Buhler Y.,WSL Institute for Snow and Avalanche Research SLF |
Adams M.S.,Austrian Research Center for Forests |
Stoffel A.,WSL Institute for Snow and Avalanche Research SLF |
Boesch R.,Swiss Federal Institute of forest
International Journal of Remote Sensing | Year: 2017
Operating unmanned aerial systems (UAS) to record imagery of alpine snow cover for photogrammetric applications is challenging due to topographic and meteorological conditions. Furthermore, the homogenous snow surface encumbers the automated detection of matching points, which are required for generating accurate digital surface models (DSMs). On the other hand, there is rising demand for high spatial resolution snow depth and snow surface-type mapping as well as snow avalanche documentation. UAS have the potential to enable flexible, timely, and cost-efficient data acquisition, even in poorly accessible alpine terrain. This could be a major step forward for many applications in snow hydrology, avalanche research, mitigation measure planning, hazard zonation, and alpine ecology investigations. In this study, we investigate the applicability and performance of UAS-based structure-from-motion (SfM) photogrammetry on very homogenous snow surfaces, under suboptimal illumination conditions, at two alpine test sites in Tschuggen (2000 m a.s.l.) close to Davos, Switzerland, and Lizum (2000 m a.s.l.) near Innsbruck, Austria. We discuss the topographic and meteorological challenges for flying UAS missions in high-alpine terrain. Additionally, we compare DSMs calculated from the imagery acquired in the visual (VIS, λ = 400–700 nm) and near-infrared (NIR, λ = 700–830 nm) parts of the electromagnetic spectrum. We evaluate the resulting DSMs qualitatively and quantitatively by applying: a) differential Global Navigation Satellite System (GNSS) measurements at the Swiss test site, with an expected accuracy better than 0.1 m within x, y, and z directions; b) terrestrial laser scanning (TLS) at the Austrian test site, with an expected accuracy of ± 0.025 m (1σ), along with a distance-dependent error. The results of this study reveal the potential and limitations of UAS-based SfM photogrammetry for applications on snow-covered, alpine terrain in general and in particular the benefit of NIR imagery on the accuracy and precision of the results. © 2017 Informa UK Limited, trading as Taylor & Francis Group
Mergili M.,University of Natural Resources and Life Sciences, Vienna |
Mergili M.,University of Vienna |
Fischer J.-T.,Austrian Research Center for Forests |
Krenn J.,University of Natural Resources and Life Sciences, Vienna |
Pudasaini S.P.,University of Bonn
Geoscientific Model Development | Year: 2017
R.avaflow represents an innovative open-source computational tool for routing rapid mass flows, avalanches, or process chains from a defined release area down an arbitrary topography to a deposition area. In contrast to most existing computational tools, r.avaflow (i) employs a two-phase, interacting solid and fluid mixture model (Pudasaini, 2012); (ii) is suitable for modelling more or less complex process chains and interactions; (iii) explicitly considers both entrainment and stopping with deposition, i.e. The change of the basal topography; (iv) allows for the definition of multiple release masses, and/or hydrographs; and (v) serves with built-in functionalities for validation, parameter optimization, and sensitivity analysis. r.avaflow is freely available as a raster module of the GRASS GIS software, employing the programming languages Python and C along with the statistical software R. We exemplify the functionalities of r.avaflow by means of two sets of computational experiments: (1) generic process chains consisting in bulk mass and hydrograph release into a reservoir with entrainment of the dam and impact downstream; (2) the prehistoric Acheron rock avalanche, New Zealand. The simulation results are generally plausible for (1) and, after the optimization of two key parameters, reasonably in line with the corresponding observations for (2). However, we identify some potential to enhance the analytic and numerical concepts. Further, thorough parameter studies will be necessary in order to make r.avaflow fit for reliable forward simulations of possible future mass flow events. © Author(s) 2017.
Bressler S.,University of Vienna |
Klatte-Asselmeyer V.,University of Vienna |
Fischer A.,University of Vienna |
Paule J.,Senckenberg Institute |
And 2 more authors.
Preslia | Year: 2017
Polyploidy, aneuploidy and changein DNA content of monoploid genomesor chromosomes are the principal causes of the variation in genome size. We studied these phenomena in central-European populations of the Valeriana officinalis complex in order to identify mechanisms or forces driving its evolution. The complex comprises di-, tetra- and octoploid morphologically defined so-called taxonomic "types". Within the study area there are also intermediate "transitional types" the existence of which hampers the application of traditional taxonomic concepts. We thus chose AFLP genotyping and admixture analyses to identify the genetic structuring of the material studied. Di-(2x), tetra-(4x) and octoploidy (8x) were confirmed as major ploidy levels. Major genetic clusters roughly corresponded to these ploidy levels (for K = 2:2x- and 8x-clusters, for K = 4 with nearly identical probability: 2x-, 4x-, 8x- and unspecific clusters were identified), which further more significantly differed from each other in monoploid absolute genome size (mean 1Cx for 2x = 1.48 pg, 4x 1.29 pg, 8x 1.10 pg). Several individuals of all ploidy levels were admixed, particularly tetraploids. Relative genome size (the sample: standard DAPI fluorescence) was positively correlated with the proportion of the diploid genetic cluster shared by the tetraploids, indicating that hybridization caused the variation in genome size. This result is in accordance with the significant negative correlation of the genome size of tetraploids with their geographic distance to the diploids. However, remarkable intra-ploidy variation in relative genome size was recorded for all ploidy levels (1.14-fold in diploids, 1.28-fold in tetraploids, 1.19-fold in octoploids). We identified aneuploidy as an additional source of variation in genome size in the di- and tetraploids. The contribution of extra chromosomes to absolute genome size exceeded the observed variation within euploids in the diploids, whereas it was included in the regular variability in genome size recorded for the eutetraploids. Variation in monoploid genome size was recorded in polyploids but not in diploids, indicating that polyploids experienced higher dynamics in the evolution of their genomes. Finally, 38.0-63.2% of the total intra-ploidy variation in relative genome size occurred within populations. In conclusion, the Valeriana officinalis complex provides an example of variation in genome size due to four principal evolutionary forces: polyploidization, change in chromosome number and in DNA content of chromosomes and (secondarily) hybridization, but their relative importance differed among ploidy levels. Although the stability in the size of the monoploid genome in species is considered to be the standard case, we found great variability within populations suggesting that genome size is variable even within narrowly defined taxa.
Dobes C.,Austrian Research Center for Forests |
Konrad H.,Austrian Research Center for Forests |
Geburek T.,Austrian Research Center for Forests
Diversity | Year: 2017
Habitat fragmentation threatens the maintenance of genetic diversity of affected populations. Assessment of the risks associated with habitat fragmentation is a big challenge as the change in population genetic diversity is a dynamic process, often acting over long time periods and depending on various characteristics pertaining to both species (life history traits) and their populations (extrinsic characteristics). With this survey, we provide an introductory overview for persons who have to make or are interested in making predictions about the fate of forest-dwelling plant populations which have recently become fragmented and isolated from their main occurrences. We provide a concise introduction to the field of population genetics focusing on terms, processes and phenomena relevant to the maintenance of genetic diversity and vitality of plant populations. In particular the antagonistic effects of gene flow and random genetic drift are covered. A special chapter is devoted to Central European tree species (including the Carpathians) which we treat in detail with reference to an extensive literature survey on population genetic studies assembled from the whole of Europe. We further provide an overview of the population biology of associated understorey species. We conclude with recommended steps to be taken for the evaluation of potential perils of habitat fragmentation or population thinning for the genetics of tree populations. The complexity of effects exerted by life history traits and extrinsic characteristics of populations suggest population genetic development is strongly situation dependent. Therefore, we recommend following a case-by-case approach ideally supported by computer simulations to predict future population genetic development of both trees and associated understorey species. © 2017 by the authors.
Fischer J.-T.,Austrian Research Center for Forests |
Kofler A.,Austrian Research Center for Forests |
Fellin W.,University of Innsbruck |
Granig M.,Snow and Avalanche Center |
Kleemayr K.,Austrian Research Center for Forests
Journal of Glaciology | Year: 2015
Snow avalanche simulation software is a commonly used tool for hazard estimation and mitigation planning. In this study a depth-averaged flow model, combining a simple entrainment and friction relation, is implemented in the software SamosAT. Computational results strongly depend on the simulation input, in particular on the employed model parameters. A long-standing problem is to quantify the influence of these parameters on the simulation results. We present a new multivariate optimization approach for avalanche simulation in three-dimensional terrain. The method takes into account the entire physically relevant range of the two friction parameters (Coulomb friction, turbulent drag) and one entrainment parameter. These three flow model parameters are scrutinized with respect to six optimization variables (runout, matched and exceeded affected area, maximum velocity, average deposition depth and mass growth). The approach is applied to a documented extreme avalanche event, recorded in St Anton, Austria. The final results provide adjusted parameter distributions optimizing the simulation-observation correspondence. At the same time, the degree of parameter-variable correspondence is determined. We show that the specification of optimal values for certain model parameters is near-impossible, if corresponding optimization variables are neglected or unavailable.
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.
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.
Jansen S.,Austrian Research Center for Forests |
Geburek T.,Austrian Research Center for Forests
Forest Ecology and Management | Year: 2016
For the first time we have reviewed historic data throughout Europe to assess how European larch has been artificially distributed from the 17th until the mid-20th century. Over this period, larch genetic resources have been translocated with varying intensity. Especially Alpine plant material was transferred outside the native range across Europe, while genetic resources originating from the Sudetes were mainly spread to northeastern Germany, northwestern Poland, and to the Sudetes outside of the species’ native range. Polish larch was mainly translocated within Poland. Genetic resources from the Carpathian Mountains (Tatras, eastern and southern Carpathians) were not used for long-distance transfer. While native larch populations in the Alps and in Poland were not significantly affected by allochthonous plant material, the native gene pool of larch in the Sudetes and Carpathians Mountains was strongly altered by Alpine plant material. We provide several maps illustrating these translocations over time and space. These findings are of special importance, as genetic data tracking the original seed source are presently not available. © 2016 Elsevier B.V.
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).
PubMed | University of West Hungary, University of Salerno, Austrian Research Center for Forests and University of Fribourg
Type: Journal Article | Journal: The 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.