Control of invasive Ailanthus altissima in the Danube floodplain forests in Bratislava using chemical and biological agents

Abstract

Ailanthus altissima is an Asian tree species that has become invasive on all continents except Antarctica. In Europe, it frequently invades native floodplain forest habitats. Three methods of control are known presently, namely mechanical, chemical, and biological. As each method has its advantages and disadvantages, we compared chemical control using glyphosate with biological control using the Verticillium nonalfalfae isolate Vert56 in the protected area of the Danube floodplain forests belonging to the municipality of Bratislava, Slovakia. Furthermore, we modelled the potential distribution of A. altissima in Bratislava and searched for factors that influenced its distribution. Our results showed that although chemical control is more effective in inducing mortality of inoculated individuals, biological control additionally allows the elimination of individuals growing in the vicinity of inoculated individuals. Results also suggest that, in the situation where the Verticillium wilt becomes chronic, microclimatic conditions may play a significant role in biological control, as individuals growing in dry, sunny sites showed a higher percentage of mortality compared to individuals growing in moist, shaded forest sites. According to the species distribution model, A. altissima is equally likely to exist in urban areas and floodplain forests, as evidenced by the same probability of species occurrence. A. altissima is spreading into Bratislava´s floodplain forests, primarily around roads and railway tracks, but it also benefits from increased light conditions on forest regeneration sites caused by deforestation.