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 'The distribution and impact of an invasive plant species (Senecio inaequidens) on a dune building engineer (Calamagrostis arenaria)' by Van De Walle et al., 2022, Neobiota (in progress).

The presence/absence data (PA) of Senecio inaequidens 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. The spatial parameters (proportion = P and Join counts = H) for all different scales (5, 10, 20 and 50m) are included as well as a combination of letter and scale (i.e. P_5 = proportion of marram grass cover in a 5m circle). 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 (='bkk', short for BezemKruisKruid, Dutch name for S. inaequidens) or not (=sand) and 'biota' represents whether biota could affect marram grass growth (biota = 0 thus means that the sand was sterilized). 'numb_leaves' = number of leaves, 'length_leaves_end' & 'length_roots_end' = length of the longest leave and root, 'leaves_fresh_end' & 'roots_fresh_end' = weight (in g) of the fresh leaves and roots, 'leaves_dry_end' & 'roots_dry_end' = dry weight (in g) of leaves and roots. All these measures were taken at the end of the experiment.

Abstract

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 (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. As marram grass plays a crucial role in natural dune formation, we evaluated the possible effects S. inaequidens could have on this process, if it would be able to naturalize 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, 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.