Birgitta Svensson

Plants, insects and birds in semi-natural pastures in relation to local habitat and landscape factors

The preservation of remaining semi-natural grasslands in Europe has a high conservation priority. Previously, the effects of artificial fertilisation and grazing intensity on grassland animal and plant taxa have been extensively investigated. In contrast, little is known of the effects of tree and shrub cover within semi-natural grasslands and composition of habitats in the surrounding landscape on grassland taxa. We evaluated the effect that each of these factors has on species richness and community structure of vascular plants, butterflies, bumble bees, ground beetles, dung beetles and birds surveyed simultaneously in 31 semi-natural pastures in a farmland landscape in south-central Sweden. Partial correlation analyses showed that increasing proportion of the pasture area covered by shrubs and trees had a positive effect on species richness on most taxa. Furthermore, species richness of nectar seeking butterflies and bumble bees were negatively associated with grazing intensity as reflected by grass height. At the landscape level, species richness of all taxa decreased (butterflies and birds significantly so) with increasing proportion of urban elements in a 1-km2 landscape area centred on each pasture, while the number of plant and bird species were lower in landscapes with large proportion of arable fields. Our results differed markedly depending on whether the focus was on species richness or community structure. Canonical correspondence analyses (CCA) showed that the abundance of most taxa was ordered along a gradient describing tree cover within pastures and proportion of arable fields in the landscape. However, subsets of grassland birds and vascular plants, respectively, showed markedly different distribution patterns along axis one of the CCA. In contrast to current conservation policy of semi-natural pastures in Sweden, our results strongly advise against using a single-taxon approach (i.e., grassland vascular plants) to design management and conservation actions in semi-natural pastures. Careful consideration of conservation values linked to the tree and shrub layers in grasslands should always precede decisions to remove trees and shrubs on the grounds of promoting richness of vascular plants confined to semi-natural grasslands. Finally, the importance of landscape composition for mobile organisms such as birds entails that management activities should focus on the wider countryside and not exclusively on single pastures.

Habitat preferences of nest-seeking bumble bees (Hymenoptera: Apidae) in an agricultural landscape.

The aim of this study was to find out where bumble bee queens place their nests in the agricultural landscape. Nest-seeking behaviour was used to indicate nesting site preferences. Four types of agricultural landscape were investigated near Uppsala, Sweden: open, relatively open, relatively wooded and wooded. Twelve 500-metre-long transects, each including several intermingled habitats (e.g., field boundaries, pastures, clearings), were inspected repeatedly over a two-month period, from April to June 1991. In total, 147 observations of bumble bee queens (Bombus spp.) of eight species were recorded. Nest-seeking queens were observed most frequently along forest boundaries and field boundaries, in open uncultivated areas and in the relatively open landscape, whereas they were least frequent in forest and in clearings. Fields, pastures and road boundaries had intermediate frequencies. Differences among species were found in terms of both landscape type and habitat preferences: B. terrestris, B. lapidarius, B. sylvarum and B. subterranius preferred open terrain, whereas B. lucorum and B. pascuorum preferred forest boundaries. Withered grass and tussocks were the preferred nest-seeking patches among all species.