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Abstract: In arid and semi-arid regions water availability is the main factor determining vegetation patterns. On gypsum outcrops, vegetation is also conditioned by soil physical (i.e. surface crust) and chemical (i.e. ion unbalance) restrictions, which promote a highly specialist and endemic gypsophile flora. Topographical and climatic variability affect the rigors of gypsum soil environment, and thus, plant community distribution along environmental gradients can differ between gypsum and non-gypsum substrates. The aim of the paper was to evaluate the relative importance of different abiotic factors as drivers of plant communities in gypsum and non-gypsum substrates. While non-gypsophile vegetation is expected to be determined mainly by aridity, gypsophile vegetation could show more complex patterns, following the relaxation of the rigors of gypsum soil under environmental gradients such as steep slopes and mesic conditions. We compared the relationships between presence and cover of three plant communities (open woodland, dwarf-shrubland and garrigue) on gypsum and non-gypsum substrates with environmental factors, after removing the effect of human use. Generalized additive models (GAM) and generalized linear models (GLM) were employed. Results showed that xeric conditions inhibited development and recovery of vegetation, but plant communities on gypsum substrate did not always respond in the same way as non-gypsum vegetation. While the degree of aridity (determined by precipitation and temperature) conditioned non-gypsum vegetation strongly, favouring less developed plant communities, topographical factors (slope aspect and angle) were the main determinants of gypsum plant community patterns. We conclude that gypsum substrate determines strongly the plant community patterns in a semi-arid Mediterranean landscape, as it can be observed by the strong response of gypsophile vegetation to the relaxation of the rigors of gypsum soils with topography (i.e. steep and north oriented slopes). [Copyright &y& Elsevier]

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• Effect of grazing on soil hydraulic properties of gypseous soils were studied. • Three grazing intensities, High, Medium and Low, were compared. • Soil surface S and K c and subsurface ρ b , K s , θ s , α and n were measured. • H presented the highest ρ b and the lowest K c values. • In semiarid gypseous soils M did not have a negative effect of soil properties. Although is well known that grazing has a significant effect on the soil hydraulic properties and through them on the pasture productivity in semi-arid regions, there is still little data about the effect of this management on soils with high gypsum content. This work compares the effect of three increasing grazing intensities (low, medium, and high) on the hydraulic properties of the upper soil layers, measured on two areas with increasing gypsum content (56 and 73%, respectively) located in a semi-arid region of the Middle Ebro Valley (NE, Spain). 90 soil samplings were taken on bare soil surface areas. The measured soil parameters included the saturated sorptivity (S c) and hydraulic conductivity (K c) of the soil surface layer and the soil bulk density (ρ b), saturated hydraulic conductivity (K s), saturated volumetric water content, θ s , and α and n parameters of the water retention curve of the 1–8 cm depth soil layer. Increasing gypsum content increased the soil water infiltration but did not affect the water retention capacity and total porosity. All studied gypseous soils presented low water retention. High grazing intensities decreased the soil water infiltration. While soils with high gypsum content tended to attenuate the effect of the livestock trampling on ρ b , a significant influence of grazing on ρ b was observed in the fields with moderate soil gypsum content. No effect of livestock trampling on the soil water retention characteristics was observed. Moderate grazing, which did not show negative effects on the soil hydro-physical properties, could be an acceptable management for soil conservation in these semiarid regions of soils with high gypsum content. [ABSTRACT FROM AUTHOR]