Die viatische Migration einiger neophytischer Pflanzensippen am Beispiel norddeutscher Autobahnen
Motorways can be migration lines for neophytic plant species. The median strips inbetween the roadways are not as often influenced by mowing as the outer verges. In consequence normally there is no turf restraining tall dicotyles from germinating and growing up. Seeds can be transported along the road directly by means of car tyres or indirectly by impact of air perturbation caused by vehicles. In northern Germany several motorways were investigated with respect to Stands ofAtriplex micrantha LEDEB., Atriplex oblongifolia W. & K., Atriplex sagittata BORKH. and Senecio inaequidens DC. Whereas Atriplex micrantha has been resident at ruderal locations in southwestern Germany for some decades it was only scarcely recorded in northern Germany so far. The investigation shows it is frequent now at motorway locations in southern and central Lower Saxony, Northrhine-Westphalia, Saxony-Anhalt and Brandenburg. As it is meanwhile also frequently to be found in the Elbe and Saale valley, seeds may possibly have been spread from there into the motorway sites äs well. Atriplex oblongifolia, long since resident especially in the eastern and southwestern countries but rare in Lower Saxony, also spreads along motorways in Lower Saxony now. Atriplex sagittata, archaeophyte in the investigated region, is still the most frequent of the three mapped Atriplex species. Senecio inaequidens, to a great extent spreading in regions of atlantic climate and familiär in the Hanover area for about two decades, was frequently found in 1995 also on the median strips of the motorway A 2 between Hanover and Berlin, thus invading a region influenced by fairly subcontinental climate. Whereas all of the above plant species seem to have covered long distances on the named roadside habitats in the course of only some years and often build up large populations there, they have not considerably penetrated into the surrounding areas yet. Points of diaspore transfer are bridges over roads and rivers äs well äs grassy slopes.