Urban sprawl facilitates invasions of exotic plants across multiple spatial scales

Exotic bees in urban ecosystems: establishment, impact, and potential for invasion

Native bee species decline has sparked extensive research and conservation efforts, particularly in urban areas where initiatives and interventions aim to restore native bee populations. Paradoxically, these same urban interventions may inadvertently support non-native bee species, fostering the establishment of thriving exotic populations. Exotic bees often thrive in urban environments where advantageous traits, such as cavity-nesting and high reproductive plasticity, combine with human activities that intentionally and unintentionally facilitate their introduction and spread. Although many exotic species remain benign, others may transition to invasive status, leading to competition with native bees, the spread of diseases, and interference in biodiversity assessments. This review synthesizes current knowledge on how urbanization impacts exotic bee establishment and assesses potential pathways for these species to become invasive.

Effects of laundry washing on germination of cloth-dispersed seeds depends on washing intensity not on detergent type

Unintentional human-vectored seed dispersal (HVD) occurs when the seed dispersal vectors are humans, and the seeds are attached to clothing or footwear during various outdoor activities. Since most plant species spread by HVD are invasives or weeds, the process can have globally relevant adverse environmental effects due to the growing global tourism industry. Here we evaluated whether the germination capacity of seeds can be reduced by laundry washing treatments used in households, in order to decrease the chance of unintended dispersal of plant species by clothing. We experimentally tested the effects of seven types of detergents with different chemical composition and three washing intensities in a full factorial design on the germination capacity of 18 plant species. Washing at high intensity (60 °C) significantly decreased the germination capacity in 15 species, probably due to high temperatures and longer exposure times. Washing at low (30 °C) and medium intensities (40 °C) had no effect. Detergent type affected the germination capacity of only three species. The findings underscore the importance of laundry washing in seed dispersal, since the low and medium washing intensities and detergent types that are commonly used in households do not decrease the germination capacity of the cloth-dispersed seeds. We urge addressing the spread of HVD-dispersed seeds through combined biosecurity measures. Self-regulation, such as removing of seeds from clothes and disposing them properly, is crucial. Informing outdoor workers, who play the largest role in HVD, can encourage small behavioural changes to decrease the adverse effects of this process.

Green infrastructure design for the containment of biological invasions. Insights from a peri-urban case study in Rome, Italy

Secondary shrublands and transitional woodland/shrub formations are recognised to be particularly susceptible to plant invasions, one of the main global threats to biodiversity, especially in dynamic peri-urban landscapes. Urban fringes are in fact often the place for the sprawl of artificial surfaces, fragmentation of habitats, and complex land transitions (including both agriculture intensification and abandonment), which in turn increase propagule pressure of exotic species over residual semi-natural ecosystems. Within this framework, the present study was aimed at analysing i) how landscape composition and configuration affect the richness of woody exotic species in shrubland and transitional woodland/shrub patches, and ii) how this threat can be addressed by means of green infrastructure design in a peri-urban case study (Metropolitan City of Rome, Italy). Accordingly, the occurrence of exotic plants was recorded with field surveys and then integrated with landscape analyses, both at patch level and over a 250 m buffer area around each patch. Thus, the effect of landscape features on exotic plant richness was investigated with Generalised Linear Models, and the best model identified (pseudo R-square = 0.62) for inferring invasibility of shrublands throughout the study area. Finally, a Green Infrastructure (GI) to contain biological invasion was planned, based on inferred priority sites for intervention and respective, site-tailored, actions. The latter included not only the removal of invasive woody alien plants, but also reforestation and planting of native trees for containment of dispersal and subsequent establishment. Even though specifically developed for the study site, and consistent with local government needs, the proposed approach represents a pilot planning process that might be applied to other peri-urban regions for the combined containment of biological invasions and sustainable development of peripheral complex landscapes.

Spatiotemporal evolution of habitat quality and its response to landscape patterns in karst mountainous cities: a case study of Guiyang City in China

Habitat quality heterogeneity is one of the concrete manifestations of landscape pattern changes caused by human activities, which is of great significance to improve habitat quality by optimizing landscape pattern, thus scientifically protecting biodiversity and promoting ecological civilization construction. The coupling of rapid urbanization and ecological restoration measures has had a significant influence on the habitat quality of fragile and fragmented karst mountainous cities in recent years. In this study, spatiotemporal dynamics and heterogeneity of habitat quality and the impact of landscape patterns on habitat quality are analyzed in Guiyang, a typical karst mountain city in southwest China, mainly using the key methodologies such as the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) model, Exploratory Spatial Data Analysis (ESDA), and hierarchical partitioning (HP). We found that the habitat quality index of Guiyang City improved from 0.6643 to 0.6988 during 2000-2019; the distribution of habitat quality has significant spatiotemporal heterogeneity and spatial aggregation effect with the low values or the decreased areas concentrated in and around the built-up areas or urbanization expansion areas. Landscape composition had greater contribution than landscape configuration to habitat quality. The increased areas of natural habitat have had a positive effect on habitat quality. Moreover, each landscape configuration had a significant positive or negative correlation with the habitat quality. Therefore, implementing ecological protection and restoration measures in karst mountainous cities might be an effective strategy to improve habitat quality during rapid urbanization. Furthermore, optimizing habitat patterns, reducing the habitats loss, and protecting the natural habitat integrity are crucial to improving and maintaining biodiversity in the study area.

Impacts of land use change on native plant-butterfly interaction networks from central Mexico

Background

Land use change is a key catalyst of global biodiversity loss and ecosystem degradation. Deforestation and conversion of natural habitats to agricultural or urban areas can profoundly disrupt plant-flower visitor interactions by altering their abundances and distribution. Yet, specific studies analyzing the effects of land use change on the structure of networks of the interactions between particular groups of flower visitors and their plants are still scarce. Here, we aimed to analyze how converting native habitats affects the species composition of butterfly communities and their plants, and whether this, in turn, leads to changes in the structure of interaction networks in the modified habitats.

Methods

We performed bi-monthly censuses for a year to record plant-butterfly interactions and assess species diversity across three habitat types, reflecting a land-use change gradient. From original native juniper forest to urban and agricultural zones in central Mexico, one site per land use type was surveyed. Interactions were summarized in matrices on which we calculated network descriptors: connectance, nestedness and modularity.

Results

We found highest butterfly diversity in native forest, with the most unique species (i.e., species not shared with the other two sites). Agricultural and urban sites had similar diversity, yet the urban site featured more unique species. The plant species richness was highest in the urban site, and the native forest site had the lowest plant species richness, with most of the plants being unique to this site. Butterfly and plant compositions contrasted most between native forest and modified sites. Network analysis showed differences between sites in the mean number of links and interactions. The urban network surpassed agriculture and native forest networks in links, while the native forest network had more interactions than the agriculture and urban networks. Native plants had more interactions than alien species. All networks exhibited low connectance and significant nestedness and modularity, with the urban network featuring the most modules (i.e., 10 modules).

Conclusions

Converting native habitats to urban or agricultural areas reshapes species composition, diversity and interaction network structure for butterfly communities and plants. The urban network showed more links and modules, suggesting intricate urban ecosystems due to diverse species, enhanced resources, and ecological niches encouraging interactions and coexistence. These findings emphasize the impacts of land use change on plant-butterfly interactions and the structure of their interaction networks.

Influences of environment, human activity, and climate on the invasion of Ageratina adenophora (Spreng.) in Southwest China

With economic and social globalization, invasive alien species have significantly threatened local ecological security. Identifying the invasive mechanisms of invasive alien species can aid in preventing species invasions and protecting local ecological and economic security. As a globally invasive plant, Ageratina adenophora (Asteraceae) has spread to many parts of the world and had a seriously impacted the ecology and economy of its invaded areas. Using observational data and Landsat OLI images in an arid valley region in southwest China, this study examined how climate, human activity and environmental factors influence the invasion of A. adenophora and its underlying mechanism. Our results showed that the invasion abundance of A. adenophora was significantly affected by environmental factors (the relative importance was 87.2%), but was less influenced by human activity and climate factors (the relative importance was 2% and 10.8%, respectively). The A. adenophora abundance significantly decreased with aspect, community canopy density, shrub layer coverage, herb layer coverage, Simpson diversity index of shrub and herb layers, the shortest distance to residential areas and temperature seasonality, whereas it increased with soil moisture, temperature annual range, precipitation of wettest month and precipitation of driest month. We conclude that biotic competition is the most influential factor in the invasion of this plant in the arid valley regions. Our results are of great significance for invasion prevention and forest conservation and management in southwest China. Our work emphasized that optimizing the community structure, such as by increasing canopy and shrub coverage and species biodiversity, may help control and mitigate the A. adenophora invasion in southwest China.

Land-use diversity can better predict urban spontaneous plant richness than impervious surface coverage at finer spatial scales

Urban spontaneous plants, that are not intentionally propagated by humans and do not belong to the remnants of the natural habitats, not only occur in green spaces but are also distributed in diverse microhabitats in impervious surface areas. Impervious surface coverage is commonly used in studies on spontaneous plant diversity patterns in human-dominated landscapes; however, the role of habitat diversity (i.e., land-use diversity) has been overlooked. Here, we surveyed spontaneous plant composition and land uses (12 types) in 321 0.25 ha sampling sites on the Chongming District islands, Shanghai, to determine the role of land-use diversity in explaining species richness. We examined the linear relationships between species richness and land-use diversity, and quantified the importance of impervious surface coverage and land-use diversity using the random forest (RF) method. All these analyses were conducted for spatial scales from 0.25 to 5 ha in 0.25 ha increments. We found an overall positive relationship between species richness and land-use diversity, and the RF model predicted approximately 50% of the species richness variation at the smallest spatial scale. However, the positive relationship weakened with spatial scale increase, and a rapid decline in explanatory power occurred for all predictor variables in the RF model. Besides impervious surface coverage, both the vegetated and non-vegetated land-use diversity contributed substantially to the prediction of species richness at finer spatial scales. The findings clarify how land-use diversity, both in green spaces and impervious surface areas, affect urban spontaneous plant richness and should be considered in urban biodiversity conservation strategies at the neighborhood scale.

The invasion history of Elodea canadensis and E. nuttallii (Hydrocharitaceae) in Italy from herbarium accessions, field records and historical literature

We analysed the invasion history of two North American macrophytes (Elodea canadensis and E. nuttallii) in Italy, through an accurate census of all available herbarium and field records, dating between 1850 and 2019, and a rich literature collection describing the initial introduction and naturalisation phase that supports the results obtained by the occurrence records. Elodea canadensis arrived in Italy before 1866 and had two invasion phases, between the 1890s and 1920s and between the 1990s and 2000s; E. nuttallii, probably arrived in the 1970s, started invading in 2000 and the invasion is still ongoing. Botanical gardens and fish farming played a crucial role in dispersal and naturalisation of both species. The current invasion range of both species is centred in northern Italy, with scattered occurrences of E. canadensis in central and southern regions. River Po represents a dispersal barrier to the Mediterranean region and a strategic monitoring site to prevent the invasion in the peninsula. The study detects differences in the niches of the two species during the introduction and naturalisation phase and a habitat switch occurred after 1980 in E. canadensis and after 2000 in E. nuttallii, during their expansion phases. For E. canadensis the switch corresponds to the second invasion round. Further research can clarify whether the second invasion round is due to confusion of the recently introduced E. nuttallii with E. canadensis, to a cryptic introduction of a new genotype, to post-introduction evolution, or just to an increased scientific interest in biological invasions.

Connectivity, landscape structure, and plant diversity across agricultural landscapes: novel insight into effective ecological network planning

Natural habitats in rural and urban areas are increasingly fragmented and altered by human impacts that are limiting the animal and plant dispersal process. Fragmentation and isolation can be reversed by restoring landscape connectivity through effective Ecological Network (EN) planning. However, most of the studies analyzing the influence of connectivity and landscape structure on biodiversity are focused on animals, while the understanding of their interplaying role on plant diversity remains limited. We studied the relationships between α and β diversity pattern and landscape structure and connectivity in the nodes of an EN developed in agricultural landscapes, as a part of regional landscape planning framework in Friuli Venezia Giulia region (North-East of Italy). As an innovation, the study aims at parsing the interacting effect of landscape structure, surrounding habitats and nodes, and structural connectivity on EN plant diversity at two specific scales of investigation i.e., the habitat and the node scale. The habitat was the basic ecological unit, while the node was the basic cartographical unit for the EN mapping (multi-habitat or mono-habitat nodes). A total of 443 plant species were collected across 219 sample plots, in 14 different habitats and 87 nodes of the EN. We found that high node connectivity leads to higher species richness (α-diversity) but also increases plant community similarity (i.e., low β-diversity) at both scales. The effect of landscape structure showed differing trends depending on the habitat. In general, landscape composition of semi-natural land cover (i.e., hedgerows, watercourses) showed a positive effect on species diversity as opposed to that of the configuration of anthropogenic elements on both scales. Our results provided crucial information on the landscape processes useful to improving biodiversity conservation by EN. Our findings suggest that i) improving connectivity within ENs favors α plant diversity ii) different habitats have different sensibility to landscape structure iii) semi-natural land cover around nodes improve plant diversity; iv) planning both mono-habitat and multi-habitats nodes, increases the biodiversity conserved therein; v) nodes with more compact shapes are to be preferred.