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Cities often exhibit higher temperatures, drier soils and greater habitat fragmentation than rural areas, and may thus represent constraining growing environments for plants. This variety of environmental conditions along urban-to-rural gradients might lead to plasticity in plant traits. Urban conditions could affect plant traits such as germination or flower number - key variables for organismal fitness. These proxies of fitness could then potentially experience strong selection in urban environments. Trait variations among individuals are not only due to genotype or the environmental conditions: they can also result from the conditions in which the mother individual developed, i.e. environmental maternal effects. Understanding the impact of city environments on phenotypes might be especially important for alien plant species, as these are often showing exceptionally high density and diversity in cities. However, studies of the sources of alien plant trait variations in urban environments are rare. We conducted a simulated reciprocal common garden experiment using seeds of populations of M. discoidea along urbanization gradients in Belgium. These seeds were sown in growth chambers to study how germination, growth, and flowering traits of the alien species Matricaria discoidea vary in response to temperature (rural or urban) and soil (rural or urban) treatments and the urbanity (percentage of impervious surfaces) of its source population. We found predominant effects of seed mass and germination delay which materialized important environmental maternal effects. We observed a higher germination success and delay for heavier seeds, and a greater number of capitula and dry biomass for plants that germinated earlier. Climate and soil treatments led to plasticity in the majority of the measured traits, with a faster germination and heavier plants in the urban temperature treatment but lighter plants in the urban soil treatment. Our results therefore support the existence of predominant environmental maternal effects and phenotypic plasticity in response to temperature and soil treatments, but no visible evidence of local adaptation.

Urban environments often host a greater abundance and diversity of alien plant species than rural areas. This is frequently linked to higher disturbance and propagule pressure, but could also be related to the additional establishment of species from warmer native ranges in cities, facilitated by the latter's higher air temperatures and drier soils. A hitherto unresolved question is how stressful the urban environments become during climate extremes such as heatwaves and droughts. Do such episodes still favor alien plant species, or set them back? We used in situ measured phenotypic leaf and development trait responses of the six most widespread alien Asteraceae species from various native climates along Belgian urban‐to‐rural gradients, measured during two unusually warm and dry summers. Urbanization was characterized by three factors: the percentage of artificially sealed surfaces (urbanity, measured at three spatial scales from in situ to satellite‐based), the vegetation cover and the sky view factor (SVF, fraction of the hemisphere not blocked by buildings or vegetation). Across species, either from colder or warmer native climates, we found a predominant protective effect of shielded environments that block solar radiation (low SVF) along the entire urban‐to‐rural gradient. Such environments induced lower leaf anthocyanins and flavonols indices, indicating heat stress mitigation. Shielded environments also increased specific leaf area (SLA), a typical shade response. We found that vegetated areas had a secondary importance, increasing the chlorophyll content and decreasing the flavonols index, but these effects were not consistent across species. Finally, urbanity at the organism spatial scale decreased plant height, while broader‐scale urbanity had no significant influence. Our results suggest that sealed surfaces constrain alien Asteraceae during unusually warm and dry summers, while shielded environments protect them, possibly canceling out the lack of light. These findings shed new light on alien plant species success along urban‐to‐rural gradients in a changing climate., Sealed surfaces constrain alien Asteraceae during unusually warm and dry summers, while shielded environments protect them, possibly cancelling out the lack of light. These findings shed new light on alien plant species success along urban‐to‐rural gradients in a changing climate.

International audience; Ambrosia trifida L. (giant ragweed, Asteraceae) is native to the North American continent and was introduced into Europe and Asia at the end of the 19th century. In its native range, this tall annual species is common in riparian and ruderal habitats and is also a major weed in annual cropping systems. For nearly a century, A. trifida has also been of great concern in the U.S. for its highly allergenic pollen, necessitating targeted control measures to reduce its impact on human populations. Based on the distribution of A. trifida in North America and in its introduced range, riparian systems in the rest of the world may be particularly at risk to invasion, with potential negative consequences for their biodiversity. Currently, A. trifida has invaded Asia more widely than Europe, likely due to the more favourable local conditions in Asia. Throughout its introduced range, A. trifida is host to a limited number of invertebrates and pathogens and only a few biological agents are available for its control. The main impacts of A. trifida at a global level are on crop yield and human health, resulting in significant socio-economic impacts. The success of A. trifida invasion in areas in which it has been introduced is still unclear, but climate change may increase climate suitability, increasing the potential for A. trifida to spread. While effective management in cultivated fields seems potentially possible, the development and control of A. trifida in natural riparian habitats is of great concern due to the difficulty of management in these areas.

Description of the subject. Common Ragweed (Ambrosia artemisiifolia L.) is a problematic invasive plant which population has recently spread/increased throughout Belgium. Previous studies in European countries have pointed out wild bird and poultry feed trade as a vector of introduction. In 2011, a maximum limit of contamination was imposed by the European commission. Objectives. The goal is to quantify the level of bird seed contamination sold in Southern Belgium. Method. In 2021, we analyzed 42 bags of bird feed, purchased in various retailers in Southern Belgium. We distinguished wild bird seed mixes, poultry seed mixes and sunflower seeds. Results. Regardless of the moisture of the samples (not measured), the results of the samples were not near the legal limit. However, 13 out of 42 samples contained common ragweed seeds and 0.75 ± 0.265 seeds (mean ± standard error) per kilo of bird feed were found on average, of which 82.4% were viable. Conclusions. Although the legal limit seems to be respected, the bird feed trade still represents a substantial introduction pathway for ragweed.

International audience; When colonizing new areas, alien plant species success can depend strongly on local environmental conditions. Microclimatic barriers might be the reason why some alien plant species thrive in urban areas, while others prefer rural environments. We tested the hypothesis that the climate in the native range is a good predictor of the urbanity of alien species in the invaded range. The relationship between climate in the native range and the percentage of artificially sealed surfaces (urbanity) at the occurrences of 24 emerging alien plant species, in European areas with a temperate climate (termed oceanic Europe) was evaluated. We found that alien species growing in more urban environments originated from warmer or drier native ranges than found in oceanic Europe. These results have strong conservation implications as climate-warming will likely lift climatic barriers that currently constrain numerous alien plant species to cities, boosting the role of cities as points of entry for invasive plants.

International audience; Local adaptation and the evolution of phenotypic plasticity may facilitate biological invasions. Both processes can enhance germination and seedling recruitment, which are crucial life-history traits for plants. The rate, timing and speed of germination have recently been documented as playing a major role during the invasion process. Black locust (Robinia pseudoacacia L.) is a North American tree, which has spread widely throughout Europe. A recent study demonstrated that a few populations are the source of European black locust. Thus, invasive populations can be compared to native ones in order to identify genetic-based phenotypic differentiation and the role of phenotypic plasticity can thereby be assessed. A quantitative genetics experiment was performed to evaluate 13 juvenile traits of both native and invasive black locust populations (3000 seeds, 20 populations) subjected to three different thermal treatments (18 degrees C, 22 degrees C and 31 degrees C). The results revealed European populations to have a higher germination rate than the native American populations (88% versus 60%), and even when genetic distance between populations was considered. Moreover, this trait showed lower plasticity to temperature in the invasive range than in the native one. Conversely, other studied traits showed high plasticity to temperature, but they responded in a similar way to temperature increase: the warmer the temperature, the higher the growth rate or germination traits values. The demonstrated genetic differentiation between native and invasive populations testifies to a shift between ranges for the maximum germination percentage. This pattern could be due to human-mediated introduction of black locust.

Habitats being restored in Belgian quarries are easily invaded by non-native plant species, which can hamper the germination and development of vegetation deemed to be of high conservation value. Substrates of terraces created when mining limestone quarries could be inhospitable to native plants. However, they can provide opportunities for establishing specific vegetation, such as dry calcareous grasslands. Applying suitable mining spoils could be a cost-effective way to provide growing substrate when restoring limestone terraces. We assessed the efficacy of using mining spoils, collected on-site, as a potential growing substrate (bedding material). We tested gravely limestone (product of on-site mining activities), limestone dust (by-product), and no addition (bare limestone bedrock) to determine which was best for favoring the growth of native, dry calcareous grassland species and discourage the growth of two non-native invasive species that commonly invade altered mining sites: Buddleja davidii Franch and Senecio inaequidens DC. In a field experiment (in two quarries), we studied short-term (2 y) growth response of native and invasive species after sowing three seed mixtures of native grassland species, varying in functional diversity (and one no-sowing control treatment), all treatments subjected to competitive pressure exerted by invasive species. Percent cover of native and invasive species, species abundance and reproductive characteristics of the invasive species were monitored during 2-y. Native grasslands coverage was low on all substrate types, demonstrating how slowly calcareous grasslands species establish in such harsh substrate conditions. However, type of substrate did show a significant relationship with plant abundance, with limestone dust being the most beneficial for native species establishment (coverage). Although limestone dust appeared to be the best option for restoring grassland species to limestone quarries (based on its low cost, wide availability, and potential to support native species), it was also likely to support the two invasive species. Functional diversity of the seed mixture had no consistent effect. Our study shows the importance of identifying the most appropriate substrate to both establish calcareous grasslands and resist invasive species. This approach provides insights into developing strategies to conserve biodiversity in industrial and agricultural landscapes with limestone quarries.

In agricultural fields, wildflower strips can be sown to enhance conservation biological control of insect pests. However, issues remain regarding the composition of flower mixtures to effectively attract and support large communities of natural enemies. Trait-based approaches are promising for this purpose. In the present study, conducted in an agricultural field of Belgium in 2014 and 2015, 15 flower mixtures were considered to explore the relation between the abundance of trapped generalist predators (i.e. lacewings [Neuroptera: Chrysopidae], ladybeetles [Coleoptera: Coccinellidae] and hoverflies [Diptera: Syrphidae]) and the community-weighted means of seven flower traits. Through a redundancy analysis, it was found that the presence/absence of flower ultra-violet pattern and the morphology of the corolla (that determines the accessibility of floral resources) were the traits that significantly affected the abundance of the generalist predators in the flower mixtures. The ladybeetles Harmonia axyridis and Propylea quatuordecimpunctata as well as the lacewings Chrysoperla carnea were more abundant in mixtures with a high cover of flowers showing an ultra-violet pattern, while the opposite was observed for the ladybeetle Coccinella septempunctata. As for hoverflies, Episyrphus balteatus and Eupeodes corollae were more abundant in mixtures with a high cover of flowers with open nectar. These results bring new knowledge regarding how a range of natural enemy species reacts to flower cues in diversified plant communities and should help in elaborating flower mixtures that enhance conservation biological control.

Intensification of agriculture has been one of the major drivers for biodiversity loss in recent decades. Pollinators, which serve an important role in pollinating crops as well as wild plants, have shown a decline in species richness. Flower strips can be used to support pollinators in agro-ecosystems, however the question remains as to how their design can be optimized in order to best benefit pollinators. Increasing plant species diversity has been shown to be beneficial for pollinators, and it is often suggested that functional traits are driving this relationship. Therefore, increasing plant functional diversity could be a tool to support pollinator abundance and diversity. As experimental evidence on this relationship is scarce, we developed a field study with experimental sown flower strips with four functional diversity levels, based on multiple flower traits and with equal plant species richness. We monitored vegetation development, as well as the flower-visiting pollinator community and their interaction networks with flowers. We were able to create a functional diversity gradient while controlling for plant species richness and evenness. However, in contrast to our expectations, pollinator species richness and evenness were not influenced by functional diversity, and increasing functional diversity even resulted in lower flower visitation rates. Network stability metrics showed no effect or negative relationships with functional diversity. We conclude that increasing functional diversity was not the key for supporting pollinators in wildflower strips. Our results also suggest that, for a constant amount of flower resources, increasing plant functional diversity and thus decreasing redundancy of potential pollinator feeding niches, decreases the amount of flower resources present per feeding niche. As pollinator species tended to have less overlap in their feeding niches in flower strips with increased functional diversity, this may lead to a reduction of flower resources available for pollinator species with a more specialized feeding niche.

Reducing the use of insecticides is an important issue for agriculture today. Sowing wildflower strips along field margins or within crops represents a promising tool to support natural enemy populations in agricultural landscapes and, thus, enhance conservation biological control. However, it is important to sow appropriate flower species that attract natural enemies efficiently. The presence of prey and hosts may also guide natural enemies to wildflower strips, potentially preventing them from migrating into adjacent crops. Here, we assessed how seven flower traits, along with the abundance of pollen beetles (Meligethes spp., Coleoptera: Nitidulidae) and true weevils (Ceutorhynchus spp., Coleoptera: Curculionidae), affect the density of parasitoids of these two coleopterans in wildflower strips sown in an oilseed rape field in Gembloux (Belgium). Only flower traits, not host (i.e. pollen beetles and true weevils) abundance, significantly affected the density of parasitoids. Flower colour, ultraviolet reflectance and nectar availability were the main drivers affecting parasitoids. These results demonstrate how parasitoids of oilseed rape pests react to flower cues under field conditions. Similar analyses on the pests and natural enemies of other crops are expected to help to develop perennial flower mixtures able to enhance biological control throughout a rotation system.

Évaluation du risque simplifiée du tomato brown rugose fruit virus pour la France métropolitaine. Avis de l'Anses. Rapport d'expertise collective

Among the semi-natural elements in agricultural landscapes, wildflower strips sown at field margins or within fields are potential habitats for the natural enemies of insect pests. As insects are sensitive to a variety of flower traits, we hypothesized that mixtures with high functional diversity attract and support a higher abundance and species richness of aphid flower visiting predators than mixtures with low functional diversity. During a field experiment, repeated over two years (2014 and 2015) in Gembloux (Belgium), aphid predators (i.e., lacewings, ladybeetles and hoverflies) were pan-trapped in five sown flower mixtures (including a control mixture, with three replicates of each mixture) of low to high functional diversity based on seven traits (i.e., flower colour, ultra-violet reflectance and pattern, start and duration of flowering, height and flower class, primarily based on corolla morphology). In both years, the species of flowering plants in the sown mixtures (i.e., sown and spontaneous flowers) were listed, and the realized functional diversity in each plot calculated. Over the two years, a high functional diversity was not associated with high abundance and richness of aphid predators. Moreover, ladybeetles, which made up the majority of the predators trapped, were more abundant in mixtures with very low or intermediate functional diversity at sowing, especially in 2014. We hypothesize that certain flowers, which were abundant in certain mixtures (and not in those exhibiting the highest functional diversity), attracted predators and were sufficiently abundant to support them. Our results present novel information that could be used for developing flower mixtures that provide effective ecosystem services, such as pest control.

In southeastern D. R. Congo, about 550 metallophytes grow on soils with high copper and cobalt concentrations, 57 of which are endemics to these metalliferous environments. About 70% of those endemics are considered threatened by destruction of habitats through mining activities. To provide guidelines for future restoration programs, the edaphic ecological niches of eight endemic metallophytes (i.e. copper endemics) were studied using a pragmatic sampling method adapted for urgent conservation needs. Niches were modelled using violin plot along Cu, Co and C:N gradients representing the two main independent edaphic gradients among nine edaphic variables (C, N, C:N, K, P, pH, Co, Cu, and Mn). Copper endemics presented distinct edaphic niches along the copper and cobalt gradients, but differentiation was lower along the C:N gradient. In addition, edaphic elements presented covariations among them and metalliferous soils had higher nutrient and element content compared to the non-metalliferous soils of the region dominated by the Miombo woodland. The complexity of the soil composition and the edaphic niches of copper endemics revealed an important challenge in the implementation of the species conservation and the habitat restoration strategies of post-mining sites.

Within a species, the distance travelled by a particular diaspore depends on its morphology. In Poaceae, the presence of terminal sterile florets can lead to diaspore heteromorphism, which may influence dispersal. We tested the hypothesis that the presence of sterile florets favored dispersal in Bromus tectorum L., an invasive grass in the Western US. We used field and controlled experiments to study the dispersal of caryopses with and without sterile florets attached (respectively complex and simple diaspores), as well as pieces of inflorescence that detached from the mother plants. We considered both primary and secondary dispersal, as well as abiotic and biotic dispersal agents. The distance travelled by the diaspores and their attachment to animal fur were related to the presence and number of sterile florets. Abiotic agents moved diaspores over relatively short distances, both in terms of primary and secondary dispersal. A significant proportion of diaspores attached to fur, suggesting a potential for dispersal over long distances. Complex diaspores were better dispersers than simple ones (and pieces of inflorescence), and this pattern was consistent across the study. However, among complex diaspores, the number of sterile florets had little or no influence. Considering primary and secondary dispersal by abiotic and biotic agents provided a general picture of the dispersal ecology of B. tectorum . For all the dispersal steps and dispersal agents we studied, the presence of sterile florets favored dispersal. These results highlight the functional significance of diaspore heteromorphism induced by floret sterility in the dispersal of Poaceae.

International audience; The role of evolution in biological invasion studies is often overlooked. In order to evaluate the evolutionary mechanisms behind invasiveness, it is crucial to identify the source populations of the introduction. Studies in population genetics were carried out on Robinia pseudoacacia L., a North American tree which is now one of the worst invasive tree species in Europe. We realized large‐scale sampling in both the invasive and native ranges: 63 populations were sampled and 818 individuals were genotyped using 113 SNPs. We identified clonal genotypes in each population and analyzed between and within range population structure, and then, we compared genetic diversity between ranges, enlarging the number of SNPs to mitigate the ascertainment bias. First, we demonstrated that European black locust was introduced from just a limited number of populations located in the Appalachian Mountains, which is in agreement with the historical documents briefly reviewed in this study. Within America, population structure reflected the effects of long‐term processes, whereas in Europe it was largely impacted by human activities. Second, we showed that there is a genetic bottleneck between the ranges with a decrease in allelic richness and total number of alleles in Europe. Lastly, we found more clonality within European populations. Black locust became invasive in Europe despite being introduced from a reduced part of its native distribution. Our results suggest that human activity, such as breeding programs in Europe and the seed trade throughout the introduced range, had a major role in promoting invasion; therefore, the introduction of the missing American genetic cluster to Europe should be avoided.

The reintroduction of plant species is a technique increasingly used to restore extirpated populations. Although most often used to improve the conservation status of endangered species, it can also be considered for species extinct in the wild. The process of resurrecting extinct plant species is however still in its infancy, and it entails additional challenges compared to the reintroduction of locally extinct populations. This study proposes a framework to analyse constraints to post-extinction recovery based on the case of Bromus bromoideus, a species endemic to southern Belgium and northern France, extinct in the wild since 1935. The plant still exists in ex situ collections, and seeds stored for decades at 5% moisture content and -20 °C have shown a good viability. We initiated a feasibility study to assess the risks associated to a programme aiming at reviving this long-extinct species. Several constraints were identified. Biological constraints are related to the fuzzy taxonomy of the species, the unknown origin of the seeds and undocumented ex situ cultivation, and the likely low genetic diversity of the material available for reintroduction. Ecological constraints are linked to the habitat of the species. B. bromoideus has no known natural habitat and is only found in cultivated fields, which are by definition highly anthropized unprotected areas. This study shows the importance of undertaking a preliminary study that addresses all aspects of technical feasibility, scientific justification, biological and societal risks. Based on this exercise and inspired by international standards, we developed a decision tool to assist conservationists to resurrect a plant species in the best possible way.

International audience; Background – The role of evolution in biological invasion studies is often overlooked. In order to evaluate the evolutionary mechanisms behind invasiveness, both quantitative and population genetics studies are underway on Robinia pseudoacacia L., one of the worst invasive tree species in Europe. Methods – A controlled experiment was set up using 2000 seeds from ten populations in Southern France and ten populations in Belgium. Seedlings were cultivated in two climatic chambers set at 18°C and 22°C. Early development life history traits (e.g.seedling phenology) and functional traits (e.g.growth rates) were monitored. Genotyping using SNP markers was used to evaluate the genetic differentiation among the populations and a QST – FST comparison was done in order to test for the role of selection. Results – Populations exhibited a strong plasticity to temperature for all measured traits, the warmer environment being generally more suitable, irrespective of their origin. No significant departure from neutral evolution was evidenced by the QST – FST comparisons, although we found a slightly significant differentiation at the molecular level. Conclusion – Plasticity for the functional and life history traits was evidenced but no genetic interaction suggesting no possible evolution of plasticity at those traits. Moreover, no support for genetic differentiation and local adaptation was found among studied populations within invasive range, raising two main questions: first, what is the role of selection on functional and life-history traits; and second, is the elapsed time since first introduction sufficient to allow evolution and local adaptation?

Seedling performance can determine the survival of a juvenile plant and impact adult plant performance. Understanding the factors that may impact seedling performance is thus critical, especially for annuals, opportunists or invasive plant species. Seedling performance can vary among mothers or populations in response to environmental conditions or under the influence of seed traits. However, very few studies have investigated seed traits variations and their consequences on seedling performance. Specifically, the following questions have been addressed by this work: 1) How the seed traits of the invasive Ambrosia artemisiifolia L. vary among mothers and populations, as well as along the latitude; 2) How do seed traits influence seedling performance; 3) Is the influence on seedlings temperature dependent. With seeds from nine Western Europe ruderal populations, seed traits that can influence seedling development were measured. The seeds were sown into growth chambers with warmer or colder temperature treatments. During seedling growth, performance-related traits were measured. A high variability in seed traits was highlighted. Variation was determined by the mother identity and population, but not latitude. Together, the temperature, population and the identity of the mother had an effect on seedling performance. Seed traits had a relative impact on seedling performance, but this did not appear to be temperature dependent. Seedling performance exhibited a strong plastic response to the temperature, was shaped by the identity of the mother and the population, and was influenced by a number of seed traits.

Background and aims – Calcareous grasslands are local biodiversity hotspots in temperate regions that suffered intensive fragmentation. Ecological restoration projects took place all over Europe. Their success has traditionally been assessed using a plant community approach. However, population ecology can also be useful to assess restoration success and to understand underlying mechanisms. Methods – We took advantage of three calcareous grassland sites in Southern Belgium, where reference parcels coexist with parcels restored in the late twentieth century and with more recently restored parcels. We evaluated the colonization stage of three specialist species ( Sanguisorba minor, Potentilla neumanniana and Hippocrepis comosa ) using occurrence data. We also measured the reproductive traits of 120 individuals per species and compared components of fitness between recent restorations, old restorations and reference habitats. Key results – We found that the occurrence of H. comosa was similar in the different restoration classes, whereas both P. neumanniana and S. minor occurrences decreased from reference grasslands to recent restorations. In contrast, these two latter species exhibited a much higher reproductive output in recent restorations, thanks to an increased production of flowers and seeds. Conclusions – Our results suggest that, during colonization of recently restored calcareous grasslands, favourable environmental conditions, low competition and sufficient genetic mixing may lead to an increased fitness of individuals and a faster population growth than in the reference habitat. These results demonstrate how population processes can increase ecological resilience and highlight the interest of a population-based approach to assess the success of ecological restoration.

Analyse de risque phytosanitaire portant sur la berce du Caucase

Reducing pesticide use is one the major issues of today's agriculture. Among other possibilities, attracting and conserving pest natural enemies in agricultural landscapes by providing them habitats is promising. Wildflower strips (WFS) sown at field margins are one of these potential habitats. They are known to attract and conserve a large diversity of insects, as they provide them food resources such as pollen and nectar, as well as shelter and overwintering sites. However, the risk of attracting insect pests at field margins may represent an obstacle to their adoption by farmers. Conversely, it would be interesting if such WFS could play the role of pest trap crops. In an experimental field sown with WFS intercropped with oilseed rape (OSR) (Brassica napus L.), its coleopteran pests were trapped in both WFS and OSR using yellow pan traps between April and June 2014. More than 130 000 Meligethes spp., Ceutorhynchus spp. and Psylliodes chrysocephalla (L.) adults were trapped. Meligethes spp., Ceutorhynchus spp. were significantly more abundant in the OSR compared with WFS when adults emerged and populations reached their abundance peak. Before and between these periods, the few adults trapped were significantly more abundant in the WFS compared with the OSR. Concerning P. chrysocephala, too few individuals were caught for analysis. Results showed that OSR was more attractive than WFS when coleopteran pests were abundant. In this study, WFS sown for insect conservation may neither favour insect pest conservation at field margin, nor be considered as trap crops.

To ensure the rescue, temporary conservation and further restoration of plant populations and communities threatened by exploitation, translocation appears to be an appropriate method in the context of mining. Little is known, however, on its effect on mutualistic interactions, such as pollination, and on the resulting plant population dynamics. Whole-rock translocations were performed as a conservation strategy for the endemic metallophyte flora of Katanga, Democratic Republic of the Congo. The aim of this study was to quantify the flower visitation, sexual reproduction and ramet demographic structure in such a translocated population, and to compare the data with those from natural populations of Aeollanthus saxatilis, one of the threatened species of the chasmophytic community. The study also documented the plant’s flower visitor guild. The ramet density, demographic structure, pollination success and seed abortion rate were assessed in 10 quadrats per population, in the translocated population and in two subsisting natural populations. The flower visitation rate was quantified during three observation periods (20 min each) in six quadrats per population. Small differences were observed in the visitor guild between the translocated and natural populations, but the flower visitation rate was equivalent. No clear difference in the reproductive performance or ramet demographic structure of the populations was found. The flower visitor guild was mainly composed of generalist pollinators, which probably helped in establishing a functional visitor guild at the receptor site. Rock translocation therefore appears to be an encouraging approach, allowing the conservation of functional mutualistic interactions and the maintenance of a population structure comparable to that of natural chasmophytic plant populations.

International audience; Ecological niche modelling helps us to understand the spatial assembly of species in heterogeneous environments. Three patterns have been widely reported in the research literature regarding the relationship between realised niches and macronutrient concentration gradients: (1) species' optima are unevenly distributed, with a higher frequency in mesic conditions; (2) species' response curves are narrower when optima density is higher; and (3) species with optima at the extremes of the gradients have skewed response curves with a longer tail toward mesic conditions. This study aims to test the existence of these patterns on a vegetation model occurring in metalliferous soils comprising copper and cobalt along a toxicity gradient in southeastern D.R. Congo. Realised niches of 80 taxa were modelled using generalised additive models. The niche optima and the niche widths were determined for each taxon. Results highlighted three groups which differ according to the niche optima location along the soil metal concentration gradients. The patterns found along macronutrient concentration gradients were, to some extent, transposable along micronutrient concentration gradients. Our findings on the diversity and assembly of realised niches has consequences for plant conservation strategies.

Voluntary approaches have been recently used in the horticultural sector to deal with the introduction and spread of invasive alien plants. In Belgium, the first Code of conduct has been developed within the frame of the AlterIAS project, a LIFE+ “Information & Communication” project aiming at raising the awareness of horticulture professionals and gardeners on the invasive plants issue. The Belgian Code was prepared in consultation with representatives from the ornamental sector, public authorities and the scientific community. The Code was promoted throughout the country with a specific communication campaign entitled “Plant different”. Thanks to communication efforts, a positive dynamic of involvement was observed over time. Surveys were performed to assess the changes of attitudes and the perception of the Code by the target audience of the project. Positive results were achieved for horticulture professionals. However, the Code will require more time to be widely adopted by the ornamental sector in Belgium. Code de conduite volontaire sur les plantes envahissantes en Belgique: resultats et retour d'experience du projet AlterIAS LIFE+ Les approches volontaires ont ete recemment utilisees dans le secteur horticole pour limiter l'introduction et la dissemination des plantes exotiques envahissantes. En Belgique, le premier Code de conduite a ete mis au point dans le cadre du projet AlterIAS, un projet LIFE+ « Information & Communication » visant a favoriser la prise de conscience des questions liees aux plantes envahissantes chez les professionnels de l'horticulture et chez les jardiniers. Le Code belge a ete prepare en concertation avec des representants du secteur des plantes ornementales, des autorites publiques, ainsi que de la communaute scientifique. Ce Code a ete mis en avant dans l'ensemble du pays avec une campagne de communication specifique « Plantons autrement ». Grâce aux efforts de communication, une dynamique d'implication positive a ete observee au cours du temps. Des etudes ont ete menees pour evaluer les changements d'attitudes et la perception du Code par son public cible. Des resultats positifs ont ete obtenus aupres des professionnels de l'horticulture. Le Code demandera cependant plus de temps pour etre adopte de maniere plus large par le secteur ornemental en Belgique. Дoбpoвoльный Кoдeкc пoвeдeния в oтнoшeнии инвaзивныx чyжepoдныx pacтeний в Бeльгии: peзyльтaты и ypoки, извлeчeнныe из пpoeктa AlterIAS LIFE+ Дoбpoвoльныe пoдxoды нeдaвнo иcпoльзoвaлиcь в ceктope caдoвoдcтвa для paбoты c интpoдyкциeй и pacпpocтpaнeниeм чyжepoдныx инвaзивныx pacтeний. B Бeльгии пepвыe кoдeкcы пoвeдeния были paзpaбoтaны в paмкax пpoeктa AlterIAS LIFE+ «Инфopмaция и Кoммyникaция», нaцeлeннoгo нa пoвышeниe ocвeдoмлeннocти пpoфeccиoнaлoв плoдoвoдcтвa и caдoвoдoв в oтнoшeнии пpoблeмы инвaзивныx pacтeний. Бeльгийcкий Кoдeкc был пoдгoтoвлeн в xoдe кoнcyльтaций c пpeдcтaвитeлями ceктopa дeкopaтивныx pacтeний, opгaнoв гocyдapcтвeннoй влacти и нayчнoгo cooбщecтвa. Блaгoдapя нayчнo-пpocвeтитeльcкoй кaмпaнии пoд нaзвaниeм «Caжaй c oглядкoй», кoдeкc pacпpocтpaнялcя пo вceй cтpaнe, и в тeчeниe дoлгoгo вpeмeни oтмeчaлacь пoлoжитeльнaя динaмикa вoвлeчeннocти. Были пpoвeдeны oпpocы, пoзвoляющиe oцeнить измeнeния пcиxoлoгичecкиx ycтaнoвoк и вocпpиятия Кoдeкca цeлeвoй ayдитopиeй пpoeктa. B oтнoшeнии пpoфeccиoнaлoв плoдoвoдcтвa были дocтигнyты пoлoжитeльныe peзyльтaты. Oднaкo пoтpeбyeтcя бoльшe вpeмeни для шиpoкoгo пpинятия Кoдeкca ceктopoм дeкopaтивныx pacтeний в Бeльгии.

Physical dormancy ofRobinia pseudoacaciaseeds makes it a challenge for scientists and forest managers to obtain a homogeneous germination for larger seed samples. Water imbibition of the seeds can be achieved through manual piercing of the seed coat, but this method remains time consuming and heterogeneous. We tested several ecologically friendly methods to break seed dormancy, including manual pin puncture, water soaking, oven dry-heating (two temperatures) and sanding. Sanding was performed using an automatic grinder to control shaking duration (three durations) and get a homogeneous scraping of the coat. All methods, except dry-heating, resulted in successful dormancy breaking; water soaking was the least efficient method, attaining 57% germination. Sanding proved to be as efficient as puncturing (97%) but long duration sanding (10 or 15 min) could damage cotyledons, which would impede further development of the plant. Short-time sanding (5 min) proved to be the best method to reach high total germination and healthy (undamaged cotyledon) seedlings, and was successfully applied to 500 seeds. The reference puncture method and the automatic sanding were also tested on seeds of nine Fabaceae species and proved to be efficient for some species. Automated sanding can thus be used as a standard to break physical dormancy of black locust or other Fabaceae seeds to allow further comparative studies of plant populations or genotypes.

Quercus rubra has been introduced in Europe since the end of the 17th century. It is widely distributed today across this continent and considered invasive in some countries. Here, we investigated the distribution of genetic diversity of both native and introduced populations with the aim of tracing the origin of introduced populations. A large sampling of 883 individuals from 73 native and 38 European locations were genotyped at 69 SNPs. In the natural range, we found a continuous geographic gradient of variation with a predominant latitudinal component. We explored the existence of ancestral populations by performing Bayesian clustering analysis and found support for two or three ancestral genetic clusters. Approximate Bayesian Computations analyses based on these two or three clusters support recent extensive secondary contacts between them, suggesting that present-day continuous genetic variation resulted from recent admixture. In the introduced range, one main genetic cluster was not recovered in Europe, suggesting that source populations were preferentially located in the northern part of the natural distribution. However, our results cannot refute the introduction of populations from the southern states that did not survive in Europe.; Le Quercus rubra a été introduit en Europe depuis la fin du 17ème siècle. Il est largement distribué sur tout le continent et il y est considéré comme une espèce envahissante dans certains pays. Dans ce travail, les auteurs ont étudié la distribution de la diversité génétique au sein de populations indigènes et introduites en vue de retracer l’origine des populations introduites. Un échantillon composé de 883 individus, provenant de 73 sites indigènes et 38 sites européen, a été génotypé pour 69 marqueurs SNP. Au sein de l’aire naturelle, les auteurs ont observé un gradient géographique continu avec une composante latitudinale prédominante. Les auteurs ont exploré l’existence de populations ancestrales au moyen d’analyses bayésiennes de groupement et ont trouvé des évidences en faveur de deux ou trois groupes génétiques ancestraux. Des estimations bayésiennes approximatives (« Approximate Bayesian Computations ») basées sur deux ou trois groupes supportent l’existence de contacts secondaires récents et étendus entre eux, ce qui suggère que la variation continue observée aujourd’hui découle d’une admixture récente. Au sein de l’aire d’introduction, un des groupes génétiques principaux n’a pas été trouvé en Europe, ce qui suggère que les populations d’origine étaient principalement situées dans la portion septentrionale de l’aire de distribution naturelle. Cependant, les résultats obtenus ne peuvent exclure la possibilité que des populations provenant des états méridionaux aient été introduites en Europe mais qu’elles n’y aient pas survécu.

The RADseq technology allows researchers to efficiently develop thousands of polymorphic loci across multiple individuals with little or no prior information on the genome. However, many questions remain about the biases inherent to this technology. Notably, sequence misalignments arising from paralogy may affect the development of single nucleotide polymorphism (SNP) markers and the estimation of genetic diversity. We evaluated the impact of putative paralog loci on genetic diversity estimation during the development of SNPs from a RADseq dataset for the nonmodel tree species Robinia pseudoacacia L. We sequenced nine genotypes and analyzed the frequency of putative paralogous RAD loci as a function of both the depth of coverage and the mismatch threshold allowed between loci. Putative paralogy was detected in a very variable number of loci, from 1% to more than 20%, with the depth of coverage having a major influence on the result. Putative paralogy artificially increased the observed degree of polymorphism and resulting estimates of diversity. The choice of the depth of coverage also affected diversity estimation and SNP validation: A low threshold decreased the chances of detecting minor alleles while a high threshold increased allelic dropout. SNP validation was better for the low threshold (4×) than for the high threshold (18×) we tested. Using the strategy developed here, we were able to validate more than 80% of the SNPs tested by means of individual genotyping, resulting in a readily usable set of 330 SNPs, suitable for use in population genetics applications.

Particularly well-known among the many impacts of the invasive annual grass downy brome (Bromus tectorum, Poaceae) is its ability to alter fire cycles and increase in abundance after fire. However, little is known about how fire influences B. tectorum dispersal. We quantified fire effects on B. tectorum dispersal using three recently burned areas in the western region of the Colorado Rocky Mountains by marking diaspores (seeds) with fluorescent powder, and then recovering them at night using ultraviolet lights. Diaspores were of two types: with and without sterile florets attached. We also characterized vegetation cover and near-surface wind speed in burned and unburned areas. Diaspores travelled much farther in burned areas than in nearby unburned areas (mean ± standard error at the end of the experiment: 209 ± 16 cm and 38 ± 1 cm, respectively; maximal distance at the end of the experiment: 2,274 cm and 150 cm, respectively), indicating an increase in dispersal distance after fire. Diaspores with sterile florets attached dispersed longer distances than those without sterile florets (mean ± standard error at the end of the experiment: 141 ± 14 cm and 88 ± 7 cm, respectively). Vegetation cover was lower and wind speeds were higher in the burned areas. Our results indicate that at least one of the mechanisms by which the spread of B. tectorum is promoted by fire is through increased seed dispersal distance. Preventing movement of seeds from nearby infestations into burned areas may help avoid the rapid population expansion often observed.

Japanese knotweed Fallopia japonica is an extremely abundant invasive plant in Belgium and surrounding countries. To date, no eradication method is available for land managers facing the invasion of this rhizomatous plant. We tested different chemical herbicides with two application methods (spraying and stem injection), as well as mechanical treatments, on knotweed clones throughout southern Belgium. The tested control methods were selected to be potentially usable by managers, e.g., using legally accepted rates for herbicides. Stem volume, height and density reduction were assessed after one or two years, depending on the control method. Labor estimations were made for each control method. No tested control method completely eradicated the clones. Stem injection with glyphosate-based herbicide (3.6 kg ha(-1) of acid equivalent glyphosate) caused the most damage, i.e., no sprouting shoots were observed the year following the injection. The following year, though, stunted shoots appeared. Among the mechanical control methods, repeated cuts combined with native tree transplanting most appreciably reduced knotweed development. The most efficient methods we tested could curb knotweed invasion, but are not likely to be effective in eradicating the species. As such, they should be included in a more integrated restoration strategy, together with prevention and public awareness campaigns.

La crassule des etangs (Crassula helmsii) est une plante invasive (ou exotique envahissante) qui represente un risque environnemental pour les milieux aquatiques en Belgique et, plus globalement, en Europe. Pour controler cette espece, les acteurs de terrain disposent d’une litterature a priori abondante, ainsi que de plusieurs bases de donnees relatives a sa distribution spatiale. Neanmoins, les gestionnaires peuvent vite se sentir desarmes, d’une part par le manque de clarte sur les moyens a mettre en œuvre afin d’endiguer la propagation de l’espece et, d’autre part, par le manque d’exhaustivite des bases de donnees. S’ajoute a cela une insuffisance de litterature sur les vecteurs de dissemination a travers les paysages.

The spatio-temporal dynamics of wet heathlands from two landscapes in high Ardenne (Belgium), as well as the consequences of such dynamics on plant communities were investigated. Past and present destruction and origin of habitat patches have resulted in a complex network of different aged habitat patches. Current specialist and generalist species richness were assessed in 59 patches and analyzed with respect to present and past patch spatial metrics (controlled for habitat quality). Current patch area affected specialist species richness and current patch connectivity influenced both specialist and generalist species richness. Thirteen of the 59 patches were historical patches, i.e. patches that have remained since the 1770s. In these historical patches, including past landscape structure in the analysis explained more of the variability in current species richness than the current landscape structure alone, suggesting the existence of an extinction debt.

In introduced organisms, dispersal propensity is expected to increase during range expansion. This prediction is based on the assumption that phenotypic plasticity is low compared to genetic diversity, and an increase in dispersal can be counteracted by the Allee effect. Empirical evidence in support of these hypotheses is however lacking. The present study tested for evidence of differentiation in dispersal-related traits and the Allee effect in the wind-dispersed invasive Senecio inaequidens (Asteraceae). We collected capitula from individuals in ten field populations, along an invasion route including the original introduction site in southern France. In addition, we conducted a common garden experiment from field-collected seeds and obtained capitula from individuals representing the same ten field populations. We analysed phenotypic variation in dispersal traits between field and common garden environments as a function of the distance between populations and the introduction site. Our results revealed low levels of phenotypic differentiation among populations. However, significant clinal variation in dispersal traits was demonstrated in common garden plants representing the invasion route. In field populations, similar trends in dispersal-related traits and evidence of an Allee effect were not detected. In part, our results supported expectations of increased dispersal capacity with range expansion, and emphasized the contribution of phenotypic plasticity under natural conditions.

In recent decades, a growing number of studies have addressed connections between ecological and evolutionary concepts in biologic invasions. These connections may be crucial for understanding the processes underlying invaders’ success. However, the extent to which scientists have worked on the integration of the ecology and evolution of invasive plants is poorly documented, as few attempts have been made to evaluate these efforts in invasion biology research. Such analysis can facilitate recognize well-documented relationships and identify gaps in our knowledge. In this study, we used a network-based method for visualizing the connections between major aspects of ecology and evolution in the primary research literature. Using the family Poaceae as an example, we show that ecological concepts were more studied and better interconnected than were evolutionary concepts. Several possible connections were not documented at all, representing knowledge gaps between ecology and evolution of invaders. Among knowledge gaps, the concepts of plasticity, gene flow, epigenetics and human influence were particularly under-connected. We discuss five possible research avenues to better understand the relationships between ecology and evolution in the success of Poaceae, and of alien plants in general.

An individual distance-independent girth increment model for pure stands of Douglas-fir (Pseudotsuga menziesii (MIRB.) FRANCO), comprising two equations, is presented. The data used to fit the model were collected from 1007 trees in 42 plots in stalled in regularly stocked and even-aged stands l ocated in Wallonia (southern Belgium). Both equations predict girth increment from individual girth, dominant he ight, basal area per hectare, stand mean girth and variab les linked to site fertility. These last variables are the site index H50 in the first equation, and a combination of mean annual rainfall and altitude in the second. The coefficient of determination ranges from 0.434 to 0 .481 and the root mean square error ranges from 0.7 857 to 0.8194 cm year -1 . Estimated increments of 224 Douglas-fir trees in 12 different and independent stands were used to validate the model, which is expected to pr ovide reliable predictions for most of the pure Dou glas-fir stands located in the study area.

International audience; The RADseq technology allows researchers to efficiently develop thousands of polymorphic loci across multiple individuals with little or no prior information on the genome. However, many questions remain about the biases inherent to this technology. Notably, sequence misalignments arising from paralogy may affect the development of single nucleotide polymorphism (SNP) markers and the estimation of genetic diversity. We evaluated the impact of putative paralog loci on genetic diversity estimation during the development of SNPs from a RADseq dataset for the nonmodel tree species Robinia pseudoacacia L. We sequenced nine genotypes and analyzed the frequency of putative paralogous RAD loci as a function of both the depth of coverage and the mismatch threshold allowed between loci. Putative paralogy was detected in a very variable number of loci, from 1% to more than 20%, with the depth of coverage having a major influence on the result. Putative paralogy artificially increased the observed degree of polymorphism and resulting estimates of diversity. The choice of the depth of coverage also affected diversity estimation and SNP validation: A low threshold decreased the chances of detecting minor alleles while a high threshold increased allelic dropout. SNP validation was better for the low threshold (4×) than for the high threshold (18×) we tested. Using the strategy developed here, we were able to validate more than 80% of the SNPs tested by means of individual genotyping, resulting in a readily usable set of 330 SNPs, suitable for use in population genetics applications.

The occurrence of an invasive plant across a continent is generally not homogeneous; typically, some areas are highly invaded whereas others show moderate or low invasion levels. This situation might be a snapshot of an ongoing spread, but it could also remain stable under the pressure of factors that constrain the invasion. Among those factors, plant performance variation among invasion levels can explain an invasion slowdown. However, few studies have investigated the large-scale variation of invasive plant performance in the field. Ambrosia artemisiifolia L. in Western Europe represents a good opportunity to address this issue, with areas of high, moderate and low invasion levels being documented across a ca. 1000 km transect. In this study, we compared in situ plant performance-related traits in 12 populations from areas of contrasting invasion levels. We also tested whether performance-related traits were influenced by the intra-and inter-specific competition, by the local climatic conditions or by latitude (a proxy for growing season length). Overall, we did not find differences in performance-related traits across invasion levels, and intra-and inter-specific competition had low effects on plant performance. This study highlights the fact that A. artemisiifolia individuals express similar performance across invasion levels, even beyond what can be considered the present invasion front. Further research has to expand this study northwards, and assess other factors that could constrain the invasion in order to highlight if the species invasion northward is constrained or if it has the potential to invade new areas.

Pollination systems based on indirect rewards, such as heat and shelter, have seldom been studied. Plant–pollinator interactions were characterized in Iris cedretii Dinsmore ex Chaudhary and Iris sofarana subsp. kasruwana Dinsmore ex Chaudhary, rare endemic Lebanese Oncocyclus irises exhibiting potential adaptation to shelter pollination. Despite a diversity of floral visitors (47 species), only two groups of Anthophoridae male bees ( Xylocopa spp. and Eucera spp.) could be considered as efficient pollinators on the basis of frequency of visits, visiting behaviour, and pollen load. Lebanese Oncocyclus irises showed a bimodal pollination system with (1) diurnal visits at low rates but with potentially large pollen transfers by Xylocopa bees, exhibiting a foraging-like behaviour, principally during warm periods of the day and (2) sheltering, especially Eucera male bees, during night and day when the weather is changeable. Refuge occurrence in flowers was more important during the night (27%) than during the day (12%) and, for daytime, during cloudy or windy than sunny conditions. It also varied depending on the exposure of floral tunnels. Visitation rates of both day-visiting Xylocopa and night-sheltering Eucera were negatively associated with an increase of the number of flowers per clump. No experimental evidence was found showing that the principal advantage for male bees to shelter in Iris flowers was to fly earlier in the morning.