Conference Agenda

The number of alien species has steadily increased over past decades and centuries leading to now >37,000 recorded alien species worldwide. As shown in the recent IPBES assessment on invasive alien species, this can have negative consequences for nature and human well-being. The spread of species, and therefore also their current distribution, is highly uneven across the globe with marked hot spots in economically productive countries, and these hot spots remained rather stable over recent centuries. I will give an overview about the long-term trends of alien species numbers, their distributions and major drivers. I will also provide an overview of knowledge gaps and their influences on our understanding of the observed patterns. As the major drivers of biological invasions will accelerate in their intensities, the number of alien species and invasive alien species are expected to rise likewise in the future. I will give an overview of the projected distribution of alien species and will end the presentation with options to mitigate the spread of species.

Having 40 plant species registered on a list of prohibited species based on a scientific risk assessment is all very nice, but how does this translate into action? How can we prevent the entry of these plants? How can we guarantee that they are no longer in trade and how can we prevent further spread of those species already established? How to identify them, as they do not always come with a name tag or are often, willingly or not, mislabelled. What tools do we have to identify them at the border, when they arrive as a commodity or contaminant, or at sale points, either via e-commerce or in a shop. How to tell them apart from congeners and look-alikes. Once listed we realize that there can be quite some taxonomical confusion, as has been seen with Gunnera, Myriophyllum, Salvinia and Pennisetum to name a few. In addition to the tools to prevent entry, we need an early warning system to report any sightings in natural areas. If despite all our efforts to keep these invasive plants out, they do arrive in natural areas, what options do we have to eradicate or control them.

Invasive species are among the main global drivers of biodiversity loss, posing major challenges to nature conservation in the network of protected areas. Assessing the risk posed by invasive species through different frameworks, at different spatial scales and under different protection regimes represents an attempt to bridge the gap between theory and practice in conservation planning. This can help to identify site, management, monitoring, and control priorities specific to both established and newly arriving species. This synthesis discusses emerging insights on the identification of threats posed by invasive plants, and the most important drivers shaping invasive plants' occurrence inside protected areas, such as abiotic filters, key information to define appropriate strategies for prevention and monitoring of uninvaded areas. Local authorities and managers of protected areas should pay particular attention to the presence of communication infrastructures as well as to the local landscape and land use changes which may have crucial roles in promoting or preventing plant invasions. The staff of protected areas should conduct periodical field surveys on areas with high invasion risk to record the presence of non-native species and their invasion stage.

Invasive trees are a major threat to biodiversity and functioning of forests. Most previous studies focused on comparing invaded and non-invaded sites, while few studies considered invader quantity as driver of impacts or dispersal ability. Here we present patterns of dispersal and impacts of model invasive trees: Prunus serotina, Quercus rubra, and Robinia pseudoacacia. We revealed strong dependence of the invader’s natural regeneration density on quantity of parental trees. This relationship was the strongest for Q. rubra, producing large seeds, and the weakest for R. pseudoacacia, producing light, wind-dispersed seeds. Quantity of parental trees also negatively affected seedling survival at one year since germination. We also found that quantity of invaders affected natural regeneration of alien and native tree species, as well as understory species composition and biodiversity. In contrast, we did not confirm any impacts of invaders on aboveground biomass increments of native trees. We conclude that management of invasive trees should account for invader quantity, aiming to develop thresholds of negative impacts that can be mitigated and/or accepted in case-specific management scenarios. Such an approach would allow for prioritization of silvicultural treatments on sites with high conservation values and support optimization of conservation management in forests.

Transportation and reuse of soils can introduce invasive alien plants (IAPs) to new regions. Steam as an alternative to chemical fumigation, may allow contaminated soil to be disinfected. In 2021 and 2022, a dose-response experiment was performed. Seeds of selected IAPs incorporated in three different soils were exposed to steam treatment heating the soils to a maximum of 60-99°C before steaming stopped. Seeds were kept in the heated soil for three more minutes before being removed from the soil. Results showed that the soils were different in terms of reaching target temperatures, however, killing of the seeds was not affected by soil type. For each species, the response (seed germination percentage) to the maximum soil temperatures was described by a log-logistic dose-response model. The soil temperature required to reduce seed germination by 90% (ED90) was about 67°C for Heracleum mantegazzianum, 70°C for Impatiens glandulifera, 75°C for Avena fatua (both Polish and Norwegian population), 76°C for Echinochloa crus-galli (Polish population), 79°C for E. crus-galli (Norwegian population), 78°C for Solidago canadensis, and 105°C for Lupinus polyphyllus. Overall results showed promising control levels of IAP propagules in contaminated soils, except for L. polyphyllus. Steaming measures, therefore, should be adapted based on target species.