Dispersal of open habitat and woodland plant species using semi-open landscapes as stepping stones

Biodiversity loss has advanced at an alarming rate in recent years. Man-made habitat fragmentation is one of the major reasons for plant diversity loss. The increase of changing land use and infrastructure expansion impedes the genetic exchange between populations and drives the loss of genetic diversity resulting in population losses and species extinction. On top, habitat fragmentation potentiates the effects of climate change, by hindering much needed species migration and adaptation to shifts in phenology or species range. To counteract the adverse effects of habitat fragmentation, linear dispersal corridors were introduced to connect same-type habitats with each other and enhance species dispersal between these habitats. In an exhaustive literature review, this thesis has dealt with the benefits and shortcomings of linear dispersal corridors for plant dispersal and has shown that the results for successful plant dispersal are mixed and that linear dispersal corridors are not always a perfect solution. This thesis then focusses on the possibility of linear dispersal corridors (e.g. woodlands) forming a barrier for other habitat types (e.g. open habitats) and with that, becoming an obstruction for plant dispersal (e.g. open habitat species). Looking for alternative solutions for plant dispersal, this thesis concentrates on European pasture landscapes, which have been managed by livestock grazing over centuries and today, are made up by a mosaic of open habitat patches, single trees and tree groups and feature a high phytodiversity. The high structural diversity of these semi-open pasture landscapes offers a variety of environmental conditions and therefore, these semi-open pasture landscapes are able accommodate species with various habitat requirements. Taking the structural diversity of these so-called “semi-open habitats” into account, they may be able to simultaneously connect patches of both open habitats and woodlands and serve as a “semi-open corridor” promoting species dispersal of both habitat types. However, due to plants’ sessile character and thus limited dispersal power, plants’ diaspores may not be able to disperse through the full extent of a corridor during a single dispersal event. The seeds may have to recruit seedlings and reproduce after establishment, so that a new seed can disperse further. In this case, semi-open corridors act as stepping stones and therefore, the complete plant life cycle must be taken into consideration when researching plant dispersal into semi-open habitats. Thus, an observational study surveying the occurrence of open habitat and woodland plant species in semi-open habitats and an experimental setup with open habitat and woodland plant species sown into semi-open habitats investigating their recruitment ability in two different geographical settings in Germany form the basis of this thesis.