The value of old pine plantations in ants' conservation in the Mediterranean: a comparison with well-conserved forests

Restoring forests is a global priority action for reverting biodiversity loss and sustaining essential ecosystem services. Among the most widespread strategies, tree planting dominates efforts worldwide, but its capacity to recover biodiversity and ecosystem processes remains uncertain. In this context, ants are increasingly recognized as key indicators of ecological conditions due to their sensitivity to environmental change and their role in multiple ecosystem functions. In this study, we evaluated the ecological value of pine plantations by examining ant biodiversity and community composition in comparison with mature well-conserved reference forests in Mediterranean ecosystems. We specifically assessed how forest structure, soil properties, management practices and vegetation composition influence ant communities. Our results showed that mature forests host more forest-associated ant species, while plantations are dominated by widespread generalists. Structural heterogeneity and forest management favored forest species but reduced overall richness, abundance and Simpson diversity. In plantations, taller trees and older stands were associated with fewer widespread species, suggesting changes in the dominance structure of ant assemblages. Ant community composition was influenced by forest type, vegetation composition, and tree height. These findings indicate that pine plantations form different ant assemblages that do not fully replicate those of mature forests, even after a century. We highlight the importance of conserving existing native forests and the need to incorporate faunal metrics into success restoration assessments. • Ants are increasingly recognized as key indicators of ecological conditions. • Plantations supported different ant assemblages than mature reference forests. • Age since plantation did not favor recovery of forest-specialist ant diversity. • Conserving existing mature forests is essential for maintaining biodiversity.