What restricts generative rejuvenation of Calluna vulgaris in continental, dry heathland ecosystems: seed production, germination ability or safe site conditions?

A large-scale field experiment with different management options (free-range grazing, onetime cutting, additional disturbances and their interactions) was carried out in a continental, dry heathland. Within the framework of the experiment seed production and germination ability of over-aged Calluna individuals as well as specific safe site conditions were investigated to reveal restricting factors for the generative rejuvenation of Calluna. The calculated values of seed production and germination ability of over-aged Calluna individuals can be compared with those from literature or exceed the values reported there. Therefore, seed production and germination ability are not the limiting factors for the generative rejuvenation of Calluna. Free-range grazing with large herbivores combined with onetime cutting of over-aged Calluna stands supports the generative rejuvenation, especially due to the creation of specific safe sites, which are crucial for a successful survival of Calluna seedlings. Particularly a light shadowing seems to be the restricting factor for a successful generative rejuvenation of Calluna in continental, dry heathlands.