Roads support the spread of invasive Asclepias syriaca in Austria
Asclepias syriaca (Asclepiadaceae, common milkweed) is a fast-growing perennial species native to North America. The species has invaded extensive areas within the EPPO region resulting in dense stands that can outcompete native plant species. In the European Union, the species is listed as an invasive alien species of Union concern. In Austria, A. syriaca is sporadically found growing in crop fields, vineyards or orchards, as well as along roadsides. The distribution of the species in Austria was evaluated by assessing occurrence records from several databases which contained records from 1990 until 2018. In addition, a detailed survey was undertaken along roadsides in the Marchfield region (Lower Austria) in Eastern Austria to assess abundance and distribution. In total, 82 records of A. syriaca were obtained for Austria. The species occurs primary in the east of the country (Vienna, Lower Austria). In western Austria records of the species were rare and restricted to a few isolated populations. In the Marchfield region, 78 populations of A. syriaca were recorded, where they were reasonably evenly distributed throughout the region. Populations were found along all road types and varied in size from individual plants to small populations of 25 plants.The probability of recording A. syriaca along local unpaved roads was significantly higher compared to regional paved or unpaved roads. In addition, there was a higher chance of finding A. syriaca along roads that had adjoining forest or grassland habitats compared to roads that bordered urban settlements. The results indicate that road networks can contribute to the spread of A. syriaca in the study area. In Austria, A. syriaca is considered in its early stages of invasion and it is predicted that the species will become more widespread in the future. Measures to mitigate the spread of the species should include roadside management including mowing regimes and the control of individuals in adjacent habitats.
The global distribution of A. syriaca has recently been updated in the EPPO Global database