suggest that ubiquinol intake relieves mild fatigue in healthy individuals. Full article
(This article belongs to the Section Clinical Nutrition)
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Open AccessReview
The Long and Short of It: The Emerging Roles of Non-Coding RNA in Small Extracellular Vesicles
Cancers 2020, 12(6), 1445; https://doi.org/10.3390/cancers12061445 - 02 Jun 2020
Abstract
Small extracellular vesicles (EVs) play a significant role in intercellular communication through their non-coding RNA (ncRNA) cargo. While the initial examination of EV cargo identified both mRNA and miRNA, later studies revealed a wealth of other types of EV-related non-randomly packed ncRNAs, including [...] Read more.
Small extracellular vesicles (EVs) play a significant role in intercellular communication through their non-coding RNA (ncRNA) cargo. While the initial examination of EV cargo identified both mRNA and miRNA, later studies revealed a wealth of other types of EV-related non-randomly packed ncRNAs, including tRNA and tRNA fragments, Y RNA, piRNA, rRNA, and lncRNA. A number of potential roles for these ncRNA species were suggested, with strong evidence provided in some cases, whereas the role for other ncRNA is more speculative. For example, long non-coding RNA might be used as a potential diagnostic tool but might also mediate resistance to certain cancer-specific chemotherapy agents. piRNAs, on the other hand, have a significant role in genome integrity, however, no role has yet been defined for the piRNAs found in EVs. While our knowledgebase for the function of ncRNA-containing EVs is still modest, the potential role that these EV-ensconced ncRNA might play is promising. This review summarizes the ncRNA content of EVs and describes the function where known, or the potential utility of EVs that harbor specific types of ncRNA. Full article
Open AccessArticle
Quantitative Determination Procedures for Regional Extreme Drought Conditions: Application to Historical Drought Events in South Korea
Atmosphere 2020, 11(6), 581; https://doi.org/10.3390/atmos11060581 - 02 Jun 2020
Abstract
Recently, the signs of extreme droughts, which were thought of as exceptional and unlikely, are being detected worldwide. It is necessary to prepare countermeasures against extreme droughts; however, current definitions of extreme drought are just used as only one or two indicators to [...] Read more.
Recently, the signs of extreme droughts, which were thought of as exceptional and unlikely, are being detected worldwide. It is necessary to prepare countermeasures against extreme droughts; however, current definitions of extreme drought are just used as only one or two indicators to represent the status or severity of a drought. More representative drought factors, which can show the status and severity that are relevant to extreme drought, need to be considered depending on the characteristics of the drought and comprehensive evaluation of various indices. Therefore, this study attempted to quantitatively define regional extreme droughts using more acceptable factors. The methodology comprises five factors that are indicative of extreme drought. The five factors are (1) duration (days), (2) number of consecutive years (years), (3) water availability, (4) return period, and (5) regional experience. The results were analyzed by applying the procedure to droughts that took place in 2014–2015 in South Korea. The results showed that the applied historical event did not enter the status of extreme drought, which is proposed in this study; however, the proposed methodology is applicable because it uses acceptable and reasonable factors to judge extreme drought, but it can also take into account the past regional experience of extreme drought. Full article
(This article belongs to the Special Issue Meteorological Extremes in Korea: Prediction, Assessment, and Impact)
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Open AccessFeature PaperArticle
Applicability Study of Pulsed Laser Beam Welding on Ferritic–Martensitic ODS Eurofer Steel
Metals 2020, 10(6), 736; https://doi.org/10.3390/met10060736 - 02 Jun 2020
Abstract
Pulsed laser beam welding was used successfully to join the oxide dispersion-strengthened (ODS) Eurofer steel. The joining was conducted with a laser power of 2500 W and a pulsed duration of 4 ms. With the filler material being used, a minor material loss [...] Read more.
Pulsed laser beam welding was used successfully to join the oxide dispersion-strengthened (ODS) Eurofer steel. The joining was conducted with a laser power of 2500 W and a pulsed duration of 4 ms. With the filler material being used, a minor material loss and microvoids were observed in the joint. The microstructure of the fusion zone consists of dual phase elongated structures. The heat-affected zone has a width of around 0.06 mm with finer grains. The transmission electron microscopy observation reveals that nanoprecipitates are finely distributed in the fusion zone. The tensile strength, yield strength and elongation of the joint are slightly inferior to the base material. The fractography results reveal a typical ductile fracture. The experimental results indicate a reasonable joint from the perspective of both the microstructure and mechanical behaviour. Full article
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Open AccessArticle
Effect of SiC/Fly Ash Reinforcement on Surface Properties of Aluminum 7075 Hybrid Composites
Coatings 2020, 10(6), 541; https://doi.org/10.3390/coatings10060541 - 02 Jun 2020
Abstract
Friction stir processing (FSP) has emerged as a valuable technique in the surface metal matrix composite fabrication field. In this process, solid-state processing mostly avoids the formation of detrimental phases inside composites. Despite having a high specific strength, further extensive Al alloy applications [...] Read more.
Friction stir processing (FSP) has emerged as a valuable technique in the surface metal matrix composite fabrication field. In this process, solid-state processing mostly avoids the formation of detrimental phases inside composites. Despite having a high specific strength, further extensive Al alloy applications are limited due to their poor surface properties. A hybrid reinforcement approach can be used to improve surface properties. In this study, industrial waste fly ash material is mixed with hard SiC ceramic particles. The main focus of this research is to improve wear resistance under dry sliding conditions and microhardness of aluminum 7075-T651 by dispersion of silicon carbide-fly ash (SiC/fly ash) powder in a base alloy by FSP. The parameters used for this investigation are: tool rotation rpm (500, 1000 and 1500), the tool traverse mm/min (20, 30 and 40), the reinforcement’s hybrid ratio HR (60:40, 75:25 and 90:10) and the volume percentage vol.% (4%, 8% and 12%). The influence of these parameters on the resultant composite’s microstructure, dry sliding wear rate and micro-hardness was studied. By using response surface methodology (RSM), desirable ranges of process parameters for lower wear rate and higher microhardness were obtained. The interaction effect of SiC/fly ash volume percentage and hybrid ratio had the most influential effect on the wear rates, as well as microhardness of composites. Moreover, microhardness increased with an increase in the volume percentage of SiC/fly ash powders towards high SiC content in hybrid ratio. Interestingly, among stirring parameters, tool traverse speed was found to be more influential than tool rotational speed. The minimum wear rate was observed for the Run 20 sample (w: 1000 rpm, v: 40 mm/min, HR: 75:25, vol.%: 8). A maximum microhardness of 241.20 HV was achieved for Run 15 (w: 500 rpm, v: 40 mm/min, HR: 90:10, vol.%: 12) sample. Mainly, reinforcement distribution—in accordance with the stirring action generated by the tool—had a major role in controlling the surface properties of the resultant composites. Full article
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Open AccessArticle
Metastable Austenite Transformation Kinetics of Medium-Carbon Silicon-Rich Steel during Partitioning in a Q & P Process
Metals 2020, 10(6), 738; https://doi.org/10.3390/met10060738 - 02 Jun 2020
Abstract
In the present study, quenching and partitioning (Q & P) treatment of a medium-carbon silicon-rich steel was processed by a dilatometer. The volume fraction of the retained austenite at different partitioning times was determined by X-ray diffraction (XRD). The metastable austenite transformation process [...] Read more.
In the present study, quenching and partitioning (Q & P) treatment of a medium-carbon silicon-rich steel was processed by a dilatometer. The volume fraction of the retained austenite at different partitioning times was determined by X-ray diffraction (XRD). The metastable austenite transformation process after different partitioning times was studied by a combination of dilatometry, XRD, and transmission electron microscopy (TEM). Analysis of the transformation kinetics of metastable austenite during partitioning by means of dilatometry and the Johnson–Mehl–Avrami–Kolmogorov (JMAK) equation was carried out. The results show that the volume fraction of retained austenite increases first and then decreases with the increase of the partitioning time. The transformation active energy Q = 141 kJ·mol−1 and the Avrami exponent n = 1. The transformation product of metastable austenite is needle-like bainite, which grows perpendicularly towards the boundary of the austenite. Finally, the blocky austenite was divided into lath-shaped forms. Full article
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Open AccessArticle
(−)-Loliolide Isolated from Sargassum horneri Protects against Fine Dust-Induced Oxidative Stress in Human Keratinocytes
Antioxidants 2020, 9(6), 474; https://doi.org/10.3390/antiox9060474 - 02 Jun 2020
Abstract
The emergence of fine dust (FD) among air pollutants has taken a toll during the past few decades, and it has provided both controversy and a platform for open conversation amongst world powers for finding sustainable solutions and effective treatments for health issues. [...] Read more.
The emergence of fine dust (FD) among air pollutants has taken a toll during the past few decades, and it has provided both controversy and a platform for open conversation amongst world powers for finding sustainable solutions and effective treatments for health issues. The present study emphasizes the protective effects of (–)-loliolide (HTT) isolated from Sargassum horneri against FD-induced oxidative stress in human HaCaT keratinocytes. The purification of (–)-loliolide was carried out by centrifugal partition chromatography. HTT did not show any cytotoxicity, and it further illustrated the potential to increase cell viability by reducing the reactive oxygen species (ROS) production in FD-stimulated keratinocytes. Furthermore, HTT suppressed FD-stimulated DNA damage and the formation of apoptotic bodies, and it reduced the population of cells in the sub-G1 apoptosis phase. FD-induced apoptosis was advancing through the mitochondria-mediated apoptosis pathway. The cytoprotective effects of the HTT against FD-stimulated oxidative damage is mediated through squaring the nuclear factor E2-related factor 2 (Nrf2)-mediated heme oxygenase-1 (HO-1) pathway, dose-dependently increasing HO-1 and NAD(P)H dehydrogenase (quinone) 1 (NQO1) levels in the cytosol while concomitantly improving the nuclear translocation of Nrf2. Future studies could implement the protective functionality of HTT in producing pharmaceuticals that utilize natural products and benefit the diseased. Full article
(This article belongs to the Special Issue Oxidative Stress Modulators and Functional Foods)
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Open AccessArticle
Microencapsulation of Pineapple Peel Extract by Spray Drying Using Maltodextrin, Inulin, and Arabic Gum as Wall Matrices
Foods 2020, 9(6), 718; https://doi.org/10.3390/foods9060718 - 02 Jun 2020
Abstract
A pineapple peel hydroalcoholic extract rich in phenolic compounds, was stabilized by microencapsulation using spray drying technology, with maltodextrin, inulin, and arabic gum as wall materials. The influence of the type of wall material and drying temperature (150 and 190 °C) on the [...] Read more.
A pineapple peel hydroalcoholic extract rich in phenolic compounds, was stabilized by microencapsulation using spray drying technology, with maltodextrin, inulin, and arabic gum as wall materials. The influence of the type of wall material and drying temperature (150 and 190 °C) on the particles properties was studied. The particles presented a spherical shape with a diameter ranging from approximately 1.3 to 18.2 µm, the exception being the ones with inulin that showed a large degree of agglomeration. All powders produced presented an intermediate cohesiveness and a fair to good flowability according to Carr index and Hausner ratio, which envisages suitable handling properties at an industrial scale. The microencapsulation processes using maltodextrin and arabic gum at 150 °C were the ones that showed higher maintenance of the antioxidant activity of compounds present in the extract before encapsulation during spray drying. In addition, the microparticles obtained were quite efficient in stabilizing the encapsulated phenolic compounds, as their antioxidant activity did not change significantly during six months of storage at 5 °C. Full article
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Open AccessReview
Mucoadhesive Electrospun Fibre-Based Technologies for Oral Medicine
Pharmaceutics 2020, 12(6), 504; https://doi.org/10.3390/pharmaceutics12060504 - 02 Jun 2020
Abstract
Oral disease greatly affects quality of life, as the mouth is required for a wide range of activities including speech, food and liquid consumption. Treatment of oral disease is greatly limited by the dose forms that are currently available, which suffer from short [...] Read more.
Oral disease greatly affects quality of life, as the mouth is required for a wide range of activities including speech, food and liquid consumption. Treatment of oral disease is greatly limited by the dose forms that are currently available, which suffer from short contact times, poor site specificity, and sensitivity to mechanical stimulation. Mucoadhesive devices prepared using electrospinning offer the potential to address these challenges by allowing unidirectional site-specific drug delivery through intimate contact with the mucosa and with high surface areas to facilitate drug release. This review will discuss the range of electrospun mucoadhesive devices that have recently been reported to address oral inflammatory diseases, pain relief, and infections, as well as new treatments that are likely to be enabled by this technology in the future. Full article
(This article belongs to the Special Issue Bioadhesive Systems for Topical Application)
Open AccessArticle
Punicalagin Protects Human Retinal Pigment Epithelium Cells from Ultraviolet Radiation-Induced Oxidative Damage by Activating Nrf2/HO-1 Signaling Pathway and Reducing Apoptosis
Antioxidants 2020, 9(6), 473; https://doi.org/10.3390/antiox9060473 - 02 Jun 2020
Abstract
The oxidative damage of the retinal pigment epithelium (RPE) is the early event that underlies the pathogenesis of maculopathies. Numerous studies have shown that punicalagin (PUN), a polyphenol present in pomegranate, can protect several cell types from oxidative stress. Our study aims to [...] Read more.
The oxidative damage of the retinal pigment epithelium (RPE) is the early event that underlies the pathogenesis of maculopathies. Numerous studies have shown that punicalagin (PUN), a polyphenol present in pomegranate, can protect several cell types from oxidative stress. Our study aims to establish if PUN protects RPE from UV radiation-induced oxidative damage. We used an experimental model which involves the use of a human-RPE cell line (ARPE-19) exposed to UV-A radiation for 1, 3, and 5 hours. ARPE-19 cells were pre-treated with PUN (24 h) followed by UV-A irradiation; controls were treated identically, except for UV-A. Effects of pre-treatment with PUN on cell viability, intracellular reactive oxygen species ROS levels, modulation of Nrf2 and its antioxidant target genes, and finally apoptosis were examined. We found that pre‑treatment with PUN: (1) antagonized the decrease in cell viability and reduced high levels of ROS associated with UV-A-induced oxidative stress; (2) activated Nrf2 signaling pathway by promoting Nrf2 nuclear translocation and upregulating its downstream antioxidant target genes (HO-1 and NQO1); (3) induced an anti-apoptotic effect by decreasing Bax/Bcl-2 ratio. These findings provide the first evidence that PUN can prevent UV-A-induced oxidative damage in RPE, offering itself as a possible antioxidant agent capable of contrasting degenerative eye diseases. Full article
(This article belongs to the Special Issue Pharmacological and Clinical Significance of Heme Oxygenase-1)
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Open AccessReview
An Update on Mitochondrial Reactive Oxygen Species Production
Antioxidants 2020, 9(6), 472; https://doi.org/10.3390/antiox9060472 - 02 Jun 2020
Abstract
Mitochondria are quantifiably the most important sources of superoxide (O2) and hydrogen peroxide (H2O2) in mammalian cells. The overproduction of these molecules has been studied mostly in the contexts of the pathogenesis of human diseases [...] Read more.
Mitochondria are quantifiably the most important sources of superoxide (O2) and hydrogen peroxide (H2O2) in mammalian cells. The overproduction of these molecules has been studied mostly in the contexts of the pathogenesis of human diseases and aging. However, controlled bursts in mitochondrial ROS production, most notably H2O2, also plays a vital role in the transmission of cellular information. Striking a balance between utilizing H2O2 in second messaging whilst avoiding its deleterious effects requires the use of sophisticated feedback control and H2O2 degrading mechanisms. Mitochondria are enriched with H2O2 degrading enzymes to desensitize redox signals. These organelles also use a series of negative feedback loops, such as proton leaks or protein S-glutathionylation, to inhibit H2O2 production. Understanding how mitochondria produce ROS is also important for comprehending how these organelles use H2O2 in eustress signaling. Indeed, twelve different enzymes associated with nutrient metabolism and oxidative phosphorylation (OXPHOS) can serve as important ROS sources. This includes several flavoproteins and respiratory complexes I-III. Progress in understanding how mitochondria generate H2O2 for signaling must also account for critical physiological factors that strongly influence ROS production, such as sex differences and genetic variances in genes encoding antioxidants and proteins involved in mitochondrial bioenergetics. In the present review, I provide an updated view on how mitochondria budget cellular H2O2 production. These discussions will focus on the potential addition of two acyl-CoA dehydrogenases to the list of ROS generators and the impact of important phenotypic and physiological factors such as tissue type, mouse strain, and sex on production by these individual sites. Full article
(This article belongs to the Special Issue Redox and Nitrosative Signaling and Stress)
Open AccessFeature PaperArticle
Rusty Blackbird Habitat Selection and Survivorship during Nesting and Post-Fledging
Diversity 2020, 12(6), 221; https://doi.org/10.3390/d12060221 - 02 Jun 2020
Abstract
Rusty blackbird (Euphagus carolinus) populations have declined dramatically since the 1970s and the cause of decline is still unclear. As is the case for many passerines, most research on rusty blackbirds occurs during the nesting period. Nest success is relatively high [...] Read more.
Rusty blackbird (Euphagus carolinus) populations have declined dramatically since the 1970s and the cause of decline is still unclear. As is the case for many passerines, most research on rusty blackbirds occurs during the nesting period. Nest success is relatively high in most of the rusty blackbird’s range, but survival during the post-fledging period, when fledgling songbirds are particularly vulnerable, has not been studied. We assessed fledgling and adult survivorship and nest success in northern New Hampshire from May to August in 2010 to 2012. We also assessed fledgling and adult post-fledging habitat selection and nest-site selection. The likelihood of rusty blackbirds nesting in a given area increased with an increasing proportion of softwood/mixed-wood sapling stands and decreasing distances to first to sixth order streams. Wetlands were not selected for nest sites, but both adults and fledglings selected wetlands for post-fledging habitat. Fledglings and adults selected similar habitat post-fledging, but fledglings were much more likely to be found in habitat with an increasing proportion of softwood/mixed-wood sapling stands and were more likely to be closer to streams than adults. No habitat variables selected during nesting or post-fledging influenced daily survival rates, which were relatively low for adults over the 60-day study periods (males 0.996, females 0.998). Fledgling survival rates (0.89) were much higher than reported for species of similar size. Full article
(This article belongs to the Special Issue Boreal Bird Ecology, Management and Conservation)
Open AccessArticle
Implications of Reduced Stand Density on Tree Growth and Drought Susceptibility: A Study of Three Species under Varying Climate
Forests 2020, 11(6), 627; https://doi.org/10.3390/f11060627 - 02 Jun 2020
Abstract
A higher frequency of increasingly severe droughts highlights the need for short-term measures to adapt existing forests to climate change. The maintenance of reduced stand densities has been proposed as a promising silvicultural tool for mitigating drought stress. However, the relationship between stand [...] Read more.
A higher frequency of increasingly severe droughts highlights the need for short-term measures to adapt existing forests to climate change. The maintenance of reduced stand densities has been proposed as a promising silvicultural tool for mitigating drought stress. However, the relationship between stand density and tree drought susceptibility remains poorly understood, especially across ecological gradients. Here, we analysed the effect of reduced stand density on tree growth and growth sensitivity, as well as on short-term drought responses (resistance, recovery, and resilience) of Scots pine (Pinus sylvestris L.), sessile oak (Quercus petraea (Matt.) Liebl.), and ponderosa pine (Pinus ponderosa Douglas ex C. Lawson). Tree ring series from 409 trees, growing in stands of varying stand density, were analysed at sites with different water availability. For all species, mean tree growth was significantly higher under low compared with maximum stand density. Mean tree growth sensitivity of Scots pine was significantly higher under low compared with moderate and maximum stand density, while growth sensitivity of ponderosa pine peaked under maximum stand density. Recovery and resilience of Scots pine, as well as recovery of sessile oak and ponderosa pine, decreased with increasing stand density. In contrast, resistance and resilience of ponderosa pine significantly increased with increasing stand density. Higher site water availability was associated with significantly reduced drought response indices of Scots pine and sessile oak in general, except for resistance of oak. In ponderosa pine, higher site water availability significantly lessened recovery. Higher site water availability significantly moderated the positive effect of reduced stand density on drought responses. Stand age had a significantly positive effect on the resistance of Scots pine and a negative effect on recovery of sessile oak. We discuss potential causes for the observed response patterns, derive implications for adaptive forest management, and make recommendations for further research in this field. Full article
(This article belongs to the Section Forest Ecology and Management)

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