The distribution and impact of an invasive plant species (Senecio inaequidens) on a dune building engineer (Calamagrostis arenaria)

These data sets are used to run the analyses in the paper '<em>The distribution and impact of an invasive plant species (</em>Senecio inaequidens<em>) on a dune building engineer (</em>Calamagrostis arenaria<em>)</em>' by Van De Walle et al., 2022, Neobiota (in progress). The presence/absence data (PA) of <em>Senecio inaequidens</em> in European coastal dunes can be found in 'Senecio_PA.xlsx', in the tab 'senecio_PA', together with the country and location where the occurrences were mapped. All coordinates of the samples are available in the tab 'coordinates samples'. 'Marram_growth_experiment.xlsx' contains the data gathered during the growth experiment. The origin of the sand is subdivided in 3 columns: 'Location' represents the location along the Belgian coast where sand was gathered, 'senecio' represents whether sand was gathered from underneath a senecio plant or not and 'biota' represents whether biota could affect marram grass growth (biota = 0 thus means that the sand was sterilized). <strong>Abstract</strong> Disturbance is thought to enhance the probability of invasive species establishment, a prerequisite for naturalization. Coastal dunes are characterized 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 (<em>Senecio inaequidens</em>) in European coastal dunes. Local sand dynamics dictate the spatial configuration of marram grass (<em>Calamagrostis arenaria</em>). Therefore, marram grass configuration was used as a reliable proxy for disturbance. As marram grass plays a crucial role in natural dune formation, we evaluated the possible effects <em>S. inaequidens</em> could have on this process, if it would be able to naturalize in European coastal dunes. We expected the highest probability of <em>S. inaequidens </em>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 <em>S. inaequidens</em> is quite capable of handling higher levels of sand burial. Thus, probability of <em>S. inaequidens</em> 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 <em>Senecio</em>-altered soils on marram grass growth mediated by soil biota. However, marram grass grew better in sand gathered underneath <em>Senecio</em> plants due to abiotic soil modifications. This enhanced growth may be caused by <em>Senecio</em> leaf litter elevating nutrient concentrations in an otherwise nutrient-poor substrate. If such increased plant growth is a general phenomenon, further expansion of <em>S. inaequidens</em> could accelerate natural succession in European coastal dunes.