Assessing the effects of Carpobrotus invasion on coastal dune soils. Does the nature of the invaded habitat matter?

We investigate the modifications of soil factors in Carpobrotus invaded sites by evaluating differences between non-invaded and highly invaded plots in three habitats of coastal dune ecosystems in Central Italy. Nitrogen content, organic matter content, pH and salinity were measured in three coastal habitats: shifting dunes along the shoreline with Ammophila arenaria, Crucianellion maritimae fixed beach dunes and fixed coastal dunes with Juniperus spp. Soil variables of the invaded plots were compared to non-invaded ones using two-way factorial ANOVAs and post-hoc Tukey HSD tests. We found significant differences between invaded and non-invaded plots for nitrogen content, organic matter content and pH in both foredune habitats. On the other hand, no differences were revealed on fixed dunes. Thus, we found distinct responses of soil factors to Carpobrotus invasion depending on the habitat. Pioneer habitats with very poor soils are more sensitive to invasion probably because the production of litter by Carpobrotus is considerably higher than for native species. Therefore, for the establishment of efficient alien control programs of those habitats of conservation interest, it is imperative to take into account the relationship between invasive species presence and the top soil characteristics. For instance, particular attention is required in the foredune zone (pioneer habitats), where Carpobrotus invasion is more likely to affect the parameters of the soil.