Urban areas are increasingly recognized as important centers of biodiversity. Nonetheless, invasive species can reduce this biodiversity, and cities can be hubs for alien plant invasions, highlighting the need to monitor urban biodiversity and problematic alien species. The goal of our study was to assess the distribution of wild chervil (Anthriscus sylvestris (L.) Hoffm.) and anise (Myrrhis odorata (L.) Scop.) in green spaces of Reykjavík, Iceland. This information is necessary to implement the city´s biodiversity strategy regarding invasive species. Both of these alien plants are spreading throughout Iceland, and Reykjavík´s high latitude (≥63° N) location and remoteness makes it an ideal case study to assess alien plant introductions and invasions in subarctic urban areas. We surveyed from May to October 2017 four green spaces (Laugarnes, Vatnsmýri, Elliðaárdalur, and Ægisiða), using AllTrailsPro and ArcGIS mobile applications. ANOVA and Bonferroni correction (post-hoc test) were used to compare the distribution and patch sizes of A. sylvestris and M. odorata among the study sites. We found that A. sylvestris covered at least 10% (15.5 ha) of the total area surveyed (158 ha), while M. odorata only covered ≤1 ha. Both plants were abundant near buildings, pathways, riversides, and streams, and they are expanding their distribution in Reykjavík´s green spaces. While A. sylvestris is clearly more established and widespread with larger patches (>100 m2), the distribution of M. odorata is more localized, occurring mainly in smaller patches (<100 m2). We recommend long-term monitoring to further assess M. odorata´s invasive potential, as well as testing and adopting integrated weed management strategies via adaptive management to control the distribution of A. sylvestris and that of other problematic alien plants. These actions, which are applicable to other subarctic cities, will help foster more proactive management encouraging urban biodiversity.

Little lovegrass, an annual species native to Europe, was not listed in the floras that describe the plants of Idaho and Washington. Twelve collections were made between 1984 and 1992 from four Idaho counties and six Washington counties. Those records extended the range of this species 450 to 1000 km northwest of populations reported in the literature. Approximately 600 km separated the furthest of the new collection sites, indicating widespread naturalization in those states. Eight of the collections were from roadsides, suggesting that human transport technology had a substantial influence on this plant's dispersal.

Two introduced windgrass species have become crop weeds in North America. Common windgrass is a major weed of winter cereals in Europe and was first documented in North America in the early 1800s. It is a weed of roadsides and waste areas in the northeastern United States and in winter grain fields of southern Ontario and Michigan. Interrupted windgrass was first reported in North America approximately 90 yr ago; it is adapted to more arid sites than common windgrass and is distributed predominantly in the northwestern U.S.A. During the past 10 to 15 yr, interrupted windgrass has adversely affected winter grain and grass seed producers in the Pacific Northwest due to additional control costs.

The increase in atmospheric CO2 levels can influence the growth of many invasive exotic plant species. However, it is not well-documented, especially for C4 plants, how these growth responses will alter the effectiveness of the world's most widely used herbicide for weed control, glyphosate. We aimed to address this question by carrying out a series of glasshouse experiments to determine if tolerance to glyphosate is increased in four C4 invasive exotic grasses grown under elevated CO2 in nonlimiting water conditions. In addition, traits including specific leaf area, leaf weight ratio, leaf area ratio, root : shoot ratio, total leaf area, and total biomass were measured in order to assess their contribution to glyphosate response under ambient and elevated CO2 levels. Three of the four mature grass species that were treated with the recommended concentration of glyphosate displayed increased tolerance to glyphosate under elevated CO2. This was due to increased biomass production resulting in a dilution effect on the glyphosate within the plant. From this study, we can conclude that as atmospheric CO2 levels increase, application rates of glyphosate might need to be increased to counteract the growth stimulation of invasive exotic plants.

Climate change, comprising an increase in carbon dioxide levels coupled with elevated temperature, may favor invasive plants, as they possess traits that will facilitate adaptation to a new climate. In particular, alien plants of subtropical origin introduced to a colder region are expected to increase the number and size of their populations and spread farther with climate change. Seedlings of three such woody alien species in New Zealand (Archontophoenix cunninghamiana, Psidium guajava, and Schefflera actinophylla) were grown in environmental chambers under the combination of two temperature (23.7 and 26 C [74.7 and 78.8 F]) and two CO2 (450 and 900 ppmv) regimes, simulating current conditions and conditions projected for the end of the century. Total biomass of S. actinophylla was 45% higher and total leaf area 35% larger under doubled CO2 compared to current CO2. Root : shoot ratio was higher under doubled CO2 across all species, and the number of branches was increased for P. guajava. The only significant interactive effect of elevated temperature and doubled CO2 was for relative growth rate of the height of S. actinophylla seedlings. This study provides strong evidence of more vigorous growth of S. actinophylla under future conditions, particularly increased CO2, whereas the other two species appear likely to maintain current growth rates. Better knowledge of the types of future conditions that may benefit such species, together with results of species distribution models and competition and eco-physiology studies will ensure robust weed risk assessments.

This paper reviews the biology of two closely related Mediterranean annuals, yellow starthistle and common crupina, which have invaded grassland, shrub steppe, and open woodland habitats in western North America. Despite the similarity of their winter annual life cycle, the two species differ significantly in population dynamics. Common crupina has traits that favor persistence rather than rapid population growth: large, heavy achenes with an after-ripening requirement; lower fecundity but higher germination success; and reproduction regulated by vernalization and photoperiod in addition to thermal time. Persistence traits also foster invasion of undisturbed or less degraded steppe habitats. Yellow starthistle has more ruderal traits: small, light, rapidly germinating achenes; higher fecundity, with greater seedling mortality; and reproduction that is less sensitive to photoperiod and vernalization. These characteristics confer a greater adaptability for rapid spread and colonization of disturbance by yellow starthistle than by common crupina. An understanding of the relative differences in biological characters of each species and in their function in invaded environments is relevant to ecological management of these pest species.

As part of a larger survey of biodiversity in private gardens in Sheffield, UK, we examined the composition and diversity of the soil seed banks in each of 56 gardens. Six soil cores from each garden revealed 2759 seedlings of 119 taxa, although the real species richness is likely to be much higher than this. By far the most abundant species were weedy natives, while the most common alien was Buddleja davidii. Seeds of perennial herbs were more abundant than hundreds of all other life forms combined. More frequent species were also more abundant, but the relationship was weak. Numbers of species in the seed bank and in the garden flora were positively but very weakly related. Seeds were quite evenly distributed between 0–5 cm and 5–10 cm soil layers, and most seeds were of species known to have persistent seed banks. Seeds of some species were largely confined to gardens in which the plant was growing, but others were not.