Split-plot design of the growth experiment for the site at Oostduinkerke (Western Belgian coast). 2L samples of sand, (1) sand from unvegetated locations or (2) sand from underneath Senecio, were split into two 1L subsamples, one of which was sterilized. This enabled us to investigate whether the effect of Senecio was achieved via the biotic or abiotic portion of the soil. Map made with QGIS v3.6 (QGIS Development Team 2021). Aerial photograph (summer 2018) source: Agency for Information Flanders (geopunt.be).