How do sheep affect plant communities and arthropod populations in temperate grasslands?

Abstract

Grasslands being used in sheep farming systems are managed under a variety of agricultural production, recreational and conservational objectives. Although sheep grazing is rarely considered the best method for delivering conservation objectives in seminatural temperate grasslands, the literature does not provide unequivocal evidence on the impact of sheep grazing on pasture biodiversity. Our aim was therefore to review evidence of the impacts of stocking rate, grazing period and soil fertility on plant communities and arthropod populations in both mesotrophic grasslands typical of agriculturally improved areas and in native plant communities. We therefore conducted a literature search of articles published up to the end of the year 2010 using 'sheep' and 'grazing' as keywords, together with variables describing grassland management, plant community structure or arthropod taxa. The filtering process led to the selection of 48 articles, with 42 included in the stocking rate dataset, 9 in the grazing period dataset and 10 in the soil fertility dataset. The meta-analysis did not reveal any significant trends for plant species richness or plant community evenness along a wide stocking rate gradient. However, we found frequent shifts in functional groups or plant species abundance that could be explained by the functional properties of the plants in the community. The meta-analysis confirmed that increasing soil fertility decreased plant species richness. Despite the very limited dataset, plant species richness was significantly greater in autumn-grazed pastures than in ungrazed areas, which suggests that choosing an appropriate grazing period would be a promising option for preserving biodiversity in sheep farming systems. Qualitative review indicated that low grazing intensity had positive effects on Orthoptera, Hemiptera (especially phytophagous Auchenorrhyncha) and, despite a diverse range of feeding strategies, for the species richness of Coleoptera. Lepidoptera, which were favoured by more abundant flowering plants, also benefited from low grazing intensities. Spider abundance and species richness were higher in ungrazed than in grazed pastures. In contrast, there are insufficient published studies to draw any firm conclusions on the benefits of late grazing or stopping fertilization on insect diversity, and no grounds for including any of this information in decision support tools at this stage.Keywords: biodiversity, grazing period, insect, stocking rate, soil fertility ImplicationsThere is a general trend toward a gradual intensification of ruminant production to meet the increasing demand for livestock products (Bouwman et al., 2005), which logically raises major concerns over the environmental consequences involved. Grassland intensification entails higher livestock densities and fertilizer application rates to increase soil productivity, which negatively affects the diversity of resident plant communities. Grasslands are being managed under a variety of agricultural production and conservation objectives;...

The response of spider (Araneae) assemblages to structural heterogeneity and prey abundance in sub-montane vegetation modified by conservation grazing

“…Auchenorrhyncha abundance markedly increased in relation to lower stocking densities during the experimental period, with the highest counts observed in the ''Mixed low'' treatment and ''Ungrazed'' control, consistent with the general relationship recorded for this Sub-Order in the literature up until 2010 (Scohier and Dumont, 2012). Taller average swards provide favourable microhabitats for Auchenorrhyncha, especially increased humidity, leaf surface area of host plants and microhabitats (Eyre, 2005).…”

Resource-Mediated Indirect Effects of Grassland Management on Arthropod Diversity

“…For instance, moderate grazing was found to have a positive effect on arthropod diversity in several studies [33] but we found only weak total effects of grazing intensity on arthropod diversity (<0.2). A wider range of grazing intensities in our study system compared to other studies might explain the absence of a positive effect in our case; e.g.…”

Land‐use type and intensity differentially filter traits in above‐ and below‐ground arthropod communities

“…These results are in line with previous studies that suggested that management effects on plant communities cascade up to reduce the dominance of herbivores in arthropod communities (Scherber et al . ; Scohier & Dumont ). Several traits, however, were not affected by land‐use intensity in our study, as for example the mobility trait in Carabidae and Oribatida, the feeding trait in Carabidae or the stratum trait in all taxa.…”