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Question: We studied the patterns of plant species co‐occurrence on three, nested, spatial scales in semi‐natural grassland communities and explored the possible ecological processes underlying the patterns. Location: Dry, semi‐natural grasslands in a 4.5 km x 4.5 km area on the Baltic Island of Oland (Sweden). Methods: The study used replicated samples on three, nested, spatial scales: 50 cm x 50 cm plots (N= 516), grassland patches (N = 109) and the whole landscape (N= 6). We used a null model approach to study species co‐occurrence patterns and compared the ecological amplitudes of the pairs of species contributing most to the patterns. We used linear models to search for associations between species segregation and environmental and landscape factors. Results and Conclusions: Our results support the prediction that patterns of species co‐occurrence are likely to be influenced by different mechanisms on different spatial scales. On the plot scale, we interpreted the species segregation in terms of species interactions. The degree of species segregation was significantly associated with the plots'positions within the grassland patches (edge effects) and with management intensity of the grasslands ‐ both variables can be assumed to influence species interactions. On the grassland patch scale, we interpreted the species segregation in terms of within‐patch environmental heterogeneity. The degree of segregation was significantly associated with the area of the grassland patches and with management intensity ‐ both variables that are likely to be related to environmental heterogeneity within the grasslands. Species segregation on the landscape scale was interpreted in terms of environmental heterogeneity among grassland patches and was significantly associated with land‐use history.

Semi-natural grasslands with grazing management are characterized by high fine-scale species richness and have a high conservation value. The fact that fine-scale surveys of grassland plant communities are time-consuming may limit the spatial extent of ground-based diversity surveys. Remote sensing tools have the potential to support field-based sampling and, if remote sensing data are able to identify grassland sites that are likely to support relatively higher or lower levels of species diversity, then field sampling efforts could be directed towards sites that are of potential conservation interest. In the present study, we examined whether aerial hyperspectral (414-2501 nm) remote sensing can be used to predict fine-scale plant species diversity (characterized as species richness and Simpson's diversity) in dry grazed grasslands. Vascular plant species were recorded within 104 (4 mˆ4 m) plots on the island of Öland (Sweden) and each plot was characterized by a 245-waveband hyperspectral data set. We used two different modeling approaches to evaluate the ability of the airborne spectral measurements to predict within-plot species diversity: (1) a spectral response approach, based on reflectance information from (i) all wavebands, and (ii) a subset of wavebands, analyzed with a partial least squares regression model, and (2) a spectral heterogeneity approach, based on the mean distance to the spectral centroid in an ordinary least squares regression model. Species diversity was successfully predicted by the spectral response approach (with an error of ca. 20%) but not by the spectral heterogeneity approach. When using the spectral response approach, iterative selection of important wavebands for the prediction of the diversity measures simplified the model but did not improve its predictive quality (prediction error). Wavebands sensitive to plant pigment content (400-700 nm) and to vegetation structural properties, such as above-ground biomass (700-1300 nm), were identified as being the most important predictors of plant species diversity. We conclude that hyperspectral remote sensing technology is able to identify fine-scale variation in grassland diversity and has a potential use as a tool in surveys of grassland plant diversity.

Questions To what extent is species richness in semi‐natural grasslands related to local environmental factors and (present/past) surrounding landscape structure? Do responses of species richness depend on degree of habitat specialization (specialists vs generalists) and/or scale of the study? Location Öland, Sweden. Methods Richness of herbaceous vascular plants (subdivided into richness of grassland specialists and generalists) was recorded within 50 × 50 cm plots and 0.1–4.8 ha grassland polygons. Generalized linear models and hierarchical partitioning were used to identify local factors (habitat area and heterogeneity, grazing intensity, habitat continuity) and landscape factors (proportion of surrounding grassland in 2004, 1938 and 1800, and landscape diversity in 2004) associated with the richness estimates. Results At the polygon scale, both specialist and generalist richness was positively associated with local habitat area and heterogeneity and, independently of area and heterogeneity, with grazing intensity, habitat continuity and amount of surrounding grassland in 1800. At the plot scale, specialist species richness was positively associated with habitat heterogeneity, amount of surrounding grassland in 2004 and landscape diversity. Plot‐scale generalist richness was negatively associated with surrounding grassland in 1938 and positively associated with local grazing intensity. Conclusions Because both habitat specialization and study scale influence conclusions about relationships between species richness and local and landscape factors, the study highlights the need to consider species diversity at multiple spatial scales when making decisions about grassland management. Large‐scale (polygon) species richness is influenced by immigration processes, with both specialists and generalists accumulating in old grasslands over centuries of grazing management. Habitat heterogeneity increased specialist species richness at both scales, suggesting that management policies should favour maintenance of a heterogeneous mosaic of open areas, trees and shrubs in temperate grazed grasslands. Although grassland specialists are sensitive to grassland isolation, in extensively managed landscapes with high landscape diversity input of grassland species from the landscape matrix may buffer negative effects of habitat fragmentation on grassland communities.