The importance of the Cisto-Lavanduletalia coastal habitat on population persistence of the narrow endemic Dianthus morisianus (Caryophyllaceae)

In Mediterranean coastal dune habitats, the facilitative mechanisms among plants could be crucial for the persistence of several plants for which survival is linked to a fragile equilibrium with the surrounding microenvironment. The aim of this study was to verify whether there exists a facilitative effect on Dianthus morisianus Vals., a narrow endemic plant of Sardinia, and to analyze the potential importance of facilitative effects via the analysis of the interaction outcome with the nurse plants. Forty-five plots of 1×1m were randomly placed within the habitat where D . morisianus grows preferentially, composed of sclerophyllous shrubs (Cisto-Lavanduletalia sensu Habitats Directive). All D . morisianus plants recorded within the plots were assigned to one of the three microhabitats identified: (i) open areas in the inter-shrub discontinuities, (ii) under shrubs canopy influence and (iii) inside the shrubs. For each D . morisianus plant, the reproductive or vegetative status and both morphological and reproductive traits, as well as the possible physical damage (grazing and trampling), were measured. Inside the Cisto-Lavanduletalia habitat there was a greater number of reproductive plants, whereas in the open patches the vegetative plants prevailed. Morphological and reproductive parameters varied significantly among microhabitats and showed higher values inside the shrubs. As expected, grazing and trampling negatively affected mainly plants growing in the open and below microhabitats. A strong facilitative interaction between D . morisianus and the coastal Cisto - Lavanduletalia habitat was found: this habitat had a crucial positive effect on the persistence of D . morisianus and preserved this threatened plant; therefore, it is essential to primarily conserve the Cisto-Lavanduletalia habitat.