Lack of regeneration and climatic vulnerability to fire of Scots pine may induce vegetation shifts at the southern edge of its distribution

Aim Forest ecosystems dominated by fire-sensitive species could suffer shifts in composition under altered crown fire regimes mediated by climate change. The aims of this study were to: (1) study the spatio-temporal patterns and the climatic distribution of fires in Scots pine (Pinus sylvestris) forests during the last 31 years in north-eastern Spain, (2) evaluate the climatic vulnerability to fire of these forests in Spain, (3) analyse the regeneration of Scots pine after fire, and (4) predict the mid-term maintenance or replacement of Scots pine in burned areas. Location Catalonia (north-eastern Spain): the southern distribution limit of Scots pine. Methods We characterized the spatio-temporal and the climatic distribution of fires that occurred in Catalonia between 1979 and 2009. We used a generalized linear model to characterize the climatic vulnerability to fire of Scots pine in the whole of Spain. We assessed the regeneration of the species after crown fires in nine burned areas in Catalonia. The resulting data were integrated into a stochastic matrix model to predict the mid-term maintenance or replacement of Scots pine in burned areas. Results During the last three decades, Scots pine forests distributed in dry sites were most affected by fire. Our assessment of the vulnerability to fire of Scots pine forests in Spain as a whole, based on climatic and topographical variables, showed that 32% of these forests are vulnerable to fire, and that this proportion could increase to 66% under a conservative climate change scenario. Field data showed almost no regeneration of Scots pine after crown fires, and a limited capacity to recolonize from unburned edges, even in relatively old fires, with 90% of recruits located in the first 25 m from the edge. This process could be delayed by the elapsed time for new recruits to achieve reproductive maturity, which we estimated to be c. 15 years. Finally, our matrix model predicted the replacement of burned Scots pine forests by oak (Quercus sp.) forests, shrublands or mixed resprouter forests. Main conclusions Increased vulnerability to fire of Scots pine forests under future, warmer conditions may result in vegetation shifts at the southern edge of the distribution of the species.