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Green roofs are expected to contribute to higher biodiversity in urban surroundings. Typically, green roofs have been designed with low plant diversity. However, plant diversity can be enhanced by controlling resource availability and creating distinct niches. Here we hypothesize that by using different drainage heights during the short plant-growing season in a semi-arid green roof system we can create distinct niches and plant communities. Our experiment took place at the University of Haifa, north Israel. We tested three different heights of drainage outlet: 10 cm under the surface of the substrate (Low), 1 cm under the surface of the substrate (Medium) and 3 cm above the surface of the substrate (High) on plant species-composition in green-roof gardens. Grasses cover was higher in High and Medium drainages while forbs cover was higher in Low drainage. Species richness was the highest in Low drainage while diversity indices showed the opposite trend. We conclude that by changing the height of the drainage we can create different niches and change species composition in a short time period of one growing season. This way we can create more diverse green roof communities and enhance biodiversity in urban areas, particularly in semi-arid regions. [ABSTRACT FROM AUTHOR]

Landscape modulators are ecosystem engineers that create distinct patches that differ from their surroundings in abiotic conditions and species composition. Woody plants are principal landscape modulators in many terrestrial ecosystems. The effects of woody landscape modulators on herbaceous species richness have been studied at the site level in Israel. Here we examine the effect of woody landscape modulators on the general pattern of herbaceous species richness over a large spatial scale along a rainfall gradient, and develop a novel quantitative model to explain that pattern. A uniform experimental design was implemented at five sites along a rainfall gradient in Israel. Herbaceous species richness was determined in woody (modulated) patches and in their surrounding (unmodulated) areas, both in undisturbed (control) plots and in plots in which the canopies of the woody plants had been removed. Herbaceous species richness increased asymptotically with increasing rainfall in the unmodulated areas, but not in the modulated patches of the no-removal plots. Removal of woody plant canopies resulted in a similar pattern of herbaceous species richness to that of the unmodulated areas. Woody landscape modulators modify the pattern of herbaceous species richness along rainfall gradients by creating a biotically induced gradient of abiotic conditions, mainly via their canopy structure. The proportion of species in the site-level species pool that are filtered into the modulated patches declines in strong negative correlation with increasing LAI of the landscape modulator. The combination of climatic and biotically induced gradients determines the overall pattern of herbaceous species richness in two-phase landscape mosaics. [ABSTRACT FROM AUTHOR]

“Landscape modulators” are ecosystem engineers that have an impact on community structure by creating patches in the landscape mosaic. Our aim was to study the effect of evergreen-trees, as landscape modulators, on herbaceous plants in a Mediterranean maquis system in northern Israel. We examined the effects of canopy removal and cattle grazing on species richness, plant functional types, and rare plant species in two patch-types: (1) woody—under tree canopy (or the location of a removed canopy); (2) herbaceous—in open areas with no tree canopy. Patch-type and tree removal affected species richness and plant functional types. The extreme negative effect of the woody patch-type on species richness disappeared soon after the removal of the landscape modulator canopy. We conclude that the dominant effect of the evergreen woody landscape modulators can be regulated by canopy removal and grazing for maintaining patch-type and landscape diversities, and consequent high species richness in Mediterranean ecosystems, which is a main goal of global nature conservation policy. [ABSTRACT FROM AUTHOR]