Using evolutionary grazing histories to develop proactive conservation strategies for grassland systems.

How do large herbivores affect grassland communities with regard to their evolutionary grazing histories? And how can we use this knowledge to develop conservation strategies for these areas? This bachelor thesis aims to provide an answer to these questions by constructing an overview of the effects of grazing to a grassland system (with either a short or a long evolutionary history of grazing) in the absence or presence of large herbivores. Grazing is defined as a gradient from low to high grazing intensity (i.e. grazing can be “low”, “intermediate” or “high”). To construct this overview, first and foremost the generalized grazing model for grasslands created by Milchunas et al. (1988) is used. In addition, the intermediate disturbance hypothesis is used to clarify differences in magnitude of disturbance caused by grazing to different communities. Furthermore, it is considered how plant-plant interactions are altered in the presence of increasing grazing pressure by large herbivores. Grassland communities with a short evolutionary history are less resistant to stress induced by grazing than communities with a long evolutionary history. From a conservation point of view, low stocking rates are optimal for communities with a short evolutionary grazing history and intermediate stocking rates are optimal for communities with a long evolutionary grazing history. High stocking rates of large herbivores should always be avoided in grassland communities with a short evolutionary history of grazing, or else the system will become susceptible to invasion by exotic species and ultimately degrade. Abandoning grazing entirely results in a homogeneous vegetation structure dominated by a few plant species that outcompete all others, resulting in diminished habitat opportunities and diversity in higher trophic groups.