Estimation and prediction of plant species richness in a mosaic landscape

Traditional agricultural mosaic landscapes are likely to undergo dramatic changes through either intensification or abandonment of land use. Both developmental trends may negatively affect the vascular plant species richness of such landscapes. Therefore, sustainable land-use systems need to be developed to maintain and re-establish species richness at various spatial scales. To evaluate the sustainability of specific land-use systems, we need approaches for the effective assessment of the present species richness and models that can predict the effects on species richness as realistically as possible. In this context, we present a methodology to estimate and predict vascular plant species richness at the local and the regional scale. In our approach, the major determinants of vascular plant species richness within the study area are taken into consideration: These are according to Duelli's mosaic concept the number of habitat types and of habitat patches within area units. Furthermore, it is based on the relative frequencies of species within habitat types. Our approach comprises six steps: (i) the determination of present habitat patterns within an observation area, (ii) the creation of a land-use scenario with simulated habitat patterns, (iii) the determination of species frequencies within habitat types of this area, (iv) a grouping of habitat-specific species, (v) the estimation of the probabilities for all species (or habitat specialists) to occur, either in stepwise, exponentially enlarged landscape tracts (local scale), or in the entire observation area (regional scale), and (vi) the validation of the estimated species numbers. The approach will be exemplified using data from the municipal district of Erda, Lahn-Dill Highlands, Germany. The current species numbers to be expected on the basis of probability calculations were compared with those recorded on the basis of extensive field work. This comparison shows that, on the basis of our simple calculations, the current local plant species richness can be predicted well, with a slight underestimation. This revised version was published online in May 2005 with corrections to the Cover Date. This revised version was published online in July 2006 with corrections to the Cover Date.     

Quantifying determinants contributing to plant species richness in mosaic landscapes: a single- and multi-patch perspective

Despite good theoretical knowledge about determinants of plant species richness in mosaic landscapes, validations based on complete surveys are scarce. We conducted a case study in a highly fragmented, traditional agricultural landscape. In 199 patches of 20 representative multi-patch-plots (MPPs, 1 ha) we recorded a total of 371 plant species. In addition to an additive partitioning of species diversity at the (a) patch- and (b) MPP-scale, we adopted the recently proposed ‘specificity’ measure to quantify the contribution of a spatial subunit to landscape species richness (subunit-to-landscape-contribution, SLC). SLC-values were calculated at both scales with respect to various spatial extents. General regression models were used to quantify the relative importance of hypothesis-driven determinants for species richness and SLC-values. At the patch scale, habitat type was the main determinant of species richness, followed by area and elongated shape. For SLC-values, area was more important than habitat type, and its relevance increased with the extent of the considered landscape. Influences of elongated shape and vegetation context were minor. Differences between habitat types were pronounced for species richness and also partly scale-dependent for SLC-values. Relevant predictors at the MPP-scale were nonlinear habitat richness, the gradient from anthropogenic to seminatural vegetation, and the proportions of natural vegetation and rare habitats. Linear elements and habitat configuration did not contribute to species richness and SLC. Results at the MPP-scale were in complete accordance with the predictions of the mosaic concept. Hence, our study represents its first empirical validation for plant species diversity in mosaic landscapes.     

Determinants of plant species richness and patterns of nestedness in fragmented landscapes: evidence from land-bridge islands

Land-bridge islands formed by dam construction are considered to be “experimental” systems for studying the effects of habitat loss and fragmentation, offering many distinct advantages over terrestrial fragments. The Thousand Island Lake in Southeast China is one such land-bridge system with more than 1000 islands. Based on a field survey of vascular plant richness on 154 land-bridge islands during 2007–2008, we examined the effects of island and landscape attributes on plant species richness and patterns of species nestedness. We also examined the different responses of plant functional groups (classified according to growth form and shade tolerance) to fragmentation. We found that island area explained the greatest amount of variation in plant species richness. Island area and shape index positively affected species diversity and the degree of nestedness exhibited by plant communities while the perimeter to area ratio of the islands had a negative effect. Shade-tolerant plants were the most sensitive species group to habitat fragmentation. Isolation negatively affected the degree of nestedness in herb and shade-intolerant plants including species with various dispersal abilities in the fragmented landscape. Based on these results, we concluded that the effects of habitat loss and fragmentation on overall species richness depended mostly on the degree of habitat loss, but patterns of nestedness were generated from different ecological mechanisms due to species-specific responses to different characteristics of habitat patches.     

The role of landscape structure in species richness distribution of birds,amphibians, reptiles and lepidopterans in Mediterranean landscapes

The parameters referring to landscape structure are essential in any evaluation for conservation because of the relationship that exists between the landscape structure and the ecological processes. This paper presents a study of the relationships between landscape structure and species diversity distribution (estimated in terms of richness of birds, amphibians, reptiles and butterflies) in the region of Madrid, Spain. The results show that the response of species richness to landscape heterogeneity varies depending on the group of species considered. For birds and lepidopterans, the most important factor affecting the distribution of richness of species is landscape heterogeneity, while other factors, such as the specific composition of land use, play a secondary role at this scale. On the other hand, richness of amphibians and reptiles is more closely related to the abundance of certain land-use types. The study highlights the importance of heterogeneity in Mediterranean landscapes as a criterion for landscape planning and for definition of management directives in order to maintain biodiversity.     

The influence of management history and habitat on plant species richness in a rural hemiboreal landscape,Sweden

We explored patterns of plant species richness at different spatialscales in 14 habitats in a Swedish rural landscape. Effects of physicalconditions, and relationships between species richness and management historyreaching back to the 17^th century were examined, using old cadastralmaps andaerial photographs. The most species-rich habitats were dry open semi-naturalgrasslands, midfield islets and road verges. Alpha diversity (species richnesswithin sites) was highest in habitats on dry substrates (excluding bedrock withsparse pines) and beta diversity (species richness among sites) was highest inmoist to wet habitats. Alpha and beta components of species richness tended tobe inversely related among habitats with similar species richness. Managementhistory influenced diversity patterns. Areas managed as grasslands in the17^th and 18^th century harboured more species than areasoutside the villages. We also found significant relationships between speciesrichness and soil type. Silt proved to be the most species-rich topsoil(10–20 cm) in addition to thin soils top of on green- orlimestone bedrock. The variation in species richness due to local relief orform of thesite also showed significant relationships, where flat surfaces had the highestnumber of species. In contrast, no significant relationship was found betweenspecies richness and aspect. Our study suggests that present-day diversitypatterns are much influenced by management history, and that small habitat,e.g., road verges and midfield islets, are important for maintaining speciesrichness.This revised version was published online in May 2005 with corrections to the Cover Date.     

Non-linear effects of landscape on pollination service and plant species richness in a peri-urban territory with urban and agricultural land use

Pollination contributes to both human food security and the reproduction of the majority of wild plant species, but pollinators are facing a rapid decline, a major cause of which is habitat conversion and degradation due to human activities. Urbanization is one of the major types of habitat conversion, but its influence on pollination has been surprisingly mixed, ranging from markedly negative to strongly positive effects. One hypothesis proposed to explain these discrepancies is that pollinator responses to urbanization are highly dependent on the non-urban control habitat, with negative effects when the controls are natural or semi-natural areas but positive when they are intensive agricultural areas. It was also proposed that the pollination response along an agricultural-to-urban gradient is non-linear, with maximum pollination observed at an intermediate level of urbanization due to increased environmental heterogeneity. To test these two hypotheses, we selected a group of 38 sites in a peri-urban area near Paris, France, using a semi-stratified sampling strategy that ensured that all three of the urban, agricultural and semi-natural gradients were maximized. We then estimated pollination using two approaches: we evaluated the pollination success of Lotus corniculatus, a strictly entomogamous self-sterile plant species pollinated mainly by bees, and we measured the species richness of entomogamous and non-entomogamous plants, the difference in their response being expected to relate to the pollination service provided by the overall pollinator community. We found that in our study area, pollination success of L. corniculatus responds positively to the agricultural to urban gradient but not to the semi-natural to urban gradient. The diversity of both entomogamous and non-entomogamous plants is highest at sites surrounded by intermediate proportions of urban and agricultural areas. In addition, high proportions of urban areas have a negative effect on the diversity of non-entomogamous but not entomogamous plant species, suggesting that pollinators are able to partially buffer entomogamous plant species against the negative effect of urban development. Our results show the importance of urban areas in pollination conservation plans and demonstrate that the interaction between different anthropogenic land-use is an important factor for understanding pollination.