Military training areas (MTAs) show high numbers of rare and threatened species and diverse habitat patterns due to low nitrogen input and heterogeneous disturbance dynamics caused by military training activities that produce fine-scale landscape mosaics. Since the 1990s, major parts of MTAs in Europe have been decommissioned. In Germany, most of them were transferred to the national natural heritage now facing the challenge of developing comprehensive conservation management strategies. In order to elucidate their current conservation value in terms of habitat patterns and associated breeding birds we selected 14 former MTAs (c. 200 km²). We defined semi-open landscapes as sparsely wooded (> 20−46% wood cover) to densely wooded (> 46−68%) transition zones between open land and forests. Out of 6,476 breeding bird territories in total, the guild of birds associated with semi-open landscapes was exceptionally large, accounting for 61% of the total and 71% of all threatened birds, while the total semi-open area made up only 28% of the study areas. Six selected keystone species (Anthus trivialis, Caprimulgus europaeus, Emberiza citronella, Lanius collurio, Lullula arborea, and Sylvia nisoria) depended on different species-specific key resources (optimal wood cover, single or combination of habitat types). We concluded that preserving/restoring such semi-open landscapes requires large-scale management approaches towards mosaics of different successional stages or structural elements with varying wood cover and associated habitat types, and should be adapted to the desired keystone species. Promoting combined open land/woodland management of semi-open landscapes should become a policy priority for adapting EU Common Agricultural Policy (CAP) to the needs of bird conservation.