Soil fertilisation contributes to mitigating forest fire hazard associated with Cistus monspeliensis L. (rock rose) shrublands

Abstract

Cistus monspeliensis shrublands are strongly exposed to fire hazard and are rapidly expanding on oligotrophic soils as a consequence of the abandonment of silvopastoral activities. We hypothesised that nitrogen (N) and phosphorus (P) fertilisation could contribute to reduce Cistus cover and biomass and to direct the regeneration of the vegetation from seed bank after fire to grasslands able to prevent recurrent wildfires. Two experiments were performed to evaluate the effects of NP fertilisation on plant assemblage composition, diversity, grazing value, dry matter production and Cistus shrubland regeneration in (i) established shrublands, or (ii) recovering vegetation in burned areas. In the shrublands, NP fertilisation negatively affected Cistus cover, regeneration and biomass and significantly improved grazing value without significant effect on plant diversity. In burned areas, NP fertilisation significantly suppressed C. monspeliensis seedlings, increased the grazing value during the first 3 years since the last fire while it significantly reduced plant diversity. The increased grazing value following fertilisation in both burned and unburned areas is high enough to support silvopastoral activities. Soil fertilisation can be a key tool to support the conversion of shrublands in oligotrophic soils into productive grasslands, particularly when surrounding forests and urbanised areas, to reduce wildfire hazards through pastoral activities.