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Changes of Frost Damage and Treeline Advance for Swiss Stone Pine in the Calimani Mts. (Eastern Carpathians, Romania)
KERN, Zoltán,POPA, Ionel
Acta Silvatica & Lignaria Hungarica , 2008,
Abstract: Checking the tree-ring structure of 39 living and 9 crossdated dead samples of Swissstone pine (Pinus cembra L.) collected from the upper timberline of the CalimaniMts. we haveidentified 59 frost rings over the past 250 years. We found concentrated occurrence of frost events inthree decades: in the 1790s, 1810s and 1910s. No frost ring was observed in two bidecadal periods:1750-1770 and 1850-1870. Out of the analysed interval 1963-2004 is the longest period without frostring occurrence. After 1920 both frequency and severity of frost events seem to decrease compared tothe prior 170 years. We determined the altitude of highest growing stone pine individuals in theBradului Ciont–Pietrosu region in June, 2006. Individuals were sorted into tree-form or bush-likemorphological groups. Mean elevation data of the groups were corrected by an estimated constant biasof GPS measurements (-30 m). Comparing the corrected values to early 20th century inventory data65 m and 95 m upward migration was determined for treeline and boundary of bush-like occurence,respectively. The parallel results suggest that the 20th century advance of the upper forest limit wasdue to the decrease of frost stress at the zone of timberline.
Optimal driving of isothermal processes close to equilibrium  [PDF]
Marcus V. S. Bonan?a,Sebastian Deffner
Physics , 2014, DOI: 10.1063/1.4885277
Abstract: We investigate how to minimize the work dissipated during nonequilibrium processes. To this end, we employ methods from linear response theory to describe slowly varying processes, i.e., processes operating within the linear regime around quasistatic driving. As a main result we find that the irreversible work can be written as a functional that depends only on the correlation time and the fluctuations of the generalized force conjugated to the driving parameter. To deepen the physical insight of our approach we discuss various self-consistent expressions for the response function, and derive the correlation time in closed form. Finally, our findings are illustrated with several analytically solvable examples.
Professional Driving and Adverse Reproductive Outcomes: The Evidence to Date and Research Challenges
Darren Mark Joubert
The Open Occupational Health & Safety Journal , 2009, DOI: 10.2174/1876216601001010001]
Abstract: The literature has reported widely on the adverse effects of whole-body vibration (wbv) exposure on professional drivers and the adverse health outcomes of lower back pain, and other musculoskeletal effects. Fewer reports exist on the adverse effects of wbv on the female reproductive system and foetal health and even less on the male reproductive system and function. This paper highlights some of the past and current literary evidence on the effects of wbv on the female and male reproductive systems and function as well as the possible reasons for the paucity of evidence in the literature. The difficulties in conducting epidemiological research in this field are explored with discussion on some of the major confounding factors which make it difficult to establish clear causal links between exposure and outcomes, especially for adverse reproductive effects.
Micrometeorological processes driving snow ablation in an Alpine catchment  [PDF]
R. Mott,L. Egli,T. Grünewald,N. Dawes
The Cryosphere , 2011, DOI: 10.5194/tc-5-1083-2011
Abstract: Mountain snow covers typically become patchy over the course of a melting season. The snow pattern during melt is mainly governed by the end of winter snow depth distribution and the local energy balance. The objective of this study is to investigate micro-meteorological processes driving snow ablation in an Alpine catchment. For this purpose we combine a meteorological boundary-layer model (Advanced Regional Prediction System) with a fully distributed energy balance model (Alpine3D). Turbulent fluxes above melting snow are further investigated by using data from eddy-correlation systems. We compare modeled snow ablation to measured ablation rates as obtained from a series of Terrestrial Laser Scanning campaigns covering a complete ablation season. The measured ablation rates indicate that the advection of sensible heat causes locally increased ablation rates at the upwind edges of the snow patches. The effect, however, appears to be active over rather short distances of about 4–6 m. Measurements suggest that mean wind velocities of about 5 m s 1 are required for advective heat transport to increase snow ablation over a long fetch distance of about 20 m. Neglecting this effect, the model is able to capture the mean ablation rates for early ablation periods but strongly overestimates snow ablation once the fraction of snow coverage is below a critical value of approximately 0.6. While radiation dominates snow ablation early in the season, the turbulent flux contribution becomes important late in the season. Simulation results indicate that the air temperatures appear to overestimate the local air temperature above snow patches once the snow coverage is low. Measured turbulent fluxes support these findings by suggesting a stable internal boundary layer close to the snow surface causing a strong decrease of the sensible heat flux towards the snow cover. Thus, the existence of a stable internal boundary layer above a patchy snow cover exerts a dominant control on the timing and magnitude of snow ablation for patchy snow covers.
Micrometeorological processes driving snow ablation in an Alpine catchment  [PDF]
R. Mott,E. Egli,T. Grünewald,N. Dawes
The Cryosphere Discussions , 2011, DOI: 10.5194/tcd-5-2159-2011
Abstract: Mountain snow covers typically become patchy over the course of a melting season. The snow pattern during melt is mainly governed by the end of winter snow depth distribution and the local energy balance. The objective of this study is to investigate micrometeorological processes driving snow ablation in an Alpine catchment. For this purpose we combine a meteorological model (ARPS) with a fully distributed energy balance model (Alpine3D). Turbulent fluxes above melting snow are further investigated by using data from eddy-correlation systems. We compare modelled snow ablation to measured ablation rates as obtained from a series of Terrestrial Laser Scanning campaigns covering a complete ablation season. The measured ablation rates indicate that the advection of sensible heat causes locally increased ablation rates at the upwind edges of the snow patches. The effect, however, appears to be active over rather short distances except for very strong wind conditions. Neglecting this effect, the model is able to capture the mean ablation rates for early ablation periods but strongly overestimates snow ablation once the fraction of snow coverage is below a critical value. While radiation dominates snow ablation early in the season, the turbulent flux contribution becomes important late in the season. Simulation results indicate that the air temperatures appear to overestimate the local air temperature above snow patches once the snow coverage is below a critical value. Measured turbulent fluxes support these findings by suggesting a stable internal boundary layer close to the snow surface causing a strong decrease of the sensible heat flux towards the snow cover. Thus, the existence of a stable internal boundary layer above a patchy snow cover exerts a dominant control on the timing and magnitude of snow ablation for patchy snow covers.
Contrasting short-term performance of mountain birch (Betula pubescens ssp. czerepanovii) treeline along a latitudinal continentality-maritimity gradient in the southern Swedish Scandes  [cached]
Lisa ?berg,Leif Kullman
Fennia : International Journal of Geography , 2012,
Abstract: Positional treeline shift is a fundamental aspect and indicator of high-mountain vegetation response to climate change. This study analyses treeline performance during the period 2005/2007 -2010/2011 in the Swedish Scandes. Focus is on mountain birch (Betula pubescens ssp. czerepanovii) along a regional climatic maritimity-continentality gradient. Treeline upshift by 3.0 yr-1 in the maritime part differed significantly from retreat by 0.4 m yr-1 in the continental part of the transect. This discrepancy is discussed in terms of differential warming-induced snow cover phenology patterns and their influence on soil moisture conditions. In the continental area, earlier and more complete melting of prior relatively rare late-lying snow patches, even high above the treeline, has progressed to a state when melt water irrigation ceases. As a consequence, soil drought sets back the vigor of existing birches and precludes sexual regeneration and upslope advance of the treeline. In the maritime area, extensive and deep snow packs still exist above the treeline and constrain its position, although some release is taking place in the current warm climate. Thereby, the birch treeline expands upslope as the alpine snow patches shrink, but continue to provide sufficient melt water throughout the summer. Treeline rise appears to have been based primarily on seed regeneration over the past few decades. This is a novelty, since prior (1915-2007) treeline advance was accomplished mainly by in situ shifts in growth form of relict krummholz birches, in some cases millennial-old, prevailing above the treeline. By the snow phenology mechanism, birch can benefit from climate warming in the maritime region, which contrasts with the situation in the continental region. This discrepancy should be accounted for in projective models. In a hypothetical case of sustained warming, the subalpine birch forest belt may expand less extensively than often assumed, although advance may continue for some time in snow rich maritime areas.
Nonlinear Landau-Zener Processes in a Periodic Driving Field  [PDF]
Qi Zhang,Peter Hanggi,Jiangbin Gong
Physics , 2008, DOI: 10.1088/1367-2630/10/7/073008
Abstract: Effects of a periodic driving field on Landau-Zener processes are studied using a nonlinear two-mode model that describes the mean-field dynamics of a many-body system. A variety of different dynamical phenomena in different parameter regimes of the driving field are discussed and analyzed. These include shifted, weakened, or enhanced phase dependence of nonlinear Landau-Zener processes, nonlinearity-enhanced population transfer in the adiabatic limit, and Hamiltonian chaos on the mean field level. The emphasis of this work is placed on how the impact of a periodic driving field on Landau-Zener processes with self-interaction differs from those without self-interaction. Aside from gaining understandings of driven nonlinear Landau-Zener processes, our findings can be used to gauge the strength of nonlinearity and for efficient manipulation of the mean-field dynamics of many-body systems.
Developing Framework to Test Driving Performance at Left-Turn Movement with In-Vehicle Advance Collision Warning Message  [PDF]
Mahreen Nabi, Fengxiang Qiao, Boya You, Lei Yu
Journal of Transportation Technologies (JTTs) , 2016, DOI: 10.4236/jtts.2016.61004
Abstract: Left-turning traffic without a protected left-turn signal is one of the major safety concerns at urban intersections. Though an average of only l0% - 15% of all approaching traffic turns left, significantly a large proportion of left-turn crashes occur involving 21% of all intersection fatal crashes. Where traditional safety countermeasures of signal timing-phasing and use of flashing yellow light have reportedly failed to significantly reduce the rate of crashes, an in-vehicle advance collision warning message can be helpful to reduce left-turn collisions at intersections. In this study, an in-vehicle audio warning application has been designed by providing two safety warning messages (Advance Warning Message and Safe Left-turn Maneuver Message) under the vehicle to vehicle (V2V) communication system, which is triggered based on the acceptable gaps of oncoming opposing vehicles for a safe left-turn. A driving simulator test has been conducted with 30 participants to investigate the impacts of warning messages on performance measures such as speed and acceleration profiles, collision records, brake reaction distance, and intersection clearance time. Statistical results showed that with the help of these messages, all participants were able to reduce speeds and accelerations and chose suitable gaps without potential conflicts. Moreover, the results of questionnaire analysis provide a positive acceptability especially for the Safe Left-turn Maneuver Message. Based on the performance measurements, this type of safety warning messages can be recommended for possible real-road tests for practical applications.
Subalpine Forest and Treeline Ecotone under the Influence of Disturbances: A Review  [PDF]
Friedrich-Karl Holtmeier, Gabriele Broll
Journal of Environmental Protection (JEP) , 2018, DOI: 10.4236/jep.2018.97051
Abstract: This article considers disturbances caused by abiotic and biotic factors and human impact in the ecological region extending from subalpine forest to the upper tree limit. Both abiotic and biotic factors may cause reversible or irreversible disturbances. Disturbances by mass movement and avalanches give the subalpine forest and the treeline ecotone a distinct spatial pattern characterized by forest on safe topography and sites that preclude forest. Removal of the upper subalpine forests by humans has enlarged the snow-catchment area of avalanches and elongated the avalanche pathways. Consequently, avalanche destructive potential has increased. Hazards will probably increase due to climate change. External factors, like cyclonic storms, may cause fundamental disturbances. Fires have played a major role in the removal of high-elevation forests. Forest destruction by fire is often followed by soil erosion. Wild fires are likely to increase as a result of warming climate and would possibly prevent climatically-driven treeline advance. Cyclic or episodic mass outbreaks of defoliating insects and bark beetles, and pathogens also cause severe disturbances. Oversized populations of wild ungulates impede tree regeneration and can cause local soil erosion. Inadequate game management is the primary cause of intolerable ungulate numbers. Due to man-caused habitat fragmentation, the animals’ impact on the remained habitats has increased. Subalpine forest may recover from disturbance or become replaced by a substitute formation (e.g. krummholz). A subsequent absence of natural disturbances may also be considered a disturbance initiating a new development. Both natural and anthropogenic disturbances may counteract positive influences of climatic warming on subalpine forests and treeline. Effective measures to reduce or prevent abiotic and biotic disturbances of high-elevation forest may contribute to greater safety for people living in the endangered areas of the mountain valleys and also improve other ecosystem services of the subalpine forest.
Functional Traits Reveal Processes Driving Natural Afforestation at Large Spatial Scales  [PDF]
Norman W. H. Mason, Susan K. Wiser, Sarah J. Richardson, Michael J. Thorsen, Robert J. Holdaway, Stéphane Dray, Fiona J. Thomson, Fiona E. Carswell
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0075219
Abstract: An understanding of the processes governing natural afforestation over large spatial scales is vital for enhancing forest carbon sequestration. Models of tree species occurrence probability in non-forest vegetation could potentially identify the primary variables determining natural afforestation. However, inferring processes governing afforestation using tree species occurrence is potentially problematic, since it is impossible to know whether observed occurrences are due to recruitment or persistence of existing trees following disturbance. Plant functional traits have the potential to reveal the processes by which key environmental and land cover variables influence afforestation. We used 10,061 survey plots to identify the primary environmental and land cover variables influencing tree occurrence probability in non-forest vegetation in New Zealand. We also examined how these variables influenced diversity of functional traits linked to plant ecological strategy and dispersal ability. Mean annual temperature was the most important environmental predictor of tree occurrence. Local woody cover and distance to forest were the most important land cover variables. Relationships between these variables and ecological strategy traits revealed a trade-off between ability to compete for light and colonize sites that were marginal for tree occurrence. Biotically dispersed species occurred less frequently with declining temperature and local woody cover, suggesting that abiotic stress limited their establishment and that biotic dispersal did not increase ability to colonize non-woody vegetation. Functional diversity for ecological strategy traits declined with declining temperature and woody cover and increasing distance to forest. Functional diversity for dispersal traits showed the opposite trend. This suggests that low temperatures and woody cover and high distance to forest may limit tree species establishment through filtering on ecological strategy traits, but not on dispersal traits. This study shows that ‘snapshot’ survey plot data, combined with functional trait data, may reveal the processes driving tree species establishment in non-forest vegetation over large spatial scales.
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