Winter Extent Research Articles

Recent changes in mountain birch forest structure and understory vegetation depend on the seasonal timing of reindeer grazing

Abstract Subarctic forest‐tundra ecotones dominated by mountain birch (Betula pubescens ssp. czerepanovii) are an important habitat for semi‐domestic reindeer Rangifer tarandus. The seasonal timing of reindeer grazing may direct vegetation trajectories in these systems, because in the summer ranges, mountain birches are subjected to browsing, while in the winter ranges, reindeer feed on understorey vegetation and arboreal lichens but leave the mountain birches intact. Based on earlier research, we predicted that (a) summer browsing dampens ongoing vegetation ‘shrubification’ in semi‐dry and dry mountain birch forests and (b) ‘shrubification’ is accompanied by a decline in lichens. We tested these predictions through re‐analysing forest structure and understorey vegetation after 12 years in areas where winter and summer ranges had been separated since the 1980s. We also tested how changes in lichen abundances align with changes in shrub abundances through correlation analyses. The number of tall mountain birch seedlings had increased twice as fast in winter than summer ranges, while big mountain birches had increased in summer ranges. The dominant evergreen dwarf shrub mountain crowberry (Empetrum nigrum ssp. hermaphroditum) had increased to a greater extent in winter ranges in a semidry habitat, and to a greater extent in summer ranges in a dry habitat. Deciduous dwarf shrub and graminoid biomass had increased similarly in summer and winter ranges. We found no evidence to support that increasing shrub abundances had contributed to a decline in lichens; instead, the lichen cover increased with increasing number of mountain birch seedlings. Synthesis and application. The vegetation trajectories of dry and semi‐dry subarctic mountain birch forests depend greatly on whether the area is used as a winter or a summer range for the reindeer. The recent changes in vegetation are likely to lead to improved summer forage availability for the reindeer, while the opposite may be true for the winter forage availability.

Extreme oceanographic conditions in the northwestern Bering Sea in 2017–2018

Anomalous oceanographic conditions were observed in the northwestern Bering Sea in 2017–2018, including warmer air and water temperatures and reduced ice cover. Their effects on the water structure and circulation are considered. These conditions were formed on the background of warming tendency known in the Bering Sea since 2014, but the year 2018 was exceptional even relative to this background. In this year, deflections of some properties from their mean values exceeded two standard deviations (>2σ). The main reason for such abnormal conditions was southerly winds prevailed over the entire sea in winter because of a westward shift of the Aleutian Low; another factor was the strengthened advection of oceanic waters that still were abnormally warm after the period of extreme warming in the North-East Pacific in 2014–2016. As the result, the ice extent in winter and spring was below its mean value (more than twice lower in 2018), the air and water temperatures were above their mean values through the year (up to 15 and 3 °C higher, respectively, in 2018), the cold water mass was not formed at the shelf bottom in winter and was absent in summer. Under this considerable redistribution of water density, the water circulation changed, the Navarin Current weakened and was even absent in fall 2018/ and the northward water transport toward the Bering Strait was realized through the eastern shelf and delivered the coastal waters from Alaska instead of the waters from the deep-water basins, as has been usual. The oceanographic conditions in 2018 were statistical outliers, atypical even for recent period of warming, but such conditions could be expected if the warming continues. Thus, the phenomenon of 2017–2018 could be useful for understanding and predicting the reconstruction of the oceanographic regime in the near future.

Disentangling the Coupled Atmosphere‐Ocean‐Ice Interactions Driving Arctic Sea Ice Response to CO2 Increases

AbstractA novel decomposition of the ocean heat energy that contributes to sea ice melt and growth (ocean‐ice and frazil heat) into components that are driven by surface heat flux and ocean circulation changes is used to isolate the evolving roles of the atmosphere and ocean in the Arctic sea ice loss from CO2 increases. A sea ice volume budget analysis is used to separate the impacts of the anomalous frazil/ocean‐ice heat from those of atmosphere‐ice heat on the evolving Arctic sea ice volume. The role of atmosphere‐ocean coupling in augmenting or curtailing the atmosphere‐ and ocean‐driven sea ice losses is further isolated by comparing the ice volume budget and the anomalous frazil/ocean‐ice heat components in partially and fully coupled experiments. Atmosphere‐ice heat fluxes drive most of Arctic sea ice loss in the first decade following CO2 increase by increasing the sea ice top face melt in summer, while ocean circulation changes drive the loss over the longer term through the anomalous increase of heat transport into the Arctic, which drive decreases in frazil ice growth and sea ice extent in winter. Atmosphere‐ocean coupling in the subpolar Atlantic further supports a negative feedback that attenuates the ocean‐driven sea ice losses over time; by accelerating the weakening of the Atlantic meridional overturning circulation, it causes a large cooling of the subpolar Atlantic and attenuation of the anomalous heat transport into the Arctic in winter, allowing for a seasonal Arctic sea ice in the fully coupled experiment, while the Arctic completely becomes ice free in the partially coupled experiment.

Climate change patterns in precipitation over Spain using CORDEX projections for 2021–2050

This work presents an analysis of the climate change scenarios in some extreme precipitation indices over Spain using simulations from the EURO-CORDEX project. Change projections of precipitation are evaluated for the near future (2021–2050) relatively to a reference past climate (1971–2000). Projections of annual precipitation show a general decrease in almost the whole region except over the central area where positive changes are detected due to a significant increase in winter. For consecutive wet days, an annual decrease is also projected over the country attributable to a significant decrease mainly observed in spring and to a lesser extent in winter. On the other hand, consecutive dry days are projected to be higher overall as a result of significant increases in spring, summer and autumn. Positive changes are also projected for the maximum daily precipitation during winter and autumn.

Possible influence of the tropospheric polar vortex on the Barents Sea ice extent in winter

The Arctic seas are mainly located inside the polar vortex under conditions of low temperature. Sea ice extent in these seas in the winter-spring period reaches maximum values with negligible interannual changes. The exception is the Barents Sea, where interannual variability of sea ice extent increases from December to February. In winter, the vortex edge is often located near the Barents Sea, which leads to an increase in surface temperature and a decrease in sea ice extent. We show that the Barents Sea ice extent in winter can be determined by the shape and location of the tropospheric polar vortex.

Assessment of trace metal accumulation in native mussels (Brachidontes rodriguezii) from a South American temperate estuary.

The present work provides the first results in heavy metal bioaccumulation in the autochthonous mussel Brachidontes rodriguezii from the Bahía Blanca Estuary (Argentina), one of the most important coastal environments of South America, subjected to different anthropogenic pressure. The study is based on the detection of Cd, Cu, Pb, Mn, and Fe in mussels' soft tissue and sediments' fine fraction by means of inductively coupled plasma atomic emission spectroscopy (ICP-OES), in order to analyze the potential relationship between both components of the aquatic system. Additionally, different indices are calculated with the purpose of obtaining detailed data. The heavy metal burden in mussels varied seasonally, showing a clearer pattern for the stations located in the internal area of the estuary. Metals exhibited maximum values in summer and to a lesser extent in winter, followed by a decrease during spring. Multiple international guideline assessment allowed classifying the area as moderately polluted, including a low range for Cd and medium for Cu and Pb. Moreover, the average detected levels were within the measured ranges in other coastal areas. Regarding human health, trace metal content in mussels met the national and international standards for safe consumption.

Heating Assist System for Liquid Tank Using Shallow Geothermal Energy via Heat Pipe BACH

This study aims to develop a heating assist system for liquid tanks by using shallow geothermal energy via a new type of heat pipe named Bubble-Actuated Circulating Heat pipe (BACH). In this system, BACH transports heat from shallow underground (temperature remains constant at around 15 °C in Fukui) to the liquid of caustic soda solution (49 wt%, freezing point is about 5 °C) preserved in the tank. From a previous simplified small-scale experiment, we concluded that BACH could warm the liquid to some extent in winter. In this report, experimental results of field tests are demonstrated where 10 m3 tank equipped with an electric heater as an auxiliary heater was tested and five sets of BACH were installed. As a result, this system could warm the liquid at about 7 °C only by BACH without electricity under the experimental conditions tested.

The influence of surface versus free-air decoupling on temperature trend patterns in the western United States

[1] We analyzed temperature trends from 460 GHCNv2 weather stations in the western United States for 1948–2006 to determine whether the extent of decoupling of surface temperatures from the free atmosphere influences past change. At each location we derived monthly indices representative of anticyclonicity using NCEP/NCAR 700 hPa reanalysis pressure fields. The number of anticyclonic days minus cyclonic days (A–C) is positively correlated with temperature anomalies at exposed convex sites and in the north of the domain where the free atmosphere controls temperature, anticyclonic months being warmer. In topographic concavities, and in the south of the domain where the influence of upper air ridges and troughs is muted, the relationship is much weaker. We use the gradient of the A–C index–temperature relationship to represent a coupling index, highest at exposed free-air locations. On a mean annual basis there are no strong relationships between temperature trend magnitude, elevation, topographic incision, or coupling index. However, in winter, warming is weaker at decoupled locations, especially when snow cover is present. Where snow is absent in winter, and in fall, the relationship is reversed. Circulation changes (increased cyclonicity) can explain the disparity in warming between decoupled and exposed locations in fall and to a certain extent in winter (increased anticyclonicity), although winter results are also regionally sensitive. Thus, future climate change may be different (amplified or muted dependent on season and/or surface characteristics) in locations prone to surface decoupling, compared with locations exposed to the free atmosphere. Understanding such processes will aid downscaling of future climate change.

Atmospheric‐driven state transfer of shore‐fast ice in the northeastern Kara Sea

Frequencies of observed occurrences of shore‐fast ice in the northeastern Kara Sea for each month during 1953–1990 reveal a multimodality of shore‐fast ice extent in late winter and spring. The fast ice extent exhibits mainly three different configurations (modes) associated with the regional topography of coasts and islands. These modes show fast ice areas equal to approximately 98 ± 6, 122 ± 6, and 136 ± 8 1000 km2. Analysis of the time series of fast ice extent shows that favorable conditions for expansion of fast ice seaward in winter and spring are met if the atmospheric circulation over the northeastern Kara Sea is controlled by the Arctic high, resulting in offshore winds and a significant (up to 6°C) decrease of the monthly mean surface air temperature. In contrast, the penetration of the Icelandic low into the Kara Sea, accompanied by Arctic cyclones coming from the west, is responsible for the partial breakup and decrease of fast ice extent in winter or spring.

Nutrient Digestion of Common Bermudagrass (Cynodon dactylon L.) Pers Growing in Northeastern Mexico

Ramírez, R.G., González-Rodríguez, H. and García-Dessommes, G. 2002. Nutrient digestion of common bermudagrass (Cynodon dactylon L.) Pers growing in northeastern Mexico. J. Appl. Anim. Res., 23: 93–102. The rate and extent of nutrient digestion of total plant, leaves and steins of common bermudagrass were estimated using the nylon bag technique in rumen fistulated Pelibuey × Rambouillet sheep fed alfalfa hay. The crude protein (CP) content of common bermudagrass during spring was higher and lower during winter. Leaves resulted with higher (P<0.05) CP than stems. The neutral detergent fiber (NDF) and its derivatives (hemicellulose, cellulose, lignin and insoluble ash) were lower (P<0.05) in spring and higher in winter. There was no difference (P>0.05) in NDF between leaves and stems; however, lignin was lower (P>0.05) in leaves than that in stems. Dry matter, crude protein and cell wall of common bermudagrass were better digested during spring by rumen microbes in sheep and to a lower extent in winter. Leaves resulted in higher nutrient degradabilities than steins. In general, during spring mineral contents were higher and lower in winter. During spring when precipitation was high (417 mm out of 613 mm), nutrient content of common bermudagrass was higher than that in other seasons.

On the mating system of polar bears

Polar bears are intimately associated with arctic sea ice and their distribution is approximated by its winter extent. They are the only terrestrial mammals, other than humans, to have adapted so completely to sea ice, a quite different habitat, spatially and temporally, from that occupied by other terrestrial mammals. We propose that the dynamics of sea ice and the associated variability in access to food have played a major role in the evolution of the social structure and mating system of polar bears. Adult females and males move to areas of the sea ice where the greatest success in hunting is realized. Such regions are unpredictable in location, however, both seasonally and annually. Because female distributions are unpredictable, adult males are unable to defend stable territories that will encompass the home ranges of one or more females and may instead distribute themselves among different sea-ice habitats at the same relative densities as solitary adult females. Females keep nursing cubs with them for more than 1 year; hence the mean interbirth interval is 2 or more years. This results in a functionally skewed sex ratio, with fewer females available to breed in any one year than males, and in intrasexual competition among males for access to breeding females. Consequently, established dominance hierarchies among males are unstable, and wounding, scarring, and breakage of canine teeth are common; these are evidence of direct physical confrontations during the breeding season. Large body size is advantageous in these fights and this has resulted in one of the highest degrees of sexual dimorphism among terrestrial mammals. Because of the funtionally skewed sex ratio and the shifting distribution of both females and males, however, even the largest male probably cannot be certain of locating a larger than average number of receptive females in any one breeding season.

The role of plant hormones in higher plant cellular differentiation. II. Experiments with the vascular cambium, and sclereid and tracheid differentiation in the pine, Pinus contorta.

In sterile-cultured explants of stems of the pine Pinus contorta Dougl., fusiform cambial cells differentiated entirely into axial parenchyma cells when exogenous indol-3yl-acetic acid (IAA) was omitted. The normal appearance of the cambial zone was maintained when IAA was included in the medium. The IAA-maintained stability of cambial structure suggests physiological rather than epigenetic control over vascular cambium structure. IAA was essential for the occurrence of callus growth in stem explants. Callus growth was similar in appearance and extent in winter- and summer-explanted material. Tracheids differentiated in explants only when actively differentiating tracheids were already present at the moment of explanting, suggesting the absence of factors necessary for tracheid differentiation in over-wintering tissues. Sclereid differentiation, which normally does not occur in phloem or xylem development in P. contorta, occurred in callus derived from active cambial explants. The sclereids were identical to sclereids which differentiated in pith of intact stems. The possibility that sclereid and tracheid differentiation may be fundamentally similar types of gene expression is discussed. Growth of P. contorta trees in continuous darkness resulted in extensive compression-wood tracheid differentiation in the upright main stem. Normal-wood tracheids differentiated in similar trees grown in light. More tracheids differentiated in light than in darkness. This apparently is the first report of induction of compression-wood tracheid differentiation in the absence of hormone treatment or tilting of trees. Different types and numbers of tracheids differentiated at different position in two-year-old disbudded defoliated stem cuttings of P. contorta in response to apically supplied IAA. No evidence for new tracheid differentiation was seen in control cuttings; however, the results suggest that neither cambial cell division nor tracheid differentiation were actually initiated by IAA. Directed transport of additional regulatory factors toward areas of high IAA concentration is formulated as a hypothesis to explain these observations. Gibberellic acid, (S)-abscisic acid and IAA inhibited tracheid differentiation when individually supplied to basal ends of P. contorta cuttings predisposed to differentiate new tracheids. Experiments with single intact needles on Pinus cembroides var. monophylla cuttings confirmed a previous interpretation that the mature pine needle, rather than the short-shoot apical meristem at its base, promotes tracheid differentiation in the stem.

Ixodes ricinusin Relation to its Physical Environment

The biotic factors in the environment of the tick,Ixodes ricinus, exercise little effect on the geographical or local distribution of the species, or on its seasonal prevalence.The local distribution is determined by edaphic factors, a wet, mossy, or peat soil and a dense mat of old vegetation or a rank growth being necessary for survival of the tick. In Britain, the critical season for survival is summer, during which the moisture factor in the microclimate acts in a limiting capacity.The seasonal prevalence is determined by temperature. Within limits, which appear to correspond to air-temperature limits of 7 and 16° C. (weekly maxima), the unfed tick climbs the vegetation, and thus readily obtains a host. In Britain, it is inactivated in winter by the cold, and in summer it is less readily picked up by hosts because of its positive geotropic response to the stimulus of high temperatures.The summer is, in Britain, the optimum season for development, which also proceeds to some extent in winter. Autumn and spring are parasitisation seasons. The life cycle, involving a parasitisation and a development season for each stage, requires a minimum of 1½ years. The period may extend to 4½ years.The possible world distribution of the species is limited primarily by temperature. Thus, microclimatic extremes of — 14 and 35° C. limit the range through which the tick can survive. A period of at least 3 months with the mean air temperatures over 10° C. is necessary for development, while the mean air temperature of the coldest month must not exceed 10° C. to allow of parasitisation occurring.Within the areas delimited in relation to the temperature requirements of the tick, distribution is governed by the moisture factor. An index of the suitability of an area within the temperature limits is afforded by the type of vegetation; forest and woodland, including grass and cultivation areas, as opposed to prairie and steppe, indicate suitable moisture conditions.