Fire recurrence effects on the structure and composition of Mediterranean Pinus halepensis communities in Catalonia (northeast Iberian Peninsula)

Does recurrence of fires affect the composition and structure of Mediterranean plant communities?The post-fire regeneration of communities dominated by Pinus halepensis was examined using a regional approach in Catalonia (northeast Iberian Peninsula). Twenty-eight study sites were selected. Each site consisted of two adjacent areas that differed in the number of fires that occurred during a period of two decades. One area burned only once, in 1994 (recurrence category 1, r1); the other area burned twice, once between 1975 and 1993 and again during the same 1994 fire (recurrence category 2, r2). Eight years after the 1994 fire, structural (height, cover, fuel model) and compositional (abundance of dominant species) data were collected, together with data on pine density and reproductive performance. The effects of fire recurrence, fire interval (FI), real solar radiation (RSR), land precipitation (PP) were analyzed. There was a structural simplification in twice-burned areas in comparison with once-burned ones. This simplification may result from changes in species composition and from differential growth potentials caused by effects of fire on soils. In addition, lower fuel loads occurred after two fires. Pinus halepensis populations declined and shrub abundance increased in twice-burned areas; an increase in grass abundance was not observed. Fire recurrence was the most relevant variable to explain differences in plant community characteristics. The importance of fire regime parameters in determining post-fire vegetation regeneration in Mediterranean-type ecosystems is underlined by this study.