Connectivity and succession of open structures as a key to sustaining light-demanding biodiversity in deciduous forests

1. European forests are facing a rapid decline of light-demanding biota. This has prompted active interventions to re-establish and maintain partial habitat openness in protected areas. Managers of protected areas, however, need substantially more scientific evidence to support their decisions on where, when, and how to intervene.

2. We investigated the importance of spatial continuity of open forest habitats in different years of succession, using six pairs of experimental clearings established in the formerly open, oak-dominated forests of the Podyji National Park (Czech Republic). In each pair, one clearing was connected to the forest edge, while the other was isolated in closed forest. We sampled butterflies (74 spp.), moths (435 spp.), saproxylic beetles (465 spp.), and vascular plants (567 spp.) on the 12 clearings during the first five years of succession. We then compared species richness, abundance, and composition of the four taxa between the two clearing types and along the succession.

3. All studied insect groups were substantially more species-rich and more abundant in connected than in isolated clearings. Species composition of plants, moths, and butterflies differed between the clearing types.

4. The number of species of all studied taxa generally increased from the first to the second or third year after cutting; species composition of all taxa differed among years. This suggests rapid changes in habitat quality and thus limited time for colonisation by light-demanding organisms.

5. Synthesis and applications: Our results offer an evidence that spatial connectivity and rapid temporal dynamics are important habitat features for light-demanding insects. Attempts to create or restore habitats for light-demanding forest biota should take into account that: (i) Insects benefit from direct connection of new open patches to open habitats or flight corridors such as forest edges. (ii) Considering plants, the optimal solution is to connect newly created open forest habitats to existing habitats with established biota of high conservation value. (iii) Interventions should be carried out within short time intervals, i.e. within years rather than decades. (iv) A fine mosaic of interconnected, open woodland patches in various successional stages is more beneficial than a single large patch with a single successional stage.