Examining the temporal effects of wildfires on forest birds: Should I stay or should I go?

Abstract

In flammable ecosystems, forest dynamics are affected by fire suppression, climate change and changes in land use that cause the frequency and intensity of fires to diverge from natural fire regimes. Although afforestation provides new habitats for forest species, fire can reverse its benefits by penalizing forest species. Shorter fire recurrence may also affect the capacity of original habitats to recover with post-fire salvage logging adding to the picture and having both direct and indirect effects on birds. To identify the underlying factors driving temporal variations in forest bird populations after wildfires, we performed counts in 685 transects located in 68 burnt areas in Catalonia (NE Iberian Peninsula), ranging from one to 11 years post-fire. Among the 20 studied forest species, 18 related significantly to time since fire and 14 to water deficit. Post-fire bird responses mainly fitted to non-lineal responses, such as irruptive and inverse-irruptive trends; whereas water deficit matched with the inclined and bell-shaped trends. Individual site fidelity seems behind the decision of forest birds to stay or leave after a fire, leading to increase frequency of occurrence immediately after fire but this effect tends to diminish over time. In terms of the spatial characteristics of burnt areas, the majority of species showed a positive relationship with fire severity heterogeneity and the density of unburnt patches. On the other hand, salvage logging negatively affected forest bird diversity. Bird diversity also decreased with the time since fire and in the driest transects but fire heterogeneity was positive for alpha and beta bird forest diversity. The relationships between forest birds and the mosaic of burnt and unburnt areas created by wildfires plays a critical role in maintaining biodiversity in fire-prone ecosystems. Thus, limiting post-fire disturbance (e.g. salvage logging) and promoting natural regeneration could be an effective strategy that will benefit forest organisms such as birds. Maintaining unburnt patches and creating a mosaic of burn severity and vegetation will promote habitat heterogeneity and benefit a diverse range of bird species.