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Zieher T.,University of Innsbruck | Gruber F.E.,University of Innsbruck | Rutzinger M.,University of Innsbruck | Meissl G.,University of Innsbruck | And 2 more authors.
Landslides and Engineered Slopes. Experience, Theory and Practice | Year: 2016

Shallow landslides are an abundant phenomenon in mountain regions. Since these processes often endanger settlements and infrastructure it is important to estimate their spatial occurrence. Hence, various modelling techniques for the area-wide assessment of shallow landslide susceptibility are applied (i.e. heuristic, statistically- and physically-based approaches). Amongst these, statistically-based approaches are based on the assumption that factors promoting landslides in the past will also facilitate landsliding in future. Therefore a shallow landslide inventory for the area of interest including sufficient observations for training and validation of the model as well as a high-quality digital terrain model are prerequisites. With the help of a multi-annual shallow landslide inventory and derivatives of two airborne laser scanning campaigns (i) the optimal spatial resolution of the digital terrain model, (ii) the ideal training-to-validation split and (iii) the minimal number of observed landslides required for the assessment of shallow landslide susceptibility using logistic regression are investigated. Predictors are based on the digital terrain models and comprise slope angle, aspect, minimum and maximum curvature, slope length and topographic wetness index. The objectives are discussed for three study areas in Vorarlberg, Austria. Results of the modelling experiments show best performances using a digital terrain model with a spatial resolution of 5 m and a training-to-validation split of 3:7. Regarding the inventory size at least 150 mapped landslides were necessary to achieve acceptable results. However, it is recommended that at least 400 observed landslide locations at a minimum landslide density of 3 landslides/km2 are considered for the statistically-based assessment of shallow landslide susceptibility. © 2016 Associazione Geotecnica Italiana, Rome, Italy.

Zieher T.,University of Innbruck | Perzl F.,Austrian Research and Training Center for Forests | Rossel M.,Austrian Research and Training Center for Forests | Rutzinger M.,University of Innbruck | And 4 more authors.
Geomorphology | Year: 2016

Geomorphological landslide inventories provide crucial input data for any study on the assessment of landslide susceptibility, hazard or risk. Several approaches for assessing landslide susceptibility have been proposed to identify areas particularly vulnerable to this natural hazard. What they have in common is the need for data of observed landslides. Therefore the first step of any study on landslide susceptibility is usually the compilation of a geomorphological landslide inventory using a geographical information system. Recent research has proved the feasibility of orthophoto interpretation for the preparation of an inventory aimed at the delineation of landslides with the use of distinctive signs in the imagery data. In this study a multi-annual landslide inventory focusing on shallow landslides (i.e. translational soil slides of 0-2 m in depth) was compiled for two study areas in Vorarlberg (Austria) from the interpretation of nine orthophoto series. In addition, derivatives of two generations of airborne laser scanning data aided the mapping procedure. Landslide scar areas were delineated on the basis of a high-resolution differential digital terrain model. The derivation of landslide volumes, depths and depth-to-length ratios are discussed. Results show that most mapped landslides meet the definition of a shallow landslide. The inventory therefore provides the data basis for the assessment of shallow landslide susceptibility and allows for the application of various modelling techniques. © 2016 Elsevier B.V.

Martin-Garcia J.,University of Valladolid | Solla A.,University of Extremadura | Corcobado T.,University of Extremadura | Corcobado T.,Austrian Research and Training Center for Forests | And 3 more authors.
Forest Pathology | Year: 2015

The influence of temperature on germination of Quercus ilex acorns in Phytophthora infested soils was quantified for the first time. Radicle damage and mortality of Q. ilex seeds germinating at 17, 20, 23 and 26°C in Phytophthora cinnamomi, P. gonapodyides, P. quercina and P. psychrophila infested soils were assessed and related to in vitro mycelium growth of the same isolates of the pathogens. The optimum growth temperatures of isolates of P. cinnamomi, P. gonapodyides, P. quercina and P. psychrophila were 20-23, 23-26, 20-23 and 20°C, respectively. At 17 and 20°C, all four Phytophthora species caused 100% acorn mortality, whereas at 26°C, acorn mortality was 100, 10, 25 and 0% in P. cinnamomi, P. gonapodyides, P. quercina and P. psychrophila infested soils, respectively. At 23°C, P. cinnamomi and P. gonapodyides reduced acorn radicle length more than P. quercina and P. psychrophila, whereas at 26°C, only P. cinnamomi caused further reduction in radicle length. The higher susceptibility of germinating acorns in comparison to seedlings reported in the literature indicates age-related susceptibility of Q. ilex to Phytophthora. The seedling/pathogen growth ratio was inversely related to the reduction in radicle length at different temperatures (Radj2 = 0.84, p < 0.0001), suggesting that rapid germination may allow seedlings to escape from infection. Increasing temperatures had different effects on damage to acorns depending on the pathogen present in the soil, indicating that Phytophthora species × temperature interactions determined Q. ilex germination. The effects of temperature on the impacts of Phytophthora species based on climate change predictions for Mediterranean countries are discussed. © 2014 Blackwell Verlag GmbH.

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