Stefania Pisanu

The conservation status of an endemic species of northern Sardinia: Centaurea horrida Badarò (Asteraceae).

Abstract When assessing the conservation status of narrow endemic plants, life history traits must be taken into account, since endemics combine small population ranges and sizes, and long persistence with limited reproductive and dispersal ability. In this paper, we present the global assessment of the conservation status of a narrow endemic plant from the Sardinian‐Corsican biogeographic province, by applying IUCN criteria and categories, together with an evaluation of some reproductive traits. Centaurea horrida Badarò (Asteraceae) is an endemic species of northern Sardinia (Italy). It is protected by the Bern Convention (Appendix I) and listed as priority species by the “Habitat” Directive (92/43/EEC, Annex II). The species appears in the 1997 IUCN Red List as “Vulnerable” (VU). With the aim of evaluating the risk of extinction and of providing management tools for the network of protected areas in which this species is present, some reproductive traits have been evaluated, and the distribution, size and structure of its population have been measured according to IUCN 2006 Guidelines. Centaurea horrida is not able to self‐pollinate and its effective seed dispersal ability is limited. Its extent of occurrence is 172.43 km2 and its area of occupancy is 108 km2. Population size has been estimated at 11,719 adult individuals. Significant differences in adult densities among sites have been highlighted. The structure of the population is dominated by adult individuals (on average 68%), while the proportion of seedlings is only 7% on average. Its habitat underwent an extinction rate of 18% in 50 years. On the basis of the data gathered, the status to be assigned to C. horrida is that of “Endangered” (EN). This first attempt to evaluate the conservation status of a narrow endemic plant from the Sardinian‐Corsican biogeographic province allowed us to conclude that the management of rare species must be site‐specific and that there is urgent need to acquire detailed data on endangered species, especially within biodiversity hotspots, and to continuously update Annex II of the EU Habitat Directive and the IUCN Red List.

A Natural Homoploid Hybrid between Centaurea horrida and Centaurea filiformis (Asteraceae) as Revealed by Morphological and Genetic Traits

Studies over the last two decades demonstrate that hybridization has played an integral role in the evolution of several sections of the genus Centaurea. Nevertheless, natural hybridization between narrow Mediterranean endemic Centaurea species has not been documented as yet. A population of fertile Centaurea individuals exhibiting intermediate morphological traits between two Sardinian narrow endemics, C. horrida and C. filiformis, was identified at the Tavolara Islet (Sardinia, Italy). Intermediate leaf length and head width characterized this population, suggesting its hybrid origin. The putative hybrid population was structured (i.e., composed of seedlings, saplings and adult individuals) and had a relatively high levels of seed production. The number of chromosomes was identical to that of the proposed progenitors (2n = 18). Genotyping at five microsatellite loci showed that the putative hybrid possessed several alleles in common with the proposed parental species and intermediate values of genetic differentiation, as indicated by both FST and RST, between C. horrida and C. filiformis. We therefore conclude that the studied intermediate population is of hybrid origin, and discuss possible mechanisms of its reproductive isolation from the parental species, potential re-introgression, and evolutionary implications of this hybridization.

Human trampling effects on Mediterranean coastal dune plants

Coastal habitats are particularly vulnerable to recreational impacts because these environments are highly dynamic and continually change in response to biotic and abiotic factors. Sand dune communities are worldwide characterized by high levels of biodiversity, but are often affected by human-induced impacts as those caused by tourist trampling. To understand the effects of human frequentation, trampling, and other human-induced impacts, fencing experiments have been traditionally carried out on coastal dunes. Since in touristic areas dune systems are subjected to different intensities of human frequentations rather than to opening or fencing, in this study we explore the effects of accessibility on vascular plants cover. This study tests the hypothesis that human frequentation on beaches affects spatio-temporal variability of vascular plant abundance on dunes by comparing the plant assemblages of high and low accessible sites in North-East Sardinia (Italy). Our results show that accessibility plays a crucial role in conditioning the percentage of vegetation cover in Mediterranean dunes. In fact, not only we found a perennial vegetation cover that was significantly higher in the sites with low accessibility (and consequently low frequentation), but we also showed that at the sites with high accessibility there were significant differences in vegetation cover between times of sampling (cover was higher before than after summer): on the contrary, differences in perennial vegetation cover among times were not significant at the low frequentation sites. After summer, the difference among low and high frequentation sites in species composition and cover was >90%. Multivariate analysis identified those species that play a pivotal role in differentiating the low and the high frequentation sites. Among them, Crucianella maritima and Sporobolus virginicus can be considered as differential species. Overall, our data show vegetation and plant species responses to human-induced impacts, and are therefore important to support conservation actions in Mediterranean coastal areas interested by mass tourism.

Variability at Local Scales and between Habitats in Population Structure and Reproductive Traits of the Mediterranean Plant Centaurea horrida: Implications for Management

Abstract Spatial variability in the structure of a population and in the reproductive traits of the narrow endemic coastal plant thorny knapweed (Centaurea horrida; Asteraceae) was estimated. Variations in the distribution of individuals and reproductive effort were described and quantified at the per-site scale (3 sites, less than 30 kilometers apart) for two habitats (cliff face and cliff plateau) to provide a basis for further investigations of the factors affecting C. horrida performance and to provide information necessary for an effective conservation of this species. Centaurea horrida was considerably more abundant at one site, especially in the cliff plateau, in the contribution of adults. Estimates of spatial variance for each life stage at both habitats revealed that, on the cliff plateau, a much greater variability was found at the per-site scale for classes of saplings and adults of middle size, whereas in the cliff face local (among replicates), spatial variance was higher for all comparisons. For all the reproductive traits considered, variation at the scale of the site in the two habitats was extremely low, whereas it was much more important among replicates, indicating that other determinants rather than recruitment are likely responsible for the heterogeneity in the abundance of adults across sites. Overall, these results suggested that, on cliff plateaus, different processes operate on the C. horrida population structure at the three sites. Consequently, site-specific management needs to be addressed. However, we believe that effective management strategies can only be proposed based on manipulative experiments that highlight the role of the major determinants of spatial patterns.

Thorn, spine and prickle patterns in the Italian flora

Abstract Spinescence refers to the presence of sharp appendages of various origins with ecological, evolutionary or biogeographic significance. This research was conducted to explore patterns and adaptive processes of thorns, spines and prickles in the Italian flora. We compiled an inventory of 401 spiny plants taking into account the following attributes: type of spinescence, family, biological form, chorotype, bioclimate and habitat. Then, we evaluated the incidence of plants with each attribute, the co-occurrence of various types of spinescence, the associations among spinescence types and biological forms and families, the structure of data across spinescence types, thermotypes and habitats. The spatial distributions and the adaptive processes of plants with various types of spinescence revealed that these patterns are driven by evolutionary, biogeographic and ecological factors, thus supporting the hypothesis that interactive processes of selective pressures and phylogenetic constraints have influenced the evolution of spinescences.