The analysis of the influence of grazing intensity on the diversity and abundance of plants and spiders (Arachnida: Araneae)

Abstract

In restoration projects, low stock grazing has become a popular means of management. However, an accurate understanding of the effects of grazing on plants and spiders is often lacking. Although spiders and plants are not closely related evolutionarily or genetically, the relationship between them can be complex and diverse. Many species of spider build their webs or nests on plants, using the leaves, stems, or flowers as anchoring points. This provides them with protection from predators, access to prey and a stable habitat. On the other hand, spiders can provide a number of benefits to grassland ecosystems, such as helping to control populations of insects and other arthropods that can damage or consume grassland plants. This study addresses the effects of different grazing regimes on plant and spider diversity in siliceous grasslands. Plant and spider diversity was studied for four months in the Sharri Mountains (Kosovo) in order to determine the biodiversity in ungrazed, moderately grazed and overgrazed siliceuous grasslands. The responses of plant height, plant biomass, plant species diversity and spider species diversity to three grazing intensities at 12 sites were recorded. Vegetation structure (plant height and plant biomass) was significantly higher in ungrazed grasslands compared to grazed and overgrazed grasslands. This was not the case, however, for spider species richness and diversity, as these were higher in moderately grazed than ungrazed grassland. On overgrazed grasslands, spider diversity was extremely low, as only one species of spider (Pardosa saltuaria) was recorded. Plant and spider diversity increased in the following order: overgrazed grasslands < ungrazed grasslands < moderately grazed grasslands, in all the habitats studied. Different grazing intensities significantly affected the abundance of particular plants on siliceous grasslands, for example, Deschampsia cespitosa, one of the most dominant plants on siliceous grasslands had an abundance of 4.77% in ungrazed grasslands., but only 4.94% in moderately grazed grasslands and was absent in overgrazed grasslands. There were other species of plants that were most abundant in intensively grazed silicate grasslands. One of them was Nardus stricta, whose percentage in ungrazed, moderately grazed and overgrazed grasslands was characterized by a multiple exponential increase in % (s1 – ungrazed grasslands = 0.99%, s2 – moderately grazed grasslands = 1.25% and s3 – overgrazed grasslands = 10.50%). It is concluded that the intensity of grazing of natural grasslands directly affects biodiversity and that this information may be valuable for long-term management and conservation programs in similar habitats in SE Europe and beyond.