Proforestation is increasingly recognized as an effective strategy for enhancing biodiversity, particularly through the promotion of structural complexity and habitat heterogeneity. In this study, we investigated the effects of forest management abandonment on bird communities in a Mediterranean forest in Croatia. We compared three forest stands representing stages of proforestation: one actively managed, one abandoned for over 30 years, and one abandoned for more than 60 years. Forest structure was also surveyed in each stand to assess habitat complexity and support interpretation of bird community patterns.
Bird data were collected using bioacoustic audio recorders (AudioMoths), which recorded 30-second audio samples every 10 minutes throughout the day from April to June 2025. Recordings were analysed with BirdNET, an automated bird sound recognition tool. Detections were filtered by applying a confidence threshold (>0.3) and excluding: (i) species detected fewer than 20 times across all sites; (ii) species ecologically incompatible with the study area (e.g., aquatic, alpine, or wintering species); and (iii) overflying species unlikely to use forest habitats, such as buzzards, and swifts. High-confidence detections were subsequently reviewed by an expert to minimise false positives.
Results revealed a significant positive effect of long-term abandonment on avian vocal activity, used as a proxy for bird abundance. In contrast, species richness did not differ among the stands. These findings suggest that while species composition remains relatively stable, differences in structural complexity - particularly in long-abandoned stands - can influence bird abundance patterns, with higher vocal activity associated with more complex habitats.
These findings support the role of proforestation in enhancing bird abundance in Mediterranean forests, even when species richness remains unchanged. Furthermore, the use of passive acoustic monitoring, when paired with rigorous filtering and expert validation protocols, represents an effective and scalable approach for assessing biodiversity responses to forest management practices.