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The status (weed or beneficial shrub) of Chromolaena odorata in West Africa has been a major subject of debate since its introduction in the 1930s. Its negative impacts on agriculture and biodiversity are clear. However, indigenous people have harnessed several benefits of the plant, making management strategies less straightforward. Using indigenous voices in Ghana, the current perceptions of C. odorata in West Africa were assessed. Here, 90 respondents in three regions of Ghana were interviewed, using questionnaires, on aspects relating to the abundance, perceptions and management of C. odorata in their communities. Overall, results showed that the density of C. odorata had declined. The majority of the respondents considered C. odorata as a fallow shrub, a medicinal plant or both. However, impacts on crop production and injuries incurred during physical control were also highlighted. The local uses of the plant in Ghana included treating fevers and injuries, and as a fallow shrub for soil nutrient replenishment. Although most of the respondents classified C. odorata as a useful shrub in Ghana, they also highlighted the use of local farming tools such as cutlasses for the slash of the plant. The use of herbicides for the control of C. odorata was rare and not applied specifically for C. odorata. In conclusion, local awareness programmes on the deleterious impacts of C. odorata on ecosystem functioning and livelihoods are required for its effective management in West Africa. [ABSTRACT FROM AUTHOR]

Summary: Drosera L. (Droseraceae) is a genus of insectivorous plants distributed worldwide with 240 species, 40 of which are found in South America. In the temperate forests of Chile and Argentina the only species present is D. uniflora. In a peat bog in Nahuel Huapi National Park, Argentina, a new species of Drosera was found in February 2018. To identify the species, we used morphological characters, and in addition, we sequenced two individuals for the nuclear region ITS and the chloroplast gene rbcL. Other Drosera sequences for these molecular regions were downloaded from GenBank, and a phylogenetic analysis was done to confirm the morphological identification of the Patagonian individuals. Morphologically and genetically, the species found in Nahuel Huapi is D. rotundifolia, a mostly Northern Hemisphere species. This is an alien species to the region and is thought to have been transported to the bog by tourists that visit the area. The presence of an exotic species represents a threat to this particular ecosystem with high conservation value. Currently, the National Park is taking control actions order to remove all individuals of the recently detected species. This study represents the first report of an alien species of Drosera in southern South America growing in the wild. This potentially invasive species may not only have negative impacts on the natural peat bog habitats in southern Argentina and Chile, but may also reach bogs in other temperate parts of the world. [ABSTRACT FROM AUTHOR]

Summary: Exotic plants can compete well with native species because many invasive species are considered better nutrient users in both low‐ and high‐resource environments. However, whether invasive plants can outperform native plants at all stages of invasion is not very clear. We investigated the nitrogen (N), phosphorus (P) and N:P homeostasis of an invasive Eupatorium adenophorum and a co‐occurring native plant Artemisia argyi in an area across the five invasion stages of E. adenophorum. The N homeostasis (HN) of E. adenophorum was higher than that of A. argyi, whereas the P and N:P homeostasis (HP and HN/P) were higher for A. argyi. For E. adenophorum,HN decreased, but HP and HN/P increased with the invasion time. For A. argyi,HN/P increased, HP and HN remained stable with the invasion time. The results demonstrated that E. adenophorum could maintain higher HN during invasion stages when N was limited and could maintain higher HN and HP at invasion stages when P was more limited. This rapid nitrogen and phosphorus homeostasis transformation of invasive E. adenophorum during its invasion stages guarantees its stronger competitive ability over native species and promotes its invasion success. [ABSTRACT FROM AUTHOR]

Summary: Plant eradication is difficult, particularly in remote, protected areas. The Southern Ocean Islands are very isolated and highly protected, but the flora contains many alien plants. Small restricted populations have been eradicated, but eradication of established species has proven difficult. A better understanding of the efficacy of control methods at sub‐Antarctic temperatures and their off‐target impacts may increase eradication success. With interest in controlling non‐native Poa annua in the region, we aimed to determine if physical and chemical methods can control P. annua (the sub‐Antarctic biotype) in sub‐Antarctic conditions and examined their impact on native plants. We quantified the effectiveness of physical control methods on P. annua in situ on sub‐Antarctic Macquarie Island through field‐based experiments and assessed their selectivity on P. annua compared with native grasses. We also quantified the effectiveness of several herbicides on P. annua at sub‐Antarctic temperatures and assessed their selectivity on native grasses. Of the four physical disturbance methods tested, none effectively reduced P. annua cover as one‐off treatments. Of the herbicide treatments, glyphosate and trifloxysulfuron sodium were effective and were less damaging to native grass species, indicating potential selectivity. Physical control was of limited effectiveness, but did not affect native species richness. An integrated weed management programme utilising the strategic use of selective herbicides with follow‐up chemical and physical intervention may balance control and biodiversity outcomes. This research highlights the importance of site‐specific testing of control methods and understanding off‐target impacts of control when managing alien plant species in protected areas. [ABSTRACT FROM AUTHOR]

Summary: This work characterises the changes in composition of the weed flora commonly associated with certain south‐eastern Algerian crops over a 20‐year period. Vegetation sampling was carried out between 1990 and 2010 in three 1 ha date palm plantations that do not have understory crops, six 400 m² glasshouses used for market gardening and three 30 ha cereal centre‐pivot irrigation plots. In total, 162 species belonging to 40 families were recorded. As in many other agroecosystems around the world, the dominant families were Poaceae, Asteraceae, Brassicaceae and Amaranthaceae representing 45.1% of the species identified. The weed communities were characterised by a set of species from various origins: species with biregional, triregional and multiregional origins, and Saharo‐Arabian and Mediterranean species were particularly well represented. Overall, the most common weed species were as follows: Chenopodium murale, Lolium multiflorum, Melilotus indicus, Lysimachia arvensis, Sonchus oleraceus, Setaria verticillata, Polypogon monspeliensis and Erigeron canadensis, all of which are therophytes. The weed flora differed among the three sampled agroecosystems, which is to be expected, as their respective management sequences are quite different. Weed monitoring over the 20 years showed that weed composition changed over time, particularly in the palm plantations and the cereal plots. For a better understanding of the drivers of weed composition and changes over time and better weed management, studying weed provenance (crop seed purchase and organic fertilisation) as well as agricultural practices is necessary. [ABSTRACT FROM AUTHOR]

Invasive plants can seriously threaten biodiversity and ecosystem function. Thus, controlling the abundance and mitigating the deleterious effects of invasive plants is imperative. The effectiveness of removal methods could vary based on potential damage to non-target species and on the ecological context of invasion. For example, species-poor communities might benefit disproportionately from invasive removal because they tend to be more heavily invaded than species-rich communities. In this study, we tested the efficacy of two common methods of invasive plant control, hand removal and 2,4-D herbicide application, against the invasive forb, Galium verum. We further tested whether the community response to G. verum removal varied across communities that differed in native grass richness (one, three or six species) and composition. Grass diversity did not interact with G. verum removal to influence any response. Instead, hand removal and herbicide application each reduced G. verum stem density by >50% relative to controls. Furthermore, hand removal of G. verum increased species richness by 25% relative to controls and herbicide-sprayed plots. Despite this benefit, hand removal is labour-intensive and impractical for large areas. These results also suggest that applying herbicide may control G. verum spread without substantially reducing forb diversity in invaded tallgrass prairie. Thus, herbicide application may be most suitable for grasslands with low native forb diversity, especially in managed grasslands and pastures where maintaining native forb diversity is a lower priority than maintaining high grass productivity. [ABSTRACT FROM AUTHOR]

Ludwigia grandiflora (water primrose), a native to the Americas, is one of the most important invasive alien aquatic plants in Europe. In Germany, a first population was found in an oxbow lake of the River Leda in Lower Saxony, north-western Germany, in 2004. Ludwigia grandiflora formed both dense monospecific patches and mixed stands with native plants. A study on the biology of L. grandiflora documented that the plants regrow in spring from vegetative means only, even though viable seed production occurred. Hand weeding was successfully tested in different sampling sites as a sustainable management tool and subsequently used for the management of this species. Within 3 days, more than 99% of the biomass (25 tonnes of fresh mass) was harvested in 2013. Afterwards, a one-day post-treatment in the same year, two-one-day treatments in 2014 and one-one-day treatment in 2015 were made to harvest the regrown plants. After the first year, plant regrowth occurred only in one extremely muddy site, while in more than 99% of the water body, L. grandiflora was eradicated. Even though L. grandiflora was not completely eradicated from the water, a total eradication seems achievable within the next few years. The study documented the difficulties in the management of aquatic weeds, particularly in heterogeneous habitats with varying sediment structure. Management measures must be adapted to the infested habitat and species biology, which is mandatory for successful management of all aquatic weeds. [ABSTRACT FROM AUTHOR]

The objective of this study was to verify the origin of and resulting floristic composition from seedbanks in different agroforestry systems in Tomé-Açu, Brazil. The seedbanks were sampled in three smallholder farmers (Demonstration Units = DU), each with three agroforestry treatments and secondary forest as control. Seedling emergence in a glasshouse was used to quantify and identify the seeds collected in 2008. The floristic composition of the above-ground community was characterised with annual floristic surveys from 2008 to 2011. The total densities and diversity of the seedbanks were not different among the treatments within a given DU, but differences occurred among DU. The most abundant woody species had higher seed densities in the secondary forests than in DU. Conversely, among the herbaceous species, two groups were differentiated: species with similar densities between the DU and the secondary forest and species with higher density in the DU. In the DU, the similarity between the floristic composition of the seedbank and the flora surveyed in 2008 was high, but decreased in subsequent years. The species present in the seedbank of agroforestry systems are highly influenced by the secondary forest, but provide little information about the floristic composition that will arise in the future. [ABSTRACT FROM AUTHOR]

Impatiens glandulifera is one of the most widespread invasive plant species in the UK. Although aspects of its biology are known, there is little information about its association with microbial communities, both above ground and below ground. Furthermore, it is unknown whether this species exhibits any form of plant-soil feedback ( PSF), commonly seen in other invasive weeds. We conducted a PSF experiment, in which plants of I. glandulifera were grown in soil that supported the species and compared with plants grown in a control soil from the same locality. Soil nutrients were measured, and the soil and foliar microbial communities were assessed. Impatiens glandulifera grew larger and faster in conditioned soil compared with the control. Higher levels of phosphate were also found in conditioned soils. Arbuscular mycorrhizal fungal ( AMF) colonisation was lower in conditioned soils, suggesting that I. glandulifera may rapidly alter AMF communities in invaded areas. PSFs had a significant effect on the foliar endophyte community, with clear separation of species between conditioned and control soils. These results show that I. glandulifera displayed a positive PSF and the PSF mechanism extended beyond the soil microbial community to affect foliar endophytes. The observed increase in endophytes in plants grown in conditioned soil could enhance resistance to herbivory, thus further accentuating the invasive properties of this species. [ABSTRACT FROM AUTHOR]

There is a need for management strategies to control dominant perennial weeds and restore seminatural communities. We compared the effects of five weed control treatments on dense Pteridium aquilinum relative to an untreated experimental control over an 8-year period with the aim of restoring acid grassland. The weed control treatments tested were as follows: cutting and bruising, both twice and thrice annually, and herbicide treatment (asulam in year 1 followed by annual spot retreatment of all emergent fronds). Pteridium aquilinum performance and plant species composition were monitored. Data were analysed using Bayesian mixed-effect models and multivariate techniques. Cutting twice and thrice yearly and the asulam treatment all reduced frond density to zero; both bruising treatments were ineffective. The plant communities in the cut and asulam-treated plots showed differences from the untreated and bruised plots; the asulam-treated plots contained more ruderal species and the cut plots were more typical of acid grassland. Acid grassland recovery was fastest in the asulam-treated plots, but the cut plots caught up after approximately 5 years. There were two important conclusions. First, an intractable weed like P. aquilinum can be eradicated and a vegetation more suited for grazing can be achieved by the continuous application of some treatments over many years. Here, success was achieved by cutting twice/thrice annually, or by a single asulam application followed by annual spot spraying of all emergent fronds for 8 years. Second, bruising, a treatment favoured by some conservation organisations, did not work and cannot be recommended. The use of long-term, continuously applied treatments might be considered for all perennial weeds with large underground root/rhizome systems. [ABSTRACT FROM AUTHOR]

Phenological shifts may play an important role in the success of invasive species. In the coastal regions of continental Portugal, Acacia longifolia is one of the most widespread invasive plants, but there are significant gaps in our understanding and interpretation of its phenology. This study is the first to investigate the phenological variation of A. longifolia and its association with climate in populations representing a temperature and precipitation gradient in mainland Portugal. The results highlighted significant variations in the vegetative (leaf initiation) and reproductive phenophases (bud formation, flowering and fruiting) among populations. Overall, leafing was observed throughout the year, bud formation occurred between summer and spring, anthesis between late winter and the beginning of spring, and fruiting started in late winter. Most of the reproductive phenophases varied across elevation or latitudinal gradients, with populations that were subjected to more stressful climatic conditions advancing their flowering and fruiting phenophases. The occurrence of each phenophase was strongly associated with the climatic conditions in the previous 5-12 months, suggesting that plants receive their phenological cues well in advance of their phenological response. Among climatic factors, temperature and irradiance were the most significant predictors of the phenological cycle of A. longifolia, but precipitation also exerted a greater influence on budding and flowering of the species. The phenological response of A. longifolia in a variety of sites represents an important step towards understanding how its phenology may react to the projected climate change in the Mediterranean region. [ABSTRACT FROM AUTHOR]

Portulaca oleracea, an r-strategist, is one of the world's most troublesome weeds. During hot seasons, P. oleracea frequently becomes monodominant in choy sum (Brassica parachinensis) fields in Guangzhou city, southern China. Here, we studied the seasonal dynamics of P. oleracea's germinable soil seedbank, population density and above-ground biomass in choy sum fields that had been cultivated continuously for several years. Using P. oleracea seeds collected from these fields, we tested seed dormancy, survival and germination, seedling growth and generation time. Portulaca oleracea occurred at high levels during the hot season, but its occurrence was low, and the germinable soil seedbank was much greater during the cold season. The weed's opportunistic characteristics allowed it to avoid freezing and to proliferate during optimal conditions. Portulaca oleracea's generation time was very flexible, as short as 31 days during the hot season, but longer than 100 days during the colder season. Seed dormancy tended to be shorter when the seeds were stored at a higher temperature. At a temperature of 35°C, both seed germination and seedling growth showed advantages over those of choy sum. Storage for one year at a temperature of -20°C or burial in a paddy field did not significantly reduce P. oleracea seed germination. Nevertheless, seed storage at a temperature of 15°C and soil coverage of 0.5 cm on top of the seeds significantly constrained seed germination. 'Stale seedbed' and/or coverage of the surface with soil are recommended during the hot season. However, rotation of rice and upland crops is not an efficient method for managing Portulaca oleracea infestation. [ABSTRACT FROM AUTHOR]

Solidago canadensis is native to North America, but has become a noxious invasive plant in China. We know only a little about its invasion history and the effects of introductions on its genetic composition. Here, we investigated genetic variation and structure between 15 North American and 13 Chinese populations of S. canadensis using AFLP makers. Four AFLP loci suggested relatively high genetic diversity of this weed and similar genetic variation between the invasive range and the native range. Most genetic variation was within populations across two ranges, but the Chinese range had a higher degree of among-population variation than the North American range. Multiple tests, including Bayesian assignment, UPGMA analysis, PCoA and analysis of 'isolation by distance', showed that the Chinese populations originated from at least two distinct native sources and that secondary introduction or dispersal should be common in China. Also, North American populations were possibly a single genetic group. Overall, S. canadensis in China was probably founded from multiple introductions and then spread through long-distance dispersal associated with human activities. Genetic variability in the species in the invaded range appears to have favoured establishment and spread and may well provide a challenge to successful control. [ABSTRACT FROM AUTHOR]

Ventenata dubia ( African wiregrass), a winter annual weed, is a non-native species invading grasslands, rangelands and pastures throughout the USA. Limited information is available on its suitability as a host to pathogens and insects in its invaded range. The barley/cereal yellow dwarf virus ( B/ CYDV) complex occurs ubiquitously in Poaceae species. In non-managed grasslands, BYDV infection influences competitive dynamics between native and invasive grasses and facilitates invasion by non-native annual weeds. The Palouse prairie of south-eastern Washington and northern Idaho, USA, is an endangered ecosystem. Surveys of V. dubia in Palouse prairie and neighbouring Conservation Reserve Program ( CRP) habitats were conducted to determine whether B/ CYDV viral species are present. Laboratory tests examined the suitability of V. dubia to host BYDV - PAV and serve as an inoculum source. Plant growth and weight parameters were measured to gauge the impact of BYDV- PAV on V. dubia. Infection of V. dubia in Palouse prairie and CRP habitats with two species of BYDV, PAV and SGV, was detected for the first time. The ability of BYDV- PAV to infect V. dubia in the laboratory and transmission from infected V. dubia to barley were demonstrated. BYDV- PAV-infected V. dubia showed reductions in plant height, number of leaves and tillers per plant, and above-ground dry weight, suggesting that V. dubia is sensitive to BYDV. Results demonstrate that V. dubia is a host to BYDV and may serve as a virus inoculum source with potential implications for its management, competitive dynamics between invasive and native grasses and future conservation of endangered grasslands. [ABSTRACT FROM AUTHOR]

Understanding how plant species with similar resource requirements co-exist has been a long-standing ecological question with several theoretical explanations. One potential mechanism is the storage effect hypothesis. According to this hypothesis, species co-exist because they differ in when they are most actively using resource and, therefore, respond differently to environmental perturbation. The hypothesis is based on two main assumptions: (i) two competitors have different responses to climate and (ii) the responses to climate are mediated by changes in the relative importance of intra- and interspecific competition. The hypothesis could provide useful insights into the role of climate in maintaining weed species diversity and potential shifts in dominant species under climate change. This study tested the basic principles of the storage effect hypothesis on weed communities using data from the Broadbalk long-term fertiliser experiment. Relative abundance of weeds in 10 plots with contrasting fertility but no herbicides was assessed for 21 years. Multivariate analyses and generalised additive mixed models were used to analyse the data. The following pairs of species were found to be adapted to similar fertiliser levels, but diverged in their response to climate: (i) Papaver rhoeas-Tripleurospermum inodorum, (ii) Medicago lupulina-Vicia sativa and (iii) Scandix pecten-veneris-Ranunculus arvensis. Contrasting responses to spring temperature within these species pairs modified the competition balance providing evidence for the storage effect hypothesis and helping to explain weed co-existence in the Broadbalk experiment. [ABSTRACT FROM AUTHOR]

Biological invasions and climate warming are two major threats to the world's biodiversity. To date, their impacts have largely been considered independently, despite indications that climate warming may increase the success of many invasive alien species. We therefore set up an experiment to study competition between native and invasive alien plant species and the effects of climate warming thereon. Two highly invasive alien plant species in Belgium, each with a native competitor that dominated in invaded sites, were grown either together (1:1 mixtures) or in isolation (monocultures) at ambient and elevated temperature (+3°C) in climate-controlled chambers. To detect possible mechanisms underlying the effects of competition and elevated temperature, we conducted a combined growth and nitrogen uptake analysis. In one pair, Senecio inaequidens - Plantago lanceolata (alien invasive - native), the alien species dominated in mixture, while in the other pair, Solidago gigantea - Epilobium hirsutum, the native species dominated. Climate warming reduced the invader dominance in the first species pair, but stimulated the suppressed invader in the latter. Many of the biomass responses for these two species pairs could be traced to the root-specific nitrogen uptake capacity. The responses of the native-invasive interaction to warming could not always be extrapolated from the monoculture responses, pointing to the necessity for experiments that take into account species interactions. [ABSTRACT FROM AUTHOR]

This study corrected the misidentification of an alien species, Salvia tiliifolia, which had been incorrectly identified as S. dugesii (a synonym of S. melissodora) in China. The distribution of S. tiliifolia in China was surveyed and it was inferred that it was probably introduced into Kunming, Yunnan in the 1990s and then spread to adjacent counties of Yunnan and south-western Sichuan Province. The Australian weed risk assessment ( WRA) was used to evaluate its invasive status. To determine the validity of Australian WRA in China, another 25 exotics representing casual alien plants, naturalised plants and invasive plants were tested. The Australian WRA was validated as a legitimate approach in China. Salvia tiliifolia scored 14, falling into the category of invasive plants. While the distribution of S. tiliifolia is currently restricted to Yunnan and a small part of Sichuan and the species has not displayed an adverse impact on local environments yet, the WRA results indicated that the species was a high risk plant. It was recommended that local land managers should monitor this species and take measures to stop its continuing expansion or eradicate it if possible. [ABSTRACT FROM AUTHOR]

Solanum elaeagnifolium (silverleaf nightshade) is an invasive perennial weed in Australia, with aerial growth commencing in spring from either the perennial root system or the soil seedbank, with senescence occurring in autumn. A total of 642 S. elaeagnifolium individuals were collected at flowering from 92 locations in south-eastern Australia to study morphological variation and its implications for management. Large morphological variation was found between individuals from different locations. Leaf length, width and area ranged from 1.44 to 10.6 cm, 0.39 to 4.09 cm and 0.41 to 25.8 cm2 respectively. Plants from higher rainfall regions were significantly taller and had larger leaves, suggesting a possible correlation between rainfall and morphology. Scanning electron microscopy comparison of leaf surfaces showed lower trichome and stomatal densities on the adaxial surface (67.0 ± 3.3 trichomes mm−2 and 603.4 ± 29.2 stomata mm−2 respectively) than on the abaxial surface (131.9 ± 7.2 trichomes mm−2 and 813.7 ± 30.5 stomata mm−2 respectively). The morphological plasticity of S. elaeagnifolium highlighted in this study could probably contribute to its adaptability and partly explain its establishment and continuing expansion in Australia. [ABSTRACT FROM AUTHOR]

Soyabean ( Glycine max) was grown at ambient and projected levels of atmospheric carbon dioxide (+250 μmol mol−1 above ambient) over two field seasons with and without the presence of a weed, Abutilon theophrasti, to quantify the potential effect of rising atmospheric carbon dioxide concentration on weed-crop interactions and potential yield loss in soyabean. Under weed-free conditions, elevated CO2 resulted in stimulations in soyabean seed yield and associated components, including pod number. At an approximate density of 6 plants m−2, A. theophrasti competition resulted in a significant reduction (−40%) in soyabean seed yield. Although differences in seed yield reduction by A. theophrasti were observed as a function of year, the relative decrease in seed yield with A. theophrasti biomass did not differ in response to CO2. Although careful weed management will be necessary if CO2-induced increases in seed yield for soyabean are to be achieved, these data suggest that soyabean seed yield may be more resilient in competition with A. theophrasti as a function of rising atmospheric levels of carbon dioxide. [ABSTRACT FROM AUTHOR]