Diachronic analysis of floristical changes on a suburban mediterranean archipelago (Frioul Islands, Marseille)

The insular systems are very vulnerable to various disturbances which can i nduce some important floristical changes. The aim of this study is to analy se the Bora changes which occurred within a 60 years period (between 1938 a nd 1997) on the two main islands, Pomegues and Ratonneau of the Frioul arch ipelago (Marseille, south-east France). We performed both a taxonomic and a functional analysis of the plant data. The function;il approach was made by the study of growth form, dispersal, G rime strategy, and biogeographical type of each plant species. We focused p articularly on the plant species newly established on the archipelago. The main results were: i) a prevalence of therophytic plant species within the newly established plants, ii) a constancy in the part made by each dispersa l mode, with a prevalence of taxa dispersed by wind, iii) an increase in th e part made by ruderal species, notably on Ratonneau island, iv) a slight d ecrease of mediterranean plant species on Ratonneau island. Changes which h ave occurred in the plant species seem to be due to several recent anthropo genic factors. These disturbances are particularly acute on Ratonneau islan d and are mainly the result of the building of 'Port Frioul' residential ar ea.