Bo Söderström

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.

ESTIMATING SPECIES RICHNESS AND ACCUMULATION BY MODELING SPECIES OCCURRENCE AND DETECTABILITY

A statistical model is developed for estimating species richness and accumulation by formulating these community-level attributes as functions of model-based estimators of species occurrence while accounting for imperfect detection of individual species. The model requires a sampling protocol wherein repeated observations are made at a collection of sample locations selected to be representative of the community. This temporal replication provides the data needed to resolve the ambiguity between species absence and nondetection when species are unobserved at sample locations. Estimates of species richness and accumulation are computed for two communities, an avian community and a butterfly community. Our model-based estimates suggest that detection failures in many bird species were attributed to low rates of occurrence, as opposed to simply low rates of detection. We estimate that the avian community contains a substantial number of uncommon species and that species richness greatly exceeds the number of species actually observed in the sample. In fact, predictions of species accumulation suggest that even doubling the number of sample locations would not have revealed all of the species in the community. In contrast, our analysis of the butterfly community suggests that many species are relatively common and that the estimated richness of species in the community is nearly equal to the number of species actually detected in the sample. Our predictions of species accumulation suggest that the number of sample locations actually used in the butterfly survey could have been cut in half and the asymptotic richness of species still would have been attained. Our approach of developing occurrence-based summaries of communities while allowing for imperfect detection of species is broadly applicable and should prove useful in the design and analysis of surveys of biodiversity.

Different nest predator faunas and nest predation risk on ground and shrub nests at forest ecotones: an experiment and a review

Abstract This study examined predator faunas of artificial ground and shrub nests and whether nest predation risk was influenced by nest site, proximity to forest edge, and habitat structure in 38 grassland plots in south-central Sweden. There was a clear separation of predator faunas between shrub and ground nests as identified from marks in plasticine eggs. Corvids accounted for almost all predation on shrub nests whereas mammals mainly depredated ground nests. Nest predation risk was significantly greater for shrub than for ground nests at all distances (i.e. 0, 15 and 30 m) from the forest edge. However, nest predation risk was not significantly related to distance to forest edge, but significantly increased with decreasing distance to the nearest tree. Different corvid species robbed nests at different distances from the forest edge, with jays robbing nests closest to edges. We conclude that the relationship between the predation risk of grassland bird nests and distance to the forest edge mainly depends on the relative importance of different nest predator species and on the structure of the forest edge zone. A review of published articles on artificial shrub and ground nest predation in the temperate zone corroborated the results of our own study, namely that shrub nests experienced higher rates of depredation in open habitats close to the forest edge and that avian predators predominantly robbed shrub nests. Furthermore, the review results showed that predation rates on nests in general are highest <50 m inside the forest and lower in open as well as forest interior habitats (≥50 m from the edge).

The effects of management regimes and location in landscape on the conservation of farmland birds breeding in semi-natural pastures

Abstract Semi-natural dry grasslands have almost disappeared in the modern farmland of southwestern and central Europe. In the northern and eastern parts of Europe, however, this species-rich habitat is still relatively common, albeit in a phase of rapid loss. To halt this decline the Swedish government started a large-scale subsidy scheme for the management and restoration of semi-natural pastures mainly aimed at increasing botanical values. We compared and contrasted the current management prescriptions with habitat preferences of 23 farmland bird species breeding in 88 dry semi-natural pastures in south-central Sweden. Semi-natural pastures showed very high breeding densities of several farmland birds underlining the importance of this habitat to the conservation of farmland birds. A TWINSPAN classification of all birds identified two groups of pastures with different bird communities. Eleven (48%) of the bird species were significantly more common in a group of pastures situated in open farmland, while only five (22%) species occurred in higher densities in pastures characterised by a high proportion of forest along the borders. Fifteen (83%) of the 18 species occurring in both pasture groups showed significant habitat-abundance relationships related to the management of semi-natural pastures, although in different directions and to different extents. Our results suggest that many farmland bird species require two important factors for their choice of breeding habitat, namely safe nest sites close to good foraging areas. Both factors are partly under the control of farmers and should be invoked in conservation strategies since many farmland birds are declining across Europe. To benefit the conservation of farmland birds in Sweden one should, in contrast to the present botanical-based subsidy scheme, retain ⩾10% cover of shrubs within pastures and preferentially select pastures in open farmland (i.e. potentially safer nesting sites with better food conditions) for restoration and management plans.

GRAZING EFFECTS ON BETWEEN‐YEAR VARIATION OF FARMLAND BIRD COMMUNITIES

Livestock grazing is the dominant land use in the remaining seminatural grasslands in Europe. Abandonment of grasslands and, conversely, intensified grazing by livestock have been suggested as possible causes for the widespread population declines of many farmland birds, although the direct impact of grazing on farmland birds is poorly known. Here, we use a comprehensive, long-term data set (20 pastures surveyed over five years) to test the effects of changes in grazing intensities in seminatural dry pastures on between-year variation of the farmland bird community, functional groups of species, and individual species. Bird communities in all 20 seminatural pastures showed a low degree of temporal variability (Kendalls coefficient of concordance on ranked abundances: mean W = 0.72, range = 0.58–0.89). Community variability was not significantly related to site area, grazing pressure, vegetation structure, or adjacent habitat composition. However, analyses of functional groups of species categorized accor...

Effects of urban matrix on reproductive performance of Great Tit (Parus major) in urban woodlands

In urban areas the density of breeding tits (Paridae) is generally higher and reproductive performance lower compared to rural areas. To explain these landscape differences several hypotheses have been proposed, e.g. differences in habitat quality, inter- and intra-specific competition, predation and food abundance. How breeding performance of birds within remnants of natural vegetation in urban areas is affected by adjacent matrix has been less studied. We performed an experimental study in four urban woodlands surrounded by three types of habitat matrix: residential, high-rise building and grassland/golf course. We placed 300 nest boxes for tits (great tit Parus major and blue tit Cyanistes caeruleus) in 15 transects that were 200xa0m long, extending from the adjacent matrix 150xa0m into urban woodland. Density of breeding great tit pairs was highest in residential areas and hatch date was earlier in the residential habitat compared to the other two habitats, however, nestling condition was lower in residential areas. Hatching date was earlier but hatching spread (heaviest nestling/lightest nestling) higher in the three types of urban matrix than inside the urban woodlands. In contrast to previous large-scale comparisons of urban and rural matrix, we almost exclusively found differences in qualitative measures (nestling condition and hatchling spread) at the small scale in which this study was conducted. Adjacent matrix affect great tits breeding in remnant urban woodlands, thus we suggest that management of the surrounding matrix should be included in conservation plans for urban woodlands.