Understanding the influence of urbanization on invasibility: Carpobrotus edulis as an exemplar

Driving effects of land use and landscape pattern on different spontaneous plant life forms along urban river corridors in a fast-growing city

River corridors are critical in connecting fragmented greenspace and providing habitats for plants and animals. There is a paucity of information on the detailed influence of land use and landscape patterns on the richness and diversity of distinct life forms of urban spontaneous vegetation. This study aimed to identify the variables that dramatically affect spontaneous plants and then disentangle how to manage such a variety of land types to maximize the biodiversity-supporting function of urban river corridors. The total species richness was remarkably influenced by the amount of commercial, industrial, and waterbody area and the landscape complexity of water, green space, and unused land. In addition, the spontaneous plant assemblages of different life forms significantly differed in their responses to land use and landscape variables. Vines were more sensitive to urban sites, i.e., strongly negatively affected by residential and commercial areas but positively supported by green space and cropland. Multivariate regression trees indicated that the total plant assemblages were clustered most remarkably by the total industrial area, and the classified responding variables differed among distinct life forms. The colonizing habitat of spontaneous plants explained a high proportion of the variance and was also closely related to the surrounding land use and landscape pattern. These scale-specific interaction effects ultimately determined the variation in richness among various spontaneous plant assemblages in urban sites. Based on these results, in future city river planning and design, spontaneous vegetation could be protected and promoted by a nature-based solution according to their adaptability and preference for distinct landscape characteristics and habitat features.

Human-derived effects and failure in management drive coastal urban foredune degradation and novel vegetation structure

Urbanization can drive significant decay in species diversity and abundance; in dune ecosystems the composition changes at a pace with changes in spatial fragmentation. Infrastructure deployment and human activities may provoke synergistically a reduction in dune patch size and/or habitat loss and thus a potential for rapid establishment of exotic species, producing a 'novel' habitat configuration. In this study we examine the effects of coastal urbanization and associated human activities in foredune patch fragmentation and changes in floristic composition and abundance in an urban-rural gradient. Using samples from a recently bulldozed and managed urban foredune area, we assess the legacy of erroneous practices associated with planting of exotic species in urban settings. We found a significant increase in foredune fragmentation, estimated as the occurrence of marks left by vehicles (4WD, 2WD) and people in foredunes close to or within urban settings. A marked change from native to non-native plant species was found from rural to urban environments, with non-native species contributing to increase species richness in urban settings. A positive relationship of non-native species with level of foredunes fragmentation was found. Dominance of non-native species was persistent through time in altered foredune patches. Our findings showed that incorporation of non-native species for aesthetic or engineering purposes in bulldozed foredunes, could limit colonization of native species through rapid establishment and complete dominance of non-native ones. Historical activities associated with coastal infrastructure upgrades seem to configure the present foredune floristic pattern present in urbanized coasts. Management strategies correcting past erroneous actions and promoting foredune rehabilitation could help the conservation of services that these 'novel' habitats provide in coastal urban environments.

Geographic patterns of seed trait variation in an invasive species: how much can close populations differ?

Seeds play a major role in plant species persistence and expansion, and therefore they are essential when modeling species dynamics. However, homogeneity in seed traits is generally assumed, underestimating intraspecific trait variability across the geographic space, which might bias species success models. The aim of this study was to evaluate the existence and consequences of interpopulation variability in seed traits of the invasive species Carpobrotus edulis at different geographical scales. We measured seed production, morphology, vigour and longevity of nine populations of C. edulis along the Catalan coast (NE Spain) from three differentiated zones with a human presence gradient. Geographic distances between populations were contrasted against individual and multivariate trait distances to explore trait variation along the territory, evaluating the role of bioclimatic variables and human density of the different zones. The analysis revealed high interpopulation variability that was not explained by geographic distance, as regardless of the little distance between some populations (< 0.5 km), significant differences were found in several seed traits. Seed production, germination, and persistence traits showed the strongest spatial variability up to 6000% of percent trait variability between populations, leading to differentiated C. edulis soil seed bank dynamics at small distances, which may demand differentiated strategies for a cost-effective species management. Seed trait variability was influenced by human density but also bioclimatic conditions, suggesting a potential impact of increased anthropogenic pressure and climate shifts. Geographic interpopulation trait variation should be included in ecological models and will be important for assessing species responses to environmental heterogeneity and change.

Conservation of a Critically Endangered Endemic Halophyte of West Portugal: A Microcosm Assay to Assess the Potential of Soil Technology for Species Reintroduction

The soil system has been frequently overlooked during plant reintroduction planning and practice since working with soils and plant roots can be difficult, particularly in saline environments. Coastal saline environments are major contributors to regional and global biodiversity and an important source of endemic species. However, various species are in decline or considered threatened, particularly halophytes (salt tolerant) due to negative anthropic impacts. The Lusitanian endemic halophyte Limonium daveaui formerly had a large distribution range along the west coast of Portugal but currently it shows a restricted distribution in the Tagus estuary. Field surveys revealed that this critically endangered species forms few local populations with small size invaded by exotic species. In this study, we investigated the potential utilization of Technosols, an innovative sustainable, ecological engineering method combined with brackish water irrigation for potential L. daveaui reintroduction in native habitats. Seed germination percentages were evaluated in different environmental conditions. Through a microcosm assay, a Technosol was constructed using a saline Fluvisol with a mixture of low value inorganic and organic wastes, which were chemically characterized. Plants were cultivated in the Fluvisol and Technosol and irrigated with brackish water collected in the nearby area. To assess plant growth, morphometric parameters and the plants’ physiological status were assessed and the fresh and dry biomass determined. Results showed that seed germination was higher on moist filter paper with distilled water than in Fluvisol or Technosol. Plants grown in Technosol had a greater development, with higher values of photosynthetic indexes and biomass production than in Fluvisol. Our findings provide a basis for future in situ conservation studies and support the idea that eco-friendly soil technology approaches are beneficial to conserve rare halophyte species.

Urbanization and Carpobrotus edulis invasion alter the diversity and composition of soil bacterial communities in coastal areas

Coastal dunes are ecosystems of high conservation value that are strongly impacted by human disturbances and biological invasions in many parts of the world. Here, we assessed how urbanization and Carpobrotus edulis invasion affect soil bacterial communities on the north-western coast of Spain, by comparing the diversity, structure and composition of soil bacterial communities in invaded and uninvaded soils from urban and natural coastal dune areas. Our results suggest that coastal dune bacterial communities contain large numbers of rare taxa, mainly belonging to the phyla Actinobacteria and Proteobacteria. We found that the presence of the invasive C. edulis increased the diversity of soil bacteria and changed community composition, while urbanization only influenced bacterial community composition. Furthermore, the effects of invasion on community composition were conditional on urbanization. These results were contrary to predictions, as both C. edulis invasion and urbanization have been shown to affect soil abiotic conditions of the studied coastal dunes in a similar manner, and therefore were expected to have similar effects on soil bacterial communities. Our results suggest that other factors (e.g. pollution) might be influencing the impact of urbanization on soil bacterial communities, preventing an increase in the diversity of soil bacteria in urban areas.

Drifting away. Seawater survival and stochastic transport of the invasive Carpobrotus edulis

Coastal areas are vulnerable and fluctuating habitats that include highly valuable spaces for habitat and species conservation and, at the same time, they are among the most invaded ecosystems worldwide. Occupying large areas within Mediterranean-climate coastlines, the "ecosystem engineer" Carpobrotus edulis appears as a menace for coastal biodiversity and ecosystem services. By combining the observation, current distribution, glasshouse experiment, and dispersion modeling, we aim to achieve a better understanding of the successful invasion process and potential dispersion patterns of C. edulis. We analyzed the response of plant propagules (seeds and plant fragments) to seawater immersion during increasing periods of time (up to 144 h). After 2 months of growth, plant fragments showed a total survival rate (100%) indicating high tolerance to salinity. During this time, fragment length was increased (up to 60%) and root length was higher than control in all cases. Also, immersed fragments consistently accumulated more biomass than control fragments. After two months of growth, photosynthetic parameters (F_v'/F_m', Φ_NO, and Φ_II) remained stable compared to control fragments. Physiologically, osmolyte and pigment content did not evidence significant changes regardless of immersion time. Based on the capacity of propagules to survive seawater immersion, we modeled the potential transport of C. edulis by combining an oceanic model (ROMS-AGRIF) with a particle-tracking model. Results indicated that propagules may travel variable distances maintaining physiological viability. Our model suggested that short-scale circulation would be the dominant process, however, long-scale circulation of propagules may be successfully accomplished in <6 days. Furthermore, under optimal conditions (southerly winds dominance), propagules may even travel large distances (250 km alongshore). Modeling transport processes, in combination with the dynamics of introduction and expansion, will contribute to a better understanding of the invasive mechanisms of C. edulis and, consequently, to design preventive strategies to reduce the impact of plant invasion.

Effect of human activities on floristic composition and diversity of desert and urban vegetation in a new urbanized desert ecosystem

Human impact in newly urbanized deserts creates new environments that may favor the establishment/dominance of certain plant species. In this study, we showed how the human activities during desert urbanization do affect distribution, composition and diversity of plant species in a new urban ecosystem. In a field study during 2015–2016 and 2017–2018 growing seasons, we investigated these vegetation criteria in three new habitats created recently due to human manipulations in addition to the old habitat of such area (i.e. the desert). We also compared vegetation criteria comprising the floristic cover, composition and diversity between the desert locations inside and on the outskirts of the city. The detrended correspondence analysis (DCA) successfully separated the different habitats studied. Besides, the floristic composition and diversity were significantly varied amongst these habitats. The canonical correspondence analysis (CCA) revealed an apparent correlation between floristic composition and soil criteria across the study area. For the desert vegetation, the cover values of both Tamarix nilotica and Zygophyllum coccineum, in addition to the whole diversity indices, were significantly suppressed in the desert fragments inside the newly constructed city in comparison with their cover in the desert adjacent to it. Moreover, the cover of both species was significantly declined in 2018 compared with their cover in 2015. On converse, the covering areas of Phragmites australis and Bassia indica were increased after intensive constructions in 2018. These results suggest that the human activities and, consequently, urbanization may influence plant life in newly urbanized desert ecosystems, leading to dispersal of new species and destruction of plant cover in some parts of the desert. Efforts and conservation strategies should be devoted to save the desert species that are vulnerable to elimination due to expansion of urbanization.