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Buhler Y.,Institute for Snow and Avalanche Research | Adams M.S.,Austrian Research Center for Forests | Bosch R.,Swiss Federal Institute of forest | Stoffel A.,Institute for Snow and Avalanche Research
Cryosphere | Year: 2016

Detailed information on the spatiotemporal snow depth distribution is a crucial input for numerous applications in hydrology, climatology, ecology and avalanche research. Today, snow depth distribution is usually estimated by combining point measurements from weather stations or observers in the field with spatial interpolation algorithms. However, even a dense measurement network like the one in Switzerland, with more than one measurement station per 10 km2 on average, is not able to capture the large spatial variability of snow depth present in alpine terrain. Remote sensing methods, such as laser scanning or digital photogrammetry, have recently been successfully applied to map snow depth variability at local and regional scales. However, in most countries such data acquisition is costly if manned airplanes are involved. The effectiveness of ground-based measurements on the other hand is often hindered by occlusions, due to the complex terrain or acute viewing angles. In this paper, we investigate the application of unmanned aerial systems (UASs), in combination with structure-from-motion photogrammetry, to map snow depth distribution. Compared to manual measurements, such systems are relatively cost-effective and can be applied very flexibly to cover terrain not accessible from the ground. In this study, we map snow depth at two different locations: (a) a sheltered location at the bottom of the Fluëla valley (1900ma.s.l.) and (b) an exposed location on a peak (2500ma.s.l.) in the ski resort Jakobshorn, both in the vicinity of Davos, Switzerland. At the first test site, we monitor the ablation on three different dates. We validate the photogrammetric snow depth maps using simultaneously acquired manual snow depth measurements. The resulting snow depth values have a root mean square error (RMSE) of less than 0.07 to 0.15m on meadows and rocks and a RMSE of less than 0.30m on sections covered by bushes or tall grass, compared to manual probe measurements. This new measurement technology opens the door for efficient, flexible, repeatable and cost-effective snow depth monitoring over areas of several hectares for various applications, if the national and regional regulations permit the application of UASs. © 2016 Author(s).

Sovilla B.,WSL Institute for Snow and Avalanche Research SLF | Faug T.,IRSTEA | Kohler A.,WSL Institute for Snow and Avalanche Research SLF | Baroudi D.,Aalto University | And 2 more authors.
Cold Regions Science and Technology | Year: 2016

Low-speed wet avalanches exert hydrostatic forces on structures that are flow-depth dependent. However, the pressure amplification experienced by smaller structures has not been quantified previously. In particular, recent wet avalanche pressure measurements, performed with small cells at the "Vallée de la Sionne" test site, indicate significantly higher pressures than those considered by engineering guidelines and common practice rules based only on the contribution of inertial forces. In order to gain a deeper understanding and investigate the relevance of these measurements for structural design, we analyzed data measured on obstacles of different shapes and dimensions. The pressure measured on a 1 m2 pressure plate was, on average, 1.8 times smaller than the pressure measured on a 0.008 m2 piezoelectric cell installed on a 0.60 m wide pylon and 2.9 times smaller than the pressure measured on a 0.0125 m2 cantilever sensor extending freely into the avalanche flow. Further, avalanches characterized by a gravitational flow regime exerted pressures that increased linearly with avalanche depth. For Froude numbers larger than 1, an additional square-velocity dependent contribution could not be neglected. The pressure variations encountered by the different obstacles could be explained quantitatively with a granular force model, that assumes the formation of a mobilized volume of snow granules extending from the obstacle upstream whose dimensions depend on the incoming flow depth and the obstacle width. This mobilized volume is associated with the formation of a network of gravity-loaded grain-grain contacts, also called granular force chains, which densifies in front of the obstacle, producing force amplification. Our results underscore the fundamental influence of the dimensions of both the sensor and the obstacle on pressures in the gravitational flow regime and may help to improve rules for structural design. © 2016 The Authors.

Paule J.,Senckenberg Institute | Kolar F.,University of Oslo | Kolar F.,Charles University | Kolar F.,Academy of Sciences of the Czech Republic | And 2 more authors.
Preslia | Year: 2015

The link between polyploidy and the disjunct arctic-alpine European distribution of Potentilla crantzii was studied with particular reference to the role of serpentine habitats. Flow cytometry, AFLPs and cpDNA sequencing provided insights into ploidy level variation and the genetic structure of European populations. We recorded a ploidy differentiated arctic-alpine disjunction with tetraploids limited to the central- and southern-European mountain chains and hexaploids dominating in the Subarctic. Two lowland serpentine populations in the Czech Republic and Austria exhibited contrasting genetic patterns suggesting different evolutionary histories, with the tetraploid Czech population showing a conspicuously high genetic diversity. Finally, our genetic and cytological data did not support a distinct taxonomic status for the serpentine populations that were traditionally differentiated as P. crantzii subsp. serpentini.

Hoyer-Tomiczek U.,Austrian Research Center for Forests | Sauseng G.,Sonnenweg 1 | Hoch G.,Austrian Research Center for Forests
EPPO Bulletin | Year: 2016

Surveillance for the Asian longhorn beetle, Anoplophora glabripennis, currently depends on visual inspection. As one complementary method, dogs have been trained and employed for the detection of A. glabripennis since 2009. In this study, two sets of experiments in double-blind trials were carried out to quantify the sensitivity of the dog detection method using 10 dogs in the first set and 14 dogs in the second. All experiments used the same basic set-up of 2 positive and 6 negative samples presented in random order. In the first series, A. glabripennis scent material (frass, a living larva or infested wood plus a living larva) was placed in hollow building blocks invisible to dogs and handlers. The experiments had an overall sensitivity of 85-93% (correct positives of all positives) and specificity of 79-94% (correct negatives of all negatives). The second series tested more realistic but also standardized situations: A. glabripennis frass and wood shavings were hidden in ground vegetation at the base of young poplar trees in a plantation, in tubes at a height of 1.8 m on these poplar trees and in crevices on old trees in an orchard at a height of about 1.8 m, respectively. These experiments had an overall sensitivity of 75-88% and a specificity of 85-96%. © 2016 The Authors.

Stolting K.N.,University of Fribourg | Paris M.,University of Fribourg | Meier C.,University of Fribourg | Heinze B.,Austrian Research Center for Forests | And 3 more authors.
New Phytologist | Year: 2015

Studying the divergence continuum in plants is relevant to fundamental and applied biology because of the potential to reveal functionally important genetic variation. In this context, whole-genome sequencing (WGS) provides the necessary rigour for uncovering footprints of selection. We resequenced populations of two divergent phylogeographic lineages of Populus alba (n = 48), thoroughly characterized by microsatellites (n = 317), and scanned their genomes for regions of unusually high allelic differentiation and reduced diversity using > 1.7 million single nucleotide polymorphisms (SNPs) from WGS. Results were confirmed by Sanger sequencing. On average, 9134 high-differentiation (≥ 4 standard deviations) outlier SNPs were uncovered between populations, 848 of which were shared by ≥ three replicate comparisons. Annotation revealed that 545 of these were located in 437 predicted genes. Twelve percent of differentiation outlier genome regions exhibited significantly reduced genetic diversity. Gene ontology (GO) searches were successful for 327 high-differentiation genes, and these were enriched for 63 GO terms. Our results provide a snapshot of the roles of 'hard selective sweeps' vs divergent selection of standing genetic variation in distinct postglacial recolonization lineages of P. alba. Thus, this study adds to our understanding of the mechanisms responsible for the origin of functionally relevant variation in temperate trees. © 2015 New Phytologist Trust.

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