Paleovegetation and Paleoclimatic Changes in the Yukon at 6 ka BP

The most recent paleoenvironmental change to affect the Yukon centres around 6.0 ka. In the forested southern Yukon, black spruce (Picea mariana) and green alder (Alnus crispa) expanded their populations at most sites between 6.5 and 6.0 ka. Even in the semi-arid region of SW Yukon these species increased their populations, although slightly later at 5.5 ka. These vegetation changes in the south imply cooler and wetter growing seasons, i.e. more mesic conditions. In the region of the upper Blackstone River of central Yukon, the modern vegetation consists of shrub tundra with scattered groves of white spruce (Picea glauca) and even fewer black spruce. Open forests of predominantly white spruce occupied the region as early as 9.5 ka, but between 6.5 and 6.0 ka white spruce declined as black spruce became the dominant tree, coincidentally with an increase in green alder. By 5.0 ka the vegetation had acquired its modern composition. As in the south, these changes imply cooling. Less evidence is available on the expansion of alder and black spruce in the northern Yukon. Both species increased in forested areas (forest-tundra) at 6.0 ka. These changes again imply cooling. Because both black spruce and green alder were present in Yukon well before 6 ka, these vegetation changes cannot be ascribed to migration lags.Les changements apportés à la paléovégétation et au paléoclimat du Yukon à 6 ka BP. Au Yukon, les changements environnementaux les plus récents se sont produits vers 6 ka. Dans les zones forestières du sud du Yukon, l'épinette noire (Picea mariana) et l'aulne crispé (Alnus crispa) ont vu leur population augmenter entre 6,5 et 6 ka dans la plupart des sites. Même dans la région semi-aride du sud-ouest du Yukon, ces espèces ont connu une augmentation, bien qu'elle se soit produite plus tard, soit vers 5,5 ka. Ces changements dans la végétation méridionale du Yukon signalent l'avènement de saisons végétatives plus fraîches et plus humides, c'est-à-dire des conditions plus mésiques. Dans la région du cours supérieur de la Blackstone River, au centre du Yukon, Ia végétation moderne se compose d'une toundra arbustive parsemée ça et là de colonies d'épinettes blanches (Picea glauca) et de rares épinettes noires. Les forêts ouvertes dominées par l'épinette blanche peuplaient la région jusqu'à 9,5 ka, mais entre 6,5 et 6 ka, l'épinette blanche a décliné au profit de l'épinette noire, en concomitance avec une augmentation de l'aulne crispé. Vers 5 ka, la végétation avait acquis son caractère moderne. Tout comme au sud, ces changements impliquent un refroidissement. Il existe moins d'indices quant à l'expansion de l'aulne et de l'épinette noire dans le nord du Yukon. Les deux espèces se sont répandues dans les zones forestières (toundra forestières) à 6 ka. Encore une fois, il dut y avoir refroidissement. Puisque l'épinette noire et l'aulne crispé étaient présents dans le Yukon bien avant 6 ka, on ne peut attribuer ces changements enregistrées par la végétation à des décalages migratoires.Palàovegetation und palâoklimatische Verânderungen im Yukon um 6 ka v.u.Z. Die jùngsten Palâoumweltverànderungen im Yukon sind um etwa 6.0 ka geschehen. Im bewaldeten sùdlichen Yukon haben Schwarzfichte (Picea mariana) und grùne Erie (Alnus crispa) ihre Population an den meisten Plàtzen zwischen 6.5 und 6.0 ka erhôht. Selbst in der halbtrockenen Region von Sùdwest-Yukon haben dièse Arten ihre Populationen erhôht, wenn auch etwas spâter, um 5.5 ka. Dièse Vegetations-Wechsel im Sùden weisen auf kùhlere und feuchtere Wachstumszeiten, d.h. mehr mittlere Bedingungen. Im Gebiet des oberen Laufs des Blackstone River von Zentral-Yukon besteht die moderne Vegetation aus Busch-Tundra mit verstreuten Wâldchen von WeiBfichte (Picea glauca) und noch weniger Schwarzfichte. Offene Wàlder vor allem mit WeiBfichte bevôlkerten die Region so fruh wie 9.5 ka, aber zwischen 6.5 und 6.0 ka nahm die WeiBfichte ab, wàhrend die Schwarzfichte der beherrschende Baum wurde, begleitet von einer Zunahme von grùner Erie. Um 5.0 ka hatte die Vegetation ihre moderne Zusammensetzung erreicht. Wie im Sùden beinhalten dièse Verânderungen eine Abkùhlung. Ùber die Ausdehnung von Erie und Schwarzfichte im nôrdlichen Yukon gibt es weniger Belege. Beide Arten nahmen in bewaldeten Gebieten (Wald-Tundra) um 6.0 ka zu. Auch hier bedeuten die Wechsel eine Abkùhlung. Da beide, Schwarzfichte und grùne Erie, lange vor 6 ka im Yukon vorhanden waren, kann man dièse Vegetationswechsel nicht Verzôgerungen bei der Wanderung zuschreiben

Reversion of forest to tundra in the central Yukon

Pollen and plant macrofossil analyses of sediments from 3 sites that are presently in shrub tundra provide a record of former forest establishment. Shrub tundra with groves and gallery forests of balsam poplar Populus balsamea occupied the region between 10 000-8000 BP. At 9400 BP white spruce Picea glauca populations expanded, and open white spruce woodlands persisted until 6500 BP when black spruce Picea mariana and green alder Alnus viridis populations increased, resulting in open spruce woodlands with a distribution of species probably similar to that commonly found today in the northern boreal forest: white spruce on drier S-facing slopes and on alluvial sites with balsam poplar, and black spruce on colder, wetter sites on N-facing slopes and valley bottoms. At 5000 BP forest began to revert to shrub tundra, abruptly then more gradually. The modern groves of (mostly white) spruce are probably relict populations surving in favorable microsites. The ground vegetation apparently behaved independently of the tree populations. -from Author

L’environnement tardiglaciaire du Yukon septentrional, Canada

Le site des grottes du Poisson-Bleu, localisé sur une assise à calcaires dévoniens au sein de la forêt boréale du Yukon septentrional, a fourni, en plus d'un abondant matériel paléontologique et de quelques données archéologiques, des sédiments pollinifères. Le diagramme pollinique d'un dépôt consistant en un loess tardiglaciaire recouvert d'un humus à cailloutis d'âge holocène présente un assemblage inférieur dominé par des herbes de toundra et un assemblage supérieur dominé par l'épinette et l'aulne. Grâce à ces données ainsi qu'à celles tirées de sites avoisinants, il est possible d'en arriver à une reconstitution de la végétation dont les phases importantes sont les suivantes: une période tardiglaciaire, de 16 000 à 12 000 BP, caractérisée par une toundra herbacée, éparse sur les hauts plateaux et par des marécages à laiches et à graminées dans les basses terres; ultérieurement, au cours de l'Holocène, le phénomène d'entourbement du sol et le développement de bruyères et de pessières, conséquences d'un climat plus chaud.The Bluefish Caves site, located on a scarp of Devonian limestone in the northern boreal forest of the Yukon, has yielded pollen-bearing sediments in addition to abundant paleontological and some archaeological data. A pollen diagram based on samples of late-glacial lcess overlain by Holocene humus shows two main pollen assemblages, the lower dominated by herbs and dwarf shrubs and the upper by spruce and alder. Based on these results, but also drawing on recent findings from other sites in N. Yukon, we offer the following reconstruction of the vegetation history of the region. The vegetation of the late-glacial period, from 16 000 to 12 000 BP, was a sparse herb tundra on upland surfaces and a complex of sedge-grass marshes with willow on lowlands. There was a notable change in cover at the beginning of the Holocene when spruce forest spread to all upland surfaces except the highest ridges, and palu-dification in the lowlands resulted in the spread of bog and mire communities

Heritability and intrafamilial aggregation of arterial characteristics

BACKGROUND: We investigated the heritability and familial aggregation of various indexes of arterial stiffness and wave reflection and we partitioned the phenotypic correlation between these traits into shared genetic and environmental components. METHODS: Using a family-based population sample, we recruited 204 parents (mean age, 51.7 years) and 290 offspring (29.4 years) from the population in Cracow, Poland (62 families), Hechtel-Eksel, Belgium (36), and Pilsen, the Czech Republic (50). We measured peripheral pulse pressure (PPp) sphygmomanometrically at the brachial artery; central pulse pressure (PPc), the peripheral augmentation indexes (PAIxs) and central augmentation indexes (CAIxs) by applanation tonometry at the radial artery; and aortic pulse wave velocity (PWV) by tonometry or ultrasound. In multivariate-adjusted analyses, we used the ASSOC and PROC GENMOD procedures as implemented in SAGE and SAS, respectively. RESULTS: We found significant heritability for PAIx, CAIx, PPc and mean arterial pressure ranging from 0.37 to 0.41; P </= 0.0001. The method of intrafamilial concordance confirmed these results; intrafamilial correlation coefficients were significant for all arterial indexes (r >/= 0.12; P </= 0.02) with the exception of PPc (r = -0.007; P = 0.90) in parent-offspring pairs. The sib-sib correlations were also significant for CAIx (r = 0.22; P = 0.001). The genetic correlation between PWV and the other arterial indexes were significant (rhoG >/= 0.29; P < 0.0001). The corresponding environmental correlations were only significantly positive for PPp (rhoE = 0.10, P = 0.03). CONCLUSION: The observation of significant intrafamilial concordance and heritability of various indexes of arterial stiffness as well as the genetic correlations among arterial phenotypes strongly support the search for shared genetic determinants underlying these traits

Fire and canopy species composition in the Great Lakes-St. Lawrence forest of Témiscamingue, Québec

Large severe fires are typically rare in the northern hardwood forests of eastern North America, with estimated return intervals as high as 1400-4500 years. We investigated the history of large severe fires in western Qu

Arctic Holocene proxy climate database – New approaches to assessing geochronological accuracy and encoding climate variables

We present a systematic compilation of previously published Holocene proxy climate records from the Arctic. We identified 170 sites from north of 58° N latitude where proxy time series extend back at least to 6 cal ka (all ages in this article are in calendar years before present - BP), are resolved at submillennial scale (at least one value every 400 ± 200 years) and have age models constrained by at least one age every 3000 years. In addition to conventional metadata for each proxy record (location, proxy type, reference), we include two novel parameters that add functionality to the database. First, "climate interpretation" is a series of fields that logically describe the specific climate variable(s) represented by the proxy record. It encodes the proxy-climate relation reported by authors of the original studies into a structured format to facilitate comparison with climate model outputs. Second, "geochronology accuracy score" (chron score) is a numerical rating that reflects the overall accuracy of 14C-based age models from lake and marine sediments. Chron scores were calculated using the original author-reported 14C ages, which are included in this database. The database contains 320 records (some sites include multiple records) from six regions covering the circumpolar Arctic: Fennoscandia is the most densely sampled region (31% of the records), whereas only five records from the Russian Arctic met the criteria for inclusion. The database contains proxy records from lake sediment (60%), marine sediment (32%), glacier ice (5%), and other sources. Most (61%) reflect temperature (mainly summer warmth) and are primarily based on pollen, chironomid, or diatom assemblages. Many (15%) reflect some aspect of hydroclimate as inferred from changes in stable isotopes, pollen and diatom assemblages, humification index in peat, and changes in equilibrium-line altitude of glaciers. This comprehensive database can be used in future studies to investigate the spatio-temporal pattern of Arctic Holocene climate changes and their causes. The Arctic Holocene data set is available from NOAA Paleoclimatology. © Author(s) 2014

Range Expansion Drives Dispersal Evolution In An Equatorial Three-Species Symbiosis

A-09-14International audienceBackground Recurrent climatic oscillations have produced dramatic changes in species distributions. This process has been proposed to be a major evolutionary force, shaping many life history traits of species, and to govern global patterns of biodiversity at different scales. During range expansions selection may favor the evolution of higher dispersal, and symbiotic interactions may be affected. It has been argued that a weakness of climate fluctuation-driven range dynamics at equatorial latitudes has facilitated the persistence there of more specialized species and interactions. However, how much the biology and ecology of species is changed by range dynamics has seldom been investigated, particularly in equatorial regions. Methodology/Principal Findings We studied a three-species symbiosis endemic to coastal equatorial rainforests in Cameroon, where the impact of range dynamics is supposed to be limited, comprised of two species-specific obligate mutualists –an ant-plant and its protective ant– and a species-specific ant parasite of this mutualism. We combined analyses of within-species genetic diversity and of phenotypic variation in a transect at the southern range limit of this ant-plant system. All three species present congruent genetic signatures of recent gradual southward expansion, a result compatible with available regional paleoclimatic data. As predicted, this expansion has been accompanied by the evolution of more dispersive traits in the two ant species. In contrast, we detected no evidence of change in lifetime reproductive strategy in the tree, nor in its investment in food resources provided to its symbiotic ants. Conclusions/Significance Despite the decreasing investment in protective workers and the increasing investment in dispersing females by both the mutualistic and the parasitic ant species, there was no evidence of destabilization of the symbiosis at the colonization front. To our knowledge, we provide here the first evidence at equatorial latitudes that biological traits associated with dispersal are affected by the range expansion dynamics of a set of interacting species

Virtual Patients and Sensitivity Analysis of the Guyton Model of Blood Pressure Regulation: Towards Individualized Models of Whole-Body Physiology

Mathematical models that integrate multi-scale physiological data can offer insight into physiological and pathophysiological function, and may eventually assist in individualized predictive medicine. We present a methodology for performing systematic analyses of multi-parameter interactions in such complex, multi-scale models. Human physiology models are often based on or inspired by Arthur Guyton's whole-body circulatory regulation model. Despite the significance of this model, it has not been the subject of a systematic and comprehensive sensitivity study. Therefore, we use this model as a case study for our methodology. Our analysis of the Guyton model reveals how the multitude of model parameters combine to affect the model dynamics, and how interesting combinations of parameters may be identified. It also includes a “virtual population” from which “virtual individuals” can be chosen, on the basis of exhibiting conditions similar to those of a real-world patient. This lays the groundwork for using the Guyton model for in silico exploration of pathophysiological states and treatment strategies. The results presented here illustrate several potential uses for the entire dataset of sensitivity results and the “virtual individuals” that we have generated, which are included in the supplementary material. More generally, the presented methodology is applicable to modern, more complex multi-scale physiological models

“I know what a podcast Is” : post-Serial fiction and podcast media identity

This chapter seeks to assert that podcasts are a distinct media form and that although they might exhibit a ‘radioness’, they should be treated as a medium in their own right. This distinctiveness has been achieved over time through a process in which podcasters have asserted their own media identity. The chapter maps this development process using business models and a survey of practising podcasters, concluding that a new lens of ‘podcast studies’ is required to fully appreciate the nuances of this medium