The invasion of Austria by the alien vascular plant Ambrosia artemisiifolia (Asteraceae) is analysed in detail, based on a survey of available records. In total, 697 records were collated. The first record for Austria is a herbarium specimen collected in 1883. Up to the end of the 1940s, records were rare and only of casual populations resulting from long-distance dispersal. Since the 1950s, the number of records has increased exponentially, and more than one third of all records (242) were collected in the last 5-year period (2001–2005) included in the survey. The first naturalized population was recorded in 1952, nearly 70 years after the first record of a casual population. Recently, the number of naturalized populations increased considerably faster than that of casual populations. Several pathways (contaminated crops and bird seed, agricultural machines, transport of soil) have contributed to the high levels of propagule pressure and this successful invasion. Ambrosia artemisiifolia has undergone a niche expansion during the invasion process. Up to 1950, most records were from sites along railway routes, whereas in the period 1950–1974 itwas mostly ruderal habitats, not associated with traffic infrastructure, which were colonized. Since the 1970s, records from roadsides have increased strongly and now dominate. Fields were colonized first in the 1970s and since then have gained in importance. The distribution of naturalized populations was related to environmental and climatic variables by means of a generalized linear model. Their distribution in Austria is closely related to temperature. Landscape variables, describing aspects of habitat availability (topography, land use, major street density) also significantly explain the current distribution of A. artemisiifolia. Suitable habitats currently occur mainly in the eastern and southeastern lowlands. We conclude that global warming will disproportionally enhance the invasion success of A. artemisiifolia in Austria, even if there is only a slight increase in temperature, as significant areas of agricultural land in Austria are currently only slightly too cool for A. artemisiifolia. The widespread occurrence of this species will have serious consequences for human health and agriculture.
Stability conditions in a wider surrounding of the rock castle Drábské Světničky (Drábské Rooms) near the town of Mnichovo Hradiště were investigated. The area which has been intensively disturbed by large old as well as present slope movements is located in the north-western part of Příhrazy Platform. Solid, thick bedded sandstones, well resistant to weathering, are lying on claystones apt to plastic deformations. Marginal sandstone blocks separate, move down on the slope and sink into the plastic bedrock. As a result, block fields with many crevasses develop. In rock walls that separate individual blocks, rockfalls originate and central, as well as lower parts of the slopes develop large landslides. A zone comprising up to 400 m wide rim of the high and exposed platform has been subject to a process of loosening. A local group of tower-like sandstone blocks was used in the 15th century to build a small rock castle called Drábské Světničky. An extensive landslide that destroyed a substantial part of the village of Dneboh in June 1926, reached in its separating zone up to the toe of marginal rock towers belonging to the complex of Drábské Sv ě tni č ky with the result of local movement activation. Marginal zones of the flat land behind display fresh linear, as well as oval depressions and sinks. Fissure and pseudocarst caves develop. Present activity of the movements has been evidenced by dilatometric measurements on two selected rock objects where movement rates reached 1 to 2 mm per year in average., Jan Rybář, Josef Stemberk and Filip Hartvich., and Obsahuje bibliografické odkazy
The Laplacian spread of a graph is defined as the difference between the largest and second smallest eigenvalues of the Laplacian matrix of the graph. In this paper, bounds are obtained for the Laplacian spread of graphs. By the Laplacian spread, several upper bounds of the Nordhaus-Gaddum type of Laplacian eigenvalues are improved. Some operations on Laplacian spread are presented. Connected $c$-cyclic graphs with $n$ vertices and Laplacian spread $n-1$ are discussed.