Beta diversity patterns are essential for understanding how biological communities are structured. Geographical and environmental factors, as well as species dispersal ability, are important drivers of beta diversity, but their relative importance may vary across spatial scales. In this study, we evaluate whether beta diversity changes across geographical scales and analyse how different drivers affect turnover patterns of native seed plants in an oceanic archipelago, the Azores (Portugal). Using a 500 x 500 m resolution grid, we selected cells that are covered by one of the following habitats: native forest, naturalized vegetation and seminatural pastures. We calculated species turnover at three spatial scales: i) between islands, ii) between cells within each island, and finally iii) between cells of each of the habitats of interest in each island. We then calculated the contribution of dispersal syndromes (endozoochory, epizoochory, hydrochory and anemochory) to turnover at each of the scales. Lastly, we assessed the relationship between geographical and climatic distances and habitat composition with turnover. Turnover was higher at the smallest scale, particularly in seminatural pastures, and decreased with increasing spatial scales, a pattern potentially associated with the historical fragmentation and current patchy distribution of native forest and seminatural habitats in the Azores. Dispersal syndromes and habitat composition had a negligible effect on turnover at all scales. Geographical distance had a positive effect on turnover at all scales, increasing with scale. The relationship between turnover and climatic distance was only significant at the intermediate and small scales in specific islands and habitats. Scale plays an important role at determining the effect of the drivers of turnover, in particular geographical and climatic distance. These results highlight the need to carefully select the scale of analysis when studying turnover patterns, as well as identifying the potential drivers associated with each scale.

Aim: Species’ environmental requirements and large-scale spatial and evolutionary processes are known to determine the structure and composition of local communities. However, ecological interactions and historical processes also have major effects on community assembly at landscape and local scales. In this work we evaluate whether two xerophytic shrub communities follow fixed ecological assembly dynamics throughout large geographical extents, or their composition is rather driven by species individualistic responses to environmental and macroecological constraints. Location: SW Iberian Peninsula (Portugal and Spain) Taxa: Stauracanthus genistoides agg. and Ulex australis agg (Fabaceae). Methods:Inland dune xerophytic shrub communities were sampled in 95 plots distributed within their potential area of occurrence. Then, we described the main gradients of vegetation composition and assess the relevance of biotic interactions. We also characterized the habitat suitability of the dominant species, S. genistoides and U. australis, to map the potential distribution of the xerophytic shrub communities. Finally, to identify the relative importance of each factor driving changes in community composition, we examined the relationships between the vegetation gradients and a broad set of explanatory variables. Results: Our results show that xerophytic shrubs follow uniform successional patterns throughout the whole geographical area, but also that these communities respond differently to the main environmental gradients in each region. Soil organic matter is the main determinant of community variations in the northern regions, Setúbal Peninsula and Comporta, while in the South/South-Western region most of the variation between both types of communities is explained by temperature seasonality. Main conclusions: The relative importance of the main factors causing community-level responses varies according to regional processes and the suitability of the environmental conditions for the dominant species in these communities. These responses are also determined by intrinsic community mechanisms that result in a high degree of similarity in the gradient-driven community stages in different regions.