Diversity/dominance diagrams show that fire disrupts the evenness in Mediterranean pinewood forest bird assemblages

Breeding bird communities were studied by line-transect in burnt pinewood and unburnt pinewoods, during three years subsequently to a fire event, in a coastal woodland of Mediterranean central Italy. We analyzed data following a diversity/dominance approach that ranks the species in order of their abundance, to obtain rank/abundance diagrams ('Whittaker plots'). Although it is generally accepted that fire may induce structural changes in forest communities of breeding birds, we observed more evident effects when considering the assemblage of forest-specialist species. When considering the whole community of birds, ordinate intercepts of the regression between rank and relative abundance of species were not significantly different between unburnt and burnt plots in any of the three years of study. However, when considering only the forest-related species, there was a significant difference between unburnt and burnt plots in all the years of study. Evenness showed lower values that were explicited by the diversity/dominance diagrams (lower collocation of the curves of burnt pinewoods if compared to unburnt ones). Overall, the patterns observed in this study suggest that the effects of fire disturbance were more evident at the ecological level than at the taxonomic-level assemblages. The gradual decline of the more sensitive species due to fires and the proportional increase of edge/generalist species may induce a species turnover in burnt woods with cascade and relaxation effects which could be evidenced by diversity/dominance diagrams. Consequently, it is useful to separate the effects of fires at community-level and at assemblage-level when studying bird communities in areas subjected to fires.