Key structural attributes of Mediterranean reforestations for avian diversity conservation: comparisons with mature forests

Reforestation is a widely promoted strategy to restore Mediterranean forests. However, its effectiveness in recovering avian diversity (key for ecosystem processes such as seed dispersal and insect control) remains unclear. We studied bird communities in 28 reforestations and 25 mature forests in central Spain, assessing bird species richness, community composition, and functional guild proportions. Bird communities were surveyed using passive acoustic monitoring, and forest structure was characterized by measurements of tree diameter, height, density, canopy and shrub cover, and deadwood volume. Mature forests hosted on average 10.5 % more species and higher proportions of cavity-nesters, insectivores, and long-distance migrants than reforestations. Structural differences, particularly larger mean tree size (+8.8 %) and lower tree density (-6.6 %), explained part of these richness patterns, while deadwood volume and canopy cover were linked to community composition and the prevalence of specialist guilds. Although reforestations supported fewer species, they already host a substantial part of the regional avifauna and show potential for further recovery as structural characteristics typical of mature forests. These findings highlight that reforestation can meaningfully contribute to bird conservation in Mediterranean landscapes, but its ecological value depends on promoting structural complexity. Conservation strategies should combine structural maturity recovery in reforestations, while safeguarding remnant mature forests, which remain irreplaceable for supporting diverse and functionally important bird guilds.