Ecological response to human trampling and conservation status of Helianthemum caput-felis (Cistaceae) at the eastern periphery of its range

Border and isolated plant populations represent an interesting target for ecological and conservation issues. We analysed the ecological constraints and the conservation status of the eastern population of Helianthemum caput-felis Boiss. (Cistaceae), located in Sardinia. The distribution of H. caput-felis was verified via field surveys; ecological data, morphological and reproductive traits, were recorded in 40 permanent plots randomly established; the human trampling effects on plant density, plant size and plant performance were analysed. Plant density was higher in bedrock and lowland areas, in garrigue and maquis habitats; however, the differences among plants growing in different ecological conditions were not statistically significant; only human trampling intensity significantly affected plant density and lowest values were observed in areas with intense trampling pressure. All ecological variables analysed had a statistically significant effect on plant size and on the number of fruits per plant. In particular, larger plants were found in areas with the following ecological features: presence of structured soil, on the slopes, in the maquis habitat, and in areas with intensive human trampling. Conversely, plants displayed a higher fruits output per plant in deep and structured soil, in lowland areas, and in the garrigue and maquis habitats; the mean fruits output per plant increased as human trampling intensified. Human-induced threats are the main hazards threatening the remaining Sardinian population. In particular, the major threats are linked to tourism and other outdoor activities (i.e. human trampling), followed by the expansion of agricultural activities; all of these threats result in the disappearance of small localities and in reduced population size due to habitat loss and fragmentation. Our study indicates that H. caput-felis should be considered as Critically Endangered (CR) at the regional level. Urgent measures should be undertaken to protect the remaining H. caput-felis population in Sardinia and a possible integrated strategy for the conservation and management consists of a combination of in situ and ex situ measures. In particular, greater emphasis should be given to minimizing the negative impacts of unsustainable tourism and recreation use, in order to exclude human trampling and to facilitate the plant recruitment process and population renewal. In addition, an ex situ conservation strategy must be implemented and the seeds collected could be used for future translocations in suitable areas. Moreover, considering the threats observed, a long-term monitoring programme must be developed to reveal changes in the species conservation status.