Abstract :
[en] Cotoneaster horizontalis DECAISNE, a Rosaceae coming from Asia, was introduced in Belgium as an ornamental species. Different sides of the invasion were studied, from the distribution of the species and the invasion status, the impacts, to management methods.
To describe the invasion status, information was gathered about the occurrence and the distribution of the species in Belgium by compiling various databases. The naturalization status in calcareous grasslands, high-value habitats recognized as biodiversity hotspots, was assessed. Occurrence, population status, preferred habitats, invaded communities, growth rate and fruiting capacity were characterized. Once naturalization established, we investigated its impacts on calcareous grasslands communities, individual species and pollinators.
C. horizontalis occurred in seven of the nine studied calcareous grasslands, with densities from 0.34 to 10 individuals/ha. In the most invaded sites, an ongoing colonization process was suggested by a high proportion of small individuals. Moreover, 3-year-old individuals already showed fruiting capacities. Germination rate reached about 30%.
Significant impacts on habitat structure and vegetation were showed. Community structure and composition changes were demonstrated in invaded sites by decreasing species richness and diversity.
As calcareous grasslands are priority Natura2000 habitats, measures must be taken to control the spread of C. horizontalis. For this purpose, we performed management tests to identify the most efficient techniques that would help the restoration of calcareous grasslands. Both mechanical and chemical management techniques were tested. Methods choice was driven by the environmental constraints of calcareous grasslands, which require highly selective techniques, and by species characteristics. Tested methods were cuttings, stump burning, spraying, cutting plus glyphosate application on stump and glyphosate application on stem basis. Efficiency, cost, feasibility and side-effects on ecosystems were estimated. Management tests are still ongoing but some results have already been drawn: spraying and single cutting are not efficient, the last one generating production of numerous sprouts.
Finding the best management method will not be sufficient to stop the invasion. C. horizontalis is still present in 53% of the sale catalogs of horticulturists in Southern Belgium. As long as the species is used in the vicinity of calcareous grasslands, propagules are continuously provided, jeoparding management actions.
