Public perceptions about the invasive pampas grass, Cortaderia selloana: a case study of environmentally conscious citizens in Southern Europe.

Cortaderia selloana (pampas grass), native to South America, is a widespread invasive plant in several regions of the World, including the south of the Atlantic Arc (Europe), where it has been used as an ornamental species. Citizens may help to spread it, e.g., planting it in their gardens, but on the other hand, when they are aware of its invasiveness, can contribute to control it and prevent its spread. An online survey was performed to better understand the perception and knowledge of Portuguese and Spanish citizens, regarding pampas grass. The influence of education and occupation, along with age, gender and country of residence, on the knowledge and perceptions of respondents was analysed. The questionnaire was answered by 486 and 839 citizens in Portugal (PT) and Spain (ES), respectively. Most respondents were between 41 and 64 years old, mostly women in Portugal and equally women and men in Spain, with higher education and working mostly in the services sector. The majority of respondents in both countries recognized the plant, knew it is invasive and were able to name it, alerting to a possible bias of the target audience toward citizens already aware of the invasiveness of the pampas grass. Fewer respondents were aware of the legislation that limits its use, and most were unable to identify particular characteristics of the species. The results showed that respondents' occupation in PT and education in ES influenced their knowledge and perception about pampas grass. This study confirms that education and raising awareness regarding invasive species is of utmost importance, as respondents identified academic training and projects with a strong focus on public awareness as the main sources of knowledge regarding pampas grass. Better informed citizens can be part of the solution rather than part of the problem, especially regarding invasive species with such ornamental interest as pampas grass. Supplementary Information: The online version contains supplementary material available at 10.1007/s10530-023-03025-3.

Knowledge and perceptions of invasive plant biocontrol in Europe versus the rest of the world.

Biological control (BC) of invasive alien plants (IAP) can be an effective environmental management approach. It has only very recently been adopted in Europe and is underutilized compared to other continents where this method has been successfully implemented for over a century. This is in sharp contrast to the BC of invertebrate pests, which has been taken up widely within Europe. It has been suggested that this is related to the risk-adverse attitude of Europeans towards weed BC. Scientific and public perception have a major influence on environmental policy actions. Public perception and knowledge regarding BC is an understudied subject despite its relevance for the application of this management alternative. We aimed to assess the knowledge and perception of BC of IAP among European professionals compared with their peers from other continents. To this end we conducted an online survey including multiple choice and open questions among over 700 people professionally engaged with managing the natural environment, of which approximately half were from Europe (EU) and the others from outside (non-EU). We assessed relationships between the geographical location of the respondents and their knowledge, and perceptions of BC of weeds versus BC of invertebrate pests. We found that respondents' location influenced both perceptions and knowledge of BC for weeds. Compared to non-EU respondents, EU professionals showed less appreciation for BC (e.g., regarding safety, sustainability, and cost-effectiveness), and perceived it as a riskier method, particularly in the case of practitioners and researchers. More profoundly insect pest BC tended to be considered less safe than weed BC for non-EU respondents. Confidence in weed BC as a method, as well as in the validity of the associated pre-release risk assessments, strongly increased with the level of expertise in weed BC. While a much higher proportion of non-EU respondents were correctly aware of the presence/absence of BC in their own countries and identified successful examples of BC accurately, both groups of respondents were similarly aware of unsuccessful BC examples, including BC agents against animals, stressing the bias of EU respondents towards examples of BC failure. The appreciation of weed BC in Europe could be elevated by a combination of increasing knowledge of the technique and pre-release risk assessment and promoting successful examples of weed BC, which may bring major benefits for the management of IAP across the region.

Establishment, spread and early impacts of the first biocontrol agent against an invasive plant in continental Europe.

Classical biocontrol is key for the successful management of invasive alien plants; yet, it is still relatively new in Europe. Although post-release monitoring is essential to evaluate the effectiveness of a biocontrol agent, it is often neglected. This study reports the detailed post-release monitoring of the first biocontrol agent intentionally introduced against an invasive plant in continental Europe. The Australian bud-galling wasp Trichilogaster acaciaelongifoliae (Frogatt) is used to control the invasive Acacia longifolia (Andr.) Willd., with a long history of success in South Africa. This biocontrol agent was first released in Europe in 2015 at several sites along the Portuguese coast. We monitored the establishment, spread and early impacts of T. acaciaelongifoliae on target-plants in Portugal, across 61 sites, from 2015 to 2020. Initial release of adults emerging from galls imported from South Africa and the subsequent releases from galls established in Portugal (2018 onwards) was compared, assessing the implications of the hemisphere shift. The impacts on the reproductive output and vegetative growth of A. longifolia were evaluated in more detail at three sites. From 2015 to 2019, 3567 T. acaciaelongifoliae were released at 61 sites, with establishment confirmed at 36 sites by 2020. The transfer of the wasp from the southern hemisphere limited its initial establishment, but increased rates of establishment followed with synchronization of its life cycle with northern hemisphere conditions. Therefore, after an initial moderate establishment, T. acaciaelongifoliae adapted to the northern hemisphere conditions and experienced an exponential growth (from 66 galls by 2016, to 24000 galls by 2018). Galled A. longifolia branches produced significantly fewer pods (-84.1%), seeds (-95.2%) and secondary branches (-33.3%) and had fewer phyllodes but increased growth of the main branch compared to ungalled branches. Trichilogaster acaciaelongifoliae successfully established in the northern hemisphere, despite the initial phenological mismatch and adverse weather conditions. To achieve this, it had to establish and synchronize its life cycle with the phenology of its host-plant, after which it developed exponentially and began to show significant impacts on the reproductive output of A. longifolia.

Global Actions for Managing Cactus Invasions.

The family Cactaceae Juss. contains some of the most widespread and damaging invasive alien plant species in the world, with Australia (39 species), South Africa (35) and Spain (24) being the main hotspots of invasion. The Global Cactus Working Group (IOBC GCWG) was launched in 2015 to improve international collaboration and identify key actions that can be taken to limit the impacts caused by cactus invasions worldwide. Based on the results of an on-line survey, information collated from a review of the scientific and grey literature, expertise of the authors, and because invasiveness appears to vary predictably across the family, we (the IOBC GCWG): (1) recommend that invasive and potentially invasive cacti are regulated, and to assist with this propose five risk categories; (2) recommend that cactus invasions are treated physically or chemically before they become widespread; (3) advocate the use of biological control to manage widespread invasive species; and (4) encourage the development of public awareness and engagement initiatives to integrate all available knowledge and perspectives in the development and implementation of management actions, and address conflicts of interest, especially with the agricultural and ornamental sectors. Implementing these recommendations will require global co-operation. The IOBC GCWG aims to assist with this process though the dissemination of information and experience.

Global effects of non-native tree species on multiple ecosystem services.

Non-native tree (NNT) species have been transported worldwide to create or enhance services that are fundamental for human well-being, such as timber provision, erosion control or ornamental value; yet NNTs can also produce undesired effects, such as fire proneness or pollen allergenicity. Despite the variety of effects that NNTs have on multiple ecosystem services, a global quantitative assessment of their costs and benefits is still lacking. Such information is critical for decision-making, management and sustainable exploitation of NNTs. We present here a global assessment of NNT effects on the three main categories of ecosystem services, including regulating (RES), provisioning (PES) and cultural services (CES), and on an ecosystem disservice (EDS), i.e. pollen allergenicity. By searching the scientific literature, country forestry reports, and social media, we compiled a global data set of 1683 case studies from over 125 NNT species, covering 44 countries, all continents but Antarctica, and seven biomes. Using different meta-analysis techniques, we found that, while NNTs increase most RES (e.g. climate regulation, soil erosion control, fertility and formation), they decrease PES (e.g. NNTs contribute less than native trees to global timber provision). Also, they have different effects on CES (e.g. increase aesthetic values but decrease scientific interest), and no effect on the EDS considered. NNT effects on each ecosystem (dis)service showed a strong context dependency, varying across NNT types, biomes and socio-economic conditions. For instance, some RES are increased more by NNTs able to fix atmospheric nitrogen, and when the ecosystem is located in low-latitude biomes; some CES are increased more by NNTs in less-wealthy countries or in countries with higher gross domestic products. The effects of NNTs on several ecosystem (dis)services exhibited some synergies (e.g. among soil fertility, soil formation and climate regulation or between aesthetic values and pollen allergenicity), but also trade-offs (e.g. between fire regulation and soil erosion control). Our analyses provide a quantitative understanding of the complex synergies, trade-offs and context dependencies involved for the effects of NNTs that is essential for attaining a sustained provision of ecosystem services.

Stakeholder engagement in the study and management of invasive alien species.

Invasive alien species are a major driver of global environmental change and a range of management interventions are needed to manage their effects on biodiversity, ecosystem services, human well-being and local livelihoods. Stakeholder engagement is widely advocated to integrate diverse knowledge and perspectives in the management of invasive species and to deal with potential conflicts of interest. We reviewed the literature in the ISI Web of Science on stakeholder engagement (the process of involving stakeholders (actors) in decision making, management actions and knowledge creation) in invasion science to assess and understand what has been done (looking at approaches and methodologies used, stakeholders involved, and outcomes from engagement) and to make recommendations for future work. Research on stakeholder engagement in invasion science has increased over the last decade, helping to improve scientific knowledge and contributing towards policy formulation and co-implementation of management. However, many challenges remain and engagement could be made more effective. For example, most studies engage only one stakeholder group passively using questionnaires, primarily for assessing local knowledge and perceptions. Although useful for management and policy planning, these stakeholders are not active participants and there is no two-way flow of knowledge. To make stakeholder involvement more useful, we encourage more integrative and collaborative engagement to (1) improve co-design, co-creation and co-implementation of research and management actions; (2) promote social learning and provide feedback to stakeholders; (3) enhance collaboration and partnerships beyond the natural sciences and academia (interdisciplinary and transdisciplinary collaboration); and (4) discuss some practical and policy suggestions for improving stakeholder engagement in invasion science research and management. This will help facilitate different stakeholders to work better together, allowing problems associated with biological invasions to be tackled more holistically and successfully.

Mapping the Flowering of an Invasive Plant Using Unmanned Aerial Vehicles: Is There Potential for Biocontrol Monitoring?

Invasion by alien species is a worldwide phenomenon with negative consequences at both natural and production areas. Acacia longifolia is an invasive shrub/small tree well known for its negative ecological impacts in several places around the world. The recent introduction of a biocontrol agent (Trichilogaster acaciaelongifoliae), an Australian bud-galling wasp which decreases flowering of A. longifolia, in Portugal, demands the development of a cost-efficient method to monitor its establishment. We tested how unmanned aerial vehicles (UAV) can be used to map A. longifolia flowering. Our core assumption is as the population of the biocontrol agent increases, its impacts on the reduction of A. longifolia flowering will be increasingly visible. Additionally, we tested if there is a simple linear correlation between the number of flowers of A. longifolia counted in field and the area covered by flowers in the UAV imagery. UAV imagery was acquired over seven coastal areas including frontal dunes, interior sand dunes and pine forests considering two phenological stages: peak and off-peak flowering season. The number of flowers of A. longifolia was counted, in a minimum of 60 1 m2 quadrats per study area. For each study area, flower presence/absence maps were obtained using supervised Random Forest. The correlation between the number of flowers and the area covered by flowering plants could then be tested. The flowering of A. longifolia was mapped using UAV mounted with RGB and CIR Cannon IXUS/ELPH cameras (Overall Accuracy > 0.96; Cohen's Kappa > 0.85) varying according to habitat type and flowering season. The correlation between the number of flowers counted and the area covered by flowering was weak (r2 between 0.0134 and 0.156). This is probably explained, at least partially, by the high variability of A. longifolia in what regards flowering morphology and distribution. The very high accuracy of our approach to map A. longifolia flowering proved to be cost efficient and replicable, showing great potential for detecting the future decrease in flowering promoted by the biocontrol agent. The attempt to provide a low-cost method to estimate A. longifolia flower productivity using UAV failed, but it provided valuable insights on the future steps.

Four-trophic level food webs reveal the cascading impacts of an invasive plant targeted for biocontrol.

Biological invasions are a major threat to biodiversity and as such understanding their impacts is a research priority. Ecological networks provide a valuable tool to explore such impacts at the community level, and can be particularly insightful for planning and monitoring biocontrol programmes, including the potential for their seldom evaluated indirect non-target effects. Acacia longifolia is among the worst invasive species in Portugal, and has been recently targeted for biocontrol by a highly specific gall-wasp. Here we use an ambitious replicated network approach to: (1) identify the mechanisms by which direct and indirect impacts of A. longifolia can cascade from plants to higher trophic levels, including gallers, their parasitoids and inquilines; (2) reveal the structure of the interaction networks between plants, gallers, parasitoids and inquilines before the biocontrol; and (3) explore the potential for indirect interactions among gallers, including those established with the biocontrol agent, via apparent competition. Over a 15-month period, we collected 31,737 galls from native plants and identified all emerging insects, quantifying the interactions between 219 plant-, 49 galler-, 65 parasitoid- and 87 inquiline-species-one of the largest ecological networks to date. No galls were found on any of the 16 alien plant species. Invasion by A. longifolia caused an alarming simplification of plant communities, with cascading effects to higher trophic levels, namely: a decline of overall gall biomass, and on the richness, abundance and biomass of galler insects, their parasitoids, and inquilines. Correspondingly, we detected a significant decline in the richness of interactions between plants and galls. The invasion tended to increase overall interaction evenness by promoting the local extinction of the native plants that sustained more gall species. However, highly idiosyncratic responses hindered the detection of further consistent changes in network topology. Predictions of indirect effects of the biocontrol on native gallers via apparent competition ranged from negligible to highly significant. Such scenarios are incredibly hard to predict, but even if there are risks of indirect effects it is critical to weigh them carefully against the consequences of inaction and invasive species spread.

Seed ecology of an invasive alien species, Acacia longifolia (Fabaceae), in Portuguese dune ecosystems.

PREMISE OF THE STUDY: Worldwide, invasive plants threaten biodiversity, by disrupting habitats and ecosystem processes, and cause major economic losses. Invasiveness in plants is frequently associated with prolific production of seeds that accumulate in the soil. Knowledge of the extent and persistence of invasive seed banks helps explain invasion processes and enables management planning. A study of Acacia longifolia, an invasive species in Portuguese dune ecosystems, provides an informative example. • METHODS: Seed rain and dispersal (seed traps), the persistence of seeds in the soil (burial), and the extent of seed banks were measured and analyzed. • KEY RESULTS: Seed rain is concentrated under the canopy with about 12000 seeds · m(-2) falling annually. The number of seeds in the soil declined with time, with only 30% surviving after 75 mo. Losses were lowest at greater depths. Seed germinability was low (<12%), but viability was high (>85%) for surviving seeds. The seed bank under the canopy was approximately 1500 and 500 seeds · m(-2) in long- and recently invaded stands, respectively. Some seeds were found up to 7 m from the edge of stands, indicating that outside agencies facilitate dispersal. • CONCLUSIONS: Acacia longifolia produces large numbers of seeds, some of which are lost through germination, decay, and granivory. The remainder form vast and persistent seed banks that serve as a source of replenishment and make it difficult to control the invader once it is established. Control costs escalate as the duration of an invasion increases, highlighting the urgency of initiating and persevering with control efforts.