Plant invasions in riparian areas of the Middle Danube Basin in Serbia

Riparian areas experience strong invasion pressures worldwide and represent important points of spread for invasive alien plants (IAPs) in the European mainland. The Danube Basin is a well-known point of high plant invasion levels. Given that the middle part of the Danube Basin is critically understudied and the general lack of data for Serbia, the study aimed to provide an insight into the spatial patterns of plant invasions in the riparian areas of Serbia (Middle Danube Basin area). A total of 250 field sites, distributed along 39 rivers (nine catchment areas) and six canal sections, were studied during a four-year period (2013–2016) for the presence and abundance of IAPs. At the landscape scale, we studied distribution patterns of IAPs, differences in invasion levels in different catchment areas and between rivers and canals. At the local scale, we investigated how the proximity to roads/railway lines, housing areas, different land-use types (primarily agriculture), and dominant vegetation on site related to invasion patterns. Of the 26 studied IAPs, those with a well-known weedy behavior, long history of cultivation and strong affinity for riparian areas prevailed in the study area. Riparian zones of the Danube catchment exhibited the highest invasion levels in terms of IAPs richness and abundance, followed by the catchment areas of the Timok, Sava and Zapadna Morava rivers. Surprisingly, the Danube-Tisa-Danube canal network had the lowest invasion level. At the local scale, agriculture in proximity of the field site and dominant vegetation on site were observed as significant predictors of the invasion level. On the other hand, proximity to roads/railway lines and housing areas was not related to the invasion level. Finally, our study provides the first systematic overview of IAPs’ distribution data for riparian areas of the Middle Danube Basin in Serbia, which could provide a basis for long-term monitoring of IAPs and development of future management plans.

Leaf trait differences between 97 pairs of invasive and native plants across China: effects of identities of both the invasive and native species

Many studies have attempted to test whether certain leaf traits are associated with invasive plants, resulting in discrepant conclusions that may be due to species-specificity. However, no effort has been made to test for effects of species identity on invasive-native comparisons. Here, we compared 20 leaf traits between 97 pairs of invasive and native plant species in seven disturbed sites along a southwest-to-northeast transect in China using phylogenetically controlled within-study meta-analyses. The invasive relative to the native species on average had significantly higher leaf nutrients concentrations, photosynthetic rates, photosynthetic nutrients- and energy-use efficiencies, leaf litter decomposition rates, and lower payback time and carbon-to-nitrogen ratios. However, these differences disappeared when comparing weakly invasive species with co-occurring natives and when comparing invasives with co-occurring widespread dominant natives. Furthermore, the magnitudes of the differences in some traits decreased or even reversed when a random subset of strongly to moderately invasive species was excluded from the species pool. Removing rare to common natives produced the same effect, while exclusion of weakly to moderately invasives and dominant to common natives enhanced the differences. Our study indicates that the results of invasive-native comparisons are species-specific, providing a possible explanation for discrepant results in previous studies, such that we may be unable to detect general patterns regarding traits promoting exotic plant invasions through multi-species comparisons.

Alien flora of Oman: invasion status, taxonomic composition, habitats, origin, and pathways of introduction

We present the first inventory and status assessment of the alien flora of Oman, mainly based on field data collected from 1998 to 2021. The study provides (i) a comprehensive account of alien vascular plant species occurring in the wild in Oman, with information on their taxonomic composition. For each species information is given on (ii) invasion status (casual, naturalized or invasive), biogeography, habitat and life-form characteristics, and pathways of introduction. Further, we (iii) explain the differences in the alien species composition in different parts of the country, and (iv) analyse the drivers of plant invasions in Oman. Out of the 111 alien species reported (7.7% of the total Oman vascular flora), 34 species are casuals and 77 naturalized; of the latter seven are considered invasive. The moderate number of alien plant species is likely a result of the country’s arid climate, with extremely high summer temperatures and low annual precipitation in most of its area, and the relatively long isolation of the country. The families richest in alien plant species are Fabaceae (17 species), Asteraceae (14 species) and Poaceae (12 species). More alien plants were found in northern Oman (82 species) than in southern Oman (60 species), and very few species are recorded from the central desert (7 species). The main habitats colonized were man-made habitats, either ruderal or agricultural. Most species alien to Oman are native to South America (49 species) or North America (43 species). This inventory provides a knowledge base for developing a national management strategy for alien vascular plants in Oman.

Enriched root bacterial microbiome in invaded vs native ranges of the model grass allotetraploid Brachypodium hybridum

Invasive species can shift the composition of key soil microbial groups, thus creating novel soil microbial communities. To better understand the biological drivers of invasion, we studied plant-microbial interactions in species of the Brachypodium distachyon complex, a model system for functional genomic studies of temperate grasses and bioenergy crops. While Brachypodium hybridum invasion in California is in an incipient stage, threatening natural and agricultural systems, its diploid progenitor species B. distachyon is not invasive in California. We investigated the root, soil, and rhizosphere bacterial composition of Brachypodium hybridum in both its native and invaded range, and of B. distachyon in the native range. We used high-throughput, amplicon sequencing to evaluate if the bacteria associated with these plants differ, and whether biotic controls may be driving B. hybridum invasion. Bacterial community composition of B. hybridum differed based on provenance (native or invaded range) for root, rhizosphere, and bulk soils, as did the abundance of dominant bacterial taxa. Bacteroidetes, Cyanobacteria and Bacillus spp. (species) were significantly more abundant in B. hybridum roots from the invaded range, whereas Proteobacteria, Firmicutes, Erwinia and Pseudomonas were more abundant in the native range roots. Brachypodium hybridum forms novel biotic interactions with a diverse suite of rhizosphere microbes from the invaded range, which may not exert a similar influence within its native range, ostensibly contributing to B. hybridum’s invasiveness. These associated plant microbiomes could inform future management approaches for B. hybridum in its invaded range and could be key to understanding, predicting, and preventing future plant invasions.

The Alien Plants That Threaten South Africa’s Mountain Ecosystems

The six major mountain ranges in South Africa support critically important ecosystem services—notably water production—and are rich in biodiversity and endemism. These mountains are threatened by detrimental land uses, unsustainable use of natural resources, climate change, and invasive alien plants. Invasive alien plants pose substantial and rapidly increasing problems in mountainous areas worldwide. However, little is known about the extent of plant invasions in the mountains of South Africa. This study assessed the status of alien plants in South African mountains by determining sampling efforts, species compositions and abundances across the six ranges in lower-and higher-elevation areas. Species occurrence records were obtained from three databases that used various approaches (roadside surveys, citizen science observations, focused botanical surveys). Most mountain ranges were found to be undersampled, and species composition assessments were only possible for two ranges. The majority of abundant alien plants in both the lower- and higher-elevation areas were species with broad ecological tolerances and characterised by long distance seed dispersal. These prevalent species were mostly woody plants—particularly tree species in the genera Acacia, Pinus, and Prosopis—that are contributing to the trend of woody plant encroachment across South African mountains. We suggest improved mountain-specific surveys to create a database which could be used to develop management strategies appropriate for each mountain range.

Alien (invasive) vascular plants in Slovakia – a story of successful plant immigrants

This article summarises the history of research into alien plants and plant communities in Slovakia (Central Europe). Earlier periods are reviewed briefly with reference to literature sources dealing with those periods more comprehensively. A milestone in the research was the publication of the Inventory of the alien flora of Slovakia in 2012 with a complete list of alien vascular plants. The last ten years are discussed more extensively in the article in four sections devoted to i) newly found alien plants, ii) distribution and habitat relations, iii) plant invasions, iv) citizen science based on the comprehensive excerption of literature sources. A list of 51 newly published alien taxa within the last ten years is also included with information on the year of their first occurrence in the wild in Slovakia.

Non-Native Herbivores Promote Plant Invasions Away From Mountain Roads in the Andes

While the role of environmental filters, usually described by elevation as proxy, and anthropogenic disturbance as drivers of non-native plant diversity and abundance in mountains have been extensively studied, the impact of herbivores are less explored. Livestock grazing can facilitate the introduction of non-native species by seed dispersal and reduce biotic resistance due to consumption and trampling of native plants, even in the highest protected areas in the Andes. We here explored the effects of elevation, livestock and distance to the road on non-native and native plant distributions. Our results confirm the largely negative relationship of non-native plant richness and cover with elevation, with a peak in richness and cover at low to intermediate elevations. Similarly, we show a strong decline in non-native richness with increasing distance to the road, especially at low elevations, accompanied by a strong negative effect of roads on native species richness. Most importantly, however, we show that the presence of non-native herbivores greatly increases the cover of non-native species away from the roadside, identifying herbivore disturbance as a potential catalyst of non-native plant invasion into natural vegetation of high-Andean protected areas. Our results confirm the often-shown role of disturbance as driver of plant invasions in mountains, yet highlight the interactive effects of disturbance by roads and herbivory: roads funnel non-native species towards higher elevations, while non-native herbivores can promote non-native plant success away from the roadside and into the natural vegetation. Hence, regulating soil and non-native herbivory disturbance is important for minimizing plant invasions at high elevation in the Arid Andes.