Abstract
Disturbance is thought to enhance the probability of invasive species establishment, a prerequisite for naturalisation. Coastal dunes are characterised by disturbance in the form of sand dynamics. We studied the effect of this disturbance on the establishment and spread of an invasive plant species (Senecio inaequidens) in European coastal dunes. Local sand dynamics dictate the spatial configuration of marram grass (Calamagrostis arenaria). Therefore, marram grass configuration was used as a reliable proxy for disturbance. Since marram grass plays a crucial role in natural dune formation, we evaluated the possible effects S. inaequidens could have on this process, if it is able to naturalise in European coastal dunes. We expected the highest probability of S. inaequidens establishment at intermediate marram grass cover because too low cover would increase sand burial, whereas high cover would increase competition. However, our results indicate that S. inaequidens is quite capable of handling higher levels of sand burial. Thus, the probability of S. inaequidens establishment was high under low marram cover but slightly lowered when marram cover was high, hinting at the importance of competition. We expected a negative impact of Senecio-altered soils on marram grass growth mediated by soil biota. However, marram grass grew better in sand gathered underneath Senecio plants due to abiotic soil modifications. This enhanced growth may be caused by Senecio leaf litter elevating nutrient concentrations in an otherwise nutrient-poor substrate. If such increased plant growth is a general phenomenon, further expansion of S. inaequidens could accelerate natural succession in European coastal dunes.
Highlights
Due to human activity the number of invasive species worldwide is ever-increasing
Since marram grass plays a crucial role in natural dune formation, we evaluated the possible effects S. inaequidens could have on this process, if it is able to naturalise in European coastal dunes
The four models selected were all at the 5 m scale, implying that S. inaequidens reacts to marram grass spatial configuration at small distances
Summary
Due to human activity the number of invasive species worldwide is ever-increasing. In Europe alone, the number was estimated to be well over 12 000 in 2019 (Roy et al 2019). After reaching a new habitat, the non-native species needs to establish and naturalize in order to become invasive (Richardson et al 2000). It is generally thought that disturbance benefits establishment of non-native species and that it could even facilitate the spread of invasive species. Several mechanisms, such as reduced competition, increased resource input and increased habitat availability, are proposed to be behind this phenomenon (Mack et al 2000; Pyšek and Richardson 2006; Jauni et al 2015; Lear et al 2020)
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