Successional Pathways of Avifauna in a Shifting Mosaic Landscape: Interplay between Land Abandonment and Wildfires

Abstract

In Mediterranean hinterlands, land abandonment has led to the encroachment of woody vegetation prone to fire. The resulting alternation between vegetation closure and sudden opening modifies the composition of avifauna. We first conducted a stratified sampling of the avifauna in a grassland-to-forest gradient representing the closure of vegetation after abandonment (space-for-time substitution). We then conducted postfire diachronic sampling (up to 42 years) on stations belonging to this gradient. Mid-successional shrubland avifauna was the most radically modified after fire—ground-nesting species replacing shrub-nesting species—without significant change in species numbers. In the medium term, shrub-nesting birds widened their distribution in the landscape. While avifauna postfire successions in shrubland paralleled the spontaneous colonization of grasslands by woody vegetation, postfire forest successions were distinguished by the persistence of certain forest birds, resulting in assemblages of high diversity in which open-habitat birds coexisted with forest species. This temporary vegetation–avifauna mismatch results from both the reluctance of open-habitat birds to enter burned areas because of numerous snags, and the site fidelity of breeding birds. This inertia mitigates the short-term impact of fire. In the long term, spontaneous or postfire successions converge towards a homogeneous forest avifauna, to the detriment of open-habitat species of high conservation value.