The giant hogweed on the Alps: niche dynamics of a burning invasive alien plant across the alpine region

Raffaele De Matteis ¹

Univeristà degli Studi di Milano-Bicocca ¹

Giant hogweed (Heracleum mantegazzianum Sommier & Levier; Apiaceae) is an invasive plant, native to the Caucasus and introduce to Europe in the 19th century, where it has spread thanks to its adaptive traits and frequent cultivation. It can have negative impacts on ecosystems and even public health, due to severe burnings caused by its toxic sap. Therefore, its management is mandatory in the EU (EU regulation n.1143/2014). Understanding its ecology in Europe should be paramount for such purpose, but studies are few. For example, there is a lack of knowledge for the Alps, an area where H. mantegazzianum is not evenly distributed, with sharp differences going southward and westward. In this study, we investigate the reasons of such differences, to understand if they are mainly due to climatic or environmental limits. We analysed the ecological niche of the species and its dynamics across different sectors: north and south, east and west. A PCA-based method was used to test the differentiation of niches in ecological space, defined by climatic and environmental terms. Niche dynamics across the sectors were described following the COUE framework. The analyses showed differences and shifts southward and westward, mainly regarding climate. Climatic factors explain most variance along the PCs, especially air and soil winter temperatures, together with summer and winter rainfalls. Focusing on climatic niche dynamics between north and south, the niches are mostly stable, but they do not fully overlap, and they are not similar. In the south, the species shifts to conditions absent in the north, with lower annual rainfall and warmer winters. For the dynamics from east to west, the niche stability is low as the alien expands to new conditions westward, with drier, warmer winters. Following the shifts, the analyses indicate that H. mantegazzianum should occupy warmer, drier conditions in south-western Alps. There, the species is less spread than elsewhere on the chain, likely due to unsuitable novel climatic conditions. This may be caused by a lack of sufficiently cold and wet winters, needed to break seed dormancy. Conversely, environmental niche dynamics are highly stable, with irrelevant shifts: the species does not occupy sites with novel soil or land cover characteristics anywhere. Even if they have a marginal role, the variance determined by such factors is mostly explained by urban cover, soil organic carbon and pH. In conclusion, differences in the distribution of H. mantegazzianum across the Alps are mainly due to climate. Even if this analysis would require further small-scale integrations, its results should be considered in the management of the species in the EU.

Main author career stage: Master student

Contribution type: Talk

First choice session: 3. Biodiversity and global change

Second choice session: 2. Ecology