Unveiling the processes driving exotic plant invasion represent a central issue in taking decisions aimed at constraining the loss of biodiversity and related ecosystem services. The invasion success is often linked to anthropogenic land uses and warming due to climate change. We studied the responses of native versus casual and naturalised exotic species richness to land uses and climate at the landscape level, relying on a large floristic survey undertaken in North - Eastern Italy. Both climate and land use drove exotic species richness. Our results suggest that the success of plant invasion at this scale is mainly due to warm climatic conditions and the extent of urban and agricultural land, but with different effects on casual and naturalized exotic species. The occurrence of non-linear trends showed that a small percentage of extensive agricultural land in the landscape may concurrently reduce the number of exotic plant while sustaining native plant diversity. Plant invasion could be potentially limited by land management, mainly focusing on areas with extensive agricultural land use. A more consciousness land management is more and more commonly required by local administrations. According to our results, a shift of intensive to extensive agricultural land, by implementing green infrastructures, seems to be a win–win solution favouring native species while controlling the oversimplification of the flora due to plant invasion.
QuestionsUnderstanding the mechanisms underlying the impacts of exotic plant invasions is a central issue in plant ecology. Considering the invasion process, any alteration of the nutrient cycle is of fundamental importance. We hypothesized that the woody N‐fixing invasive Amorpha fruticosa is indirectly depleting plant diversity by altering ecosystem functions of riverine grasslands, thus producing a conspicuous shift in species composition.LocationTemperate lowland riparian areas of northeast Italy.MethodsIn 12 sites, we selected uninvaded, partially invaded, and invaded grasslands (36 plots). In each plot, we performed a vegetation relevé, measured main A. fruticosa growth traits, light transmittance and soil features. We studied the effects of the invasion of A. fruticosa on grassland properties and plant diversity, examining the interactions between soil nutrient cycles, light availability and plant diversity.ResultsIncreased abundance of A. fruticosa affected main soil properties (i.e. increase in soil mineralization and nitrification) and light availability (i.e. decrease in light). The δ15N of soil organic matter was strongly related to A. fruticosa basal area, thus supporting the hypothesis of an increase in soil nitrogen (N) availability due to invasion by the N‐fixer. Plant taxonomical and functional diversity decreased significantly as A. fruticosa cover increased. Plant diversity was more related with N than light availability or soil organic carbon. Similarly, the shift in species composition (i.e. beta diversity) of invaded grasslands was related to increased soil nitrification rates.ConclusionsOur findings show how a nitrogen‐fixing invasive plant such as A. fruticosa may influence the main ecosystem properties, causing cascading effects on soil functions, decreasing plant diversity. Alteration of the N cycle represents the key process involved in this plant invasion, suggesting that further studies should focus on potential solutions to mitigate the soil N supply, curb the invasion and restore plant diversity of these riverine grasslands.
Exotic plant invasions are considered one of the major threats to biodiversity causing important impacts at the population, community, and ecosystem levels. Understanding the drivers of plant invasions across multiple spatial and temporal scales often requires a landscape approach. The effect of landscape composition on biological invasion has been extensively studied, whereas landscape configuration effects were seldom considered or the analyses were limited to single species. Here, we aimed to analyze how the expansion of urban and agricultural areas can affect exotic species richness (both neophytes and archaeophytes) at three spatial scales, namely regional (scale: 37.5 km2), landscape (scale: 7.1 km2) and local (scale: 100 m2). We considered the possible contribution of urban and agricultural areas both in terms of composition (i.e. habitat cover) and configuration (i.e. shape complexity of patches). First, we found that increasing urbanization coupled with high shape complexity of urban elements were major drivers of both neophyte and archaeophyte invasions across heterogeneous landscapes. In particular, shape complexity seemed to be a key driver of plant invasions at large spatial scale, whereas the type of recipient habitat and urban cover determined the exotic success at the patch level. Second, archaeophytes were also affected by agriculture land use, i.e. agricultural patches shape complexity increased their spread at both regional and landscape scales. High shape complexity of highly disturbed habitats is expected to increase the exchange surface that exotic plant use to spread their propagules across the landscape mosaics. Our findings suggest that urban planning aimed at curbing urban fragmentation by both reducing shape complexity and diffuse urban sprawl might greatly improve the resistance of landscapes to biological invasions.
Identifying areas susceptible to invasion by an alien species is a strategy of prevention. We used national herbaria and global databases to assess the invasion trends of the two aquatic invasive species Ludwigia hexapetala and Ludwigia peploidessubsp. montevidensis in Italy. We defined the invasion status with invasions curves and predicted potentially suitable areas with Species Distribution Models based on WorldClim variables and the human footprint index. Low seasonal variation in temperature and precipitation, temperature ≥ 20 °C in the warmest, driest and wettest periods of the year and precipitation in the coldest period are the bioclimatic factors that most account for the potential distribution of the two species. The human footprint has lower relative importance than bioclimatic variables. All Italian peninsula appears as a suitable bioclimatic environment for the invasion of the two Ludwigia species, except the Alps and the highest peaks in the Apennine. Based on the current distribution of the species in Italy and the mostly densely invaded areas globally, the agricultural land surrounding the current invaded areas and along the Italian coasts is the most vulnerable to the invasion. Considering the trend of the invasion curves, which have been sharply rising for the latest decades, there are reasons to expect that the alien Ludwigia species will continue their expansion, if no timely and effective actions are taken. Informative campaigns, accurate monitoring and prompt management are fundamental preventive tools in areas predicted as vulnerable to invasion by this study.
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