Effects of continuous cover management on bird communities in a beech dominated forest region of Slovenia

Forest management can have a negative impact on the populations of some forest species. One solution has been to use management that is better at mimicking natural processes. However, the effectiveness of such systems for maintaining some taxa needs further research. We evaluated forest structure in European beech (Fagus sylvatica L.) dominated stands managed with uneven-aged, continuous cover silviculture, compared to an old-growth stand, and characterized their bird communities. The managed stands represented different developmental stages of the forest, including a mature stand (before regeneration cutting), a gap-cut stand (a mature stand in the process of partial cutting), and a young stand. The old-growth stand had many features distinguishing it from the managed stands. In the managed stands, tree diameter reached a maximum of 67 cm in the gap-cut stand, and the highest mean stand volume was 459 m³ ha^{- 1} in the mature stand. In the old-growth forest stand, the volume was 807 m³ ha^{- 1} and there were 24 trees ha^{- 1} larger than 67 cm in DBH. These large stems alone had a volume of more than 300 m³ ha^{- 1}. Additionally, the managed stands had a deadwood volume in the range of 19-25 m³ ha^{- 1}, mainly consisting of stumps and small diameter fragments, compared to 318 m³ ha^{- 1} in the old-growth forest. The number of bird species was linked to the number of niches available, resulting from the presence of large-diameter trees, a heterogeneous diameter at breast height structure, and varying densities in the lower forest layers, which was reflected in the density of breeding pairs, from 104 per 10 ha in the old-growth forest to 22-87 pairs per 10 ha in the managed stands. In the breeding season the Shannon index for the old-growth forest was 4.29 versus 2.81-3.94, in the young and gap-cut stand, respectively. Half of the species found in the old-growth forest nested in cavities. Rare, more specialized species occurred more often in the old-growth forest. The presence of a dynamic mosaic of forest development stages turned out to be important for the diversity of bird species. However, the presence of large old trees and deadwood are likely key factors for maintaining bird diversity. Thus, management practices should be modified to better focus on the protection of microhabitats supporting the species associated with them.