Bird response to woody pastoral management of ancient chestnut orchards: A case study from the southern Alps

Wood-pasture abandonment is an important cause of structural homogenisation in traditionally managed forest landscapes across the Alps. In the present study, bird response to the restoration of ancient abandoned chestnut orchards was investigated by a pairwise-comparison of species richness and community composition in 94 managed and unmanaged chestnut orchards on the southern slope of the Swiss Alps. Sixty-one bird species were tracked during four breeding seasons. Although managed orchards were more environmentally heterogeneous, the average number of bird species was only slightly higher in managed than unmanaged orchards, and no differences were found in species abundance and composition. We found, instead, five times as many bird species associated with managed chestnut orchards (i.e., five indicator species and 10 species exclusively observed in managed orchards) as compared to unmanaged orchards that only had one indicator and two exclusive species. We also found 11 species to be significantly associated with managed orchards that have higher bird species richness and are mainly characterized by low tree coverage (< 62.5%). We hypothesise that these results are mainly due to: (i) the high mobility of birds and the small patch size of managed orchards which may have mitigated the stronger effects expected on bird communities, and (ii) the naturally small populations of those bird species favoured by restoration which were masked by the most frequent and dominant species. Moreover, the resilience of bird communities to restoration could also be due to the long history of forest management and wildfires south of the Alps. When planning chestnut orchard restoration and management, we recommend considering a tree cover threshold of below 62.5% as a measure that promotes high bird species richness.