Determinants for the conservation of a vulnerable fire-dependent species at its marginal range

We investigated the role of fire and other potential biotic and abiotic determinants for the occurrence of an obligate seeder and active pyrophyte, Cistus salviifolius, a vulnerable species in the Swiss Red List. Populations of this species are threatened by the change of fire regime that has occurred during the last ten years. Fires and burnt areas are today less frequent and it is not clear whether other factors can compensate for such fire-free periods should this trend continue. We used a stratified random design to collect data on the cover of three growth stages, i.e., juvenile, chamaephytic and nanophanerophytic (oldest), of C. salviifolius, on plant communities, and on environmental factors. A tree-based discriminant analysis showed that the time elapsed since last fire was the best predictor of Cistus occurrence, but plants could survive on rocky and sunny sites if no fire had occurred for more than 32 years. Contrary to our expectations, the number of fires and time elapsed since the last event was correlated with the oldest stages only, and not with that of seedlings or juveniles. Rank correlations showed that bare soil was a good predictor of young stages, whereas rocky outcrops and shallow soils were important for the chamaephytic stage. Our results confirm the role of disturbances and competition-free habitats as determinants of the survival of this vulnerable pyrophyte during long periods without fires and the existence of ontogenetic niche segregation of this species. In order to maintain viable C. salviifolius populations in the Alps, managers should undertake conservation actions according to the requirements of the different growth stages of this species.