Responses of grassland species richness to local and landscape factors depend on spatial scale and habitat specialization

Abstract

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.

Linking landscape history and dispersal traits in grassland plant communities

“…The significant association between species composition in old grassland sites and the distribution of dispersal sources in the historical landscape may reflect a time lag in species' response to habitat fragmentation (e.g., Helm et al 2006). Plant species composition in grazed, previously arable (young) sites has also been shown to be dependent on the proximity to seminatural grasslands in the historical landscape (Cousins and Aggemyr 2008;Reitalu et al 2011), suggesting that grassland species have accumulated in the surrounding landscape over long periods of continuous grazing management.…”

The relationship between landscape configuration and plant species richness in forests is dependent on habitat preferences of species

“…4 Relationship between forest area and species richness of forest plant species in a small and b large plots (linear mixedeffects model, n.s. in both cases) and effect of length of forest edge on species richness of edge plant species in c small and d large plots with 95 % confidence bands (dashed lines) calculated from linear mixedeffects model Reitalu et al (2012) found a positive habitat area effect on species richness on a large plot scale (0.1-4.8 ha polygons), but there was no significant area effect on species richness at a small plot scale (0.25 m 2 ). This was true both for grassland specialist species and for generalist species.…”

Floral Resources Sustaining African Meliponine Bee Species (Hymenoptera: Meliponini) in a Fragile Habitat of Kenya

“…The hills are isolated from other mountainous areas to the south-east (Shimba Hills), south (Usambara Mountains), south-west (Mt Kilimanjaro), west (Ngulia and Chyulu Hills) and north-west (Kenyan highlands) by the vast plains of Tsavo (Maeda et al, 2010). Annual rainfall is received during two major seasons (March-May, September -October) and varies between 480 -1200mm in the highlands (Reitalu et al, 2012), but much less rain (̴̴ ̴̴ 400mm) received on the surrounding plains of the lowlands (Pellikka et al, 2005).…”