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After foundation of the Wadden Sea National Park, grazing and artificial drainage was ceased or reduced on large areas of the salt marshes at the Schleswig-Holstein mainland coast (Northern Germany). The effect of grazing cessation versus intensive and moderate grazing on vegetation diversity was studied on small (plant species richness on plots between 0.01 and 100 m2) and large scale (vegetation type richness per hectare) over 18 to 20 years by analysing data from long-term monitoring programs. Plant species richness and vegetation type richness increased strongly over time in all management regimes, because grazing-sensitive species increased first in ungrazed marshes and later dispersed to and established in intensively grazed marshes. Dominance of the tall, late-successional grass Elymus athericus on 7% to 52% of all moderately and ungrazed (primarily high marsh) plots led to a decrease in species richness. After 18 to 20 years, species richness was highest in moderately and intensively grazed high marshes. Differences were significant only on small plots of up to 4 m2. On the large scale, vegetation type richness in the low marsh was higher without grazing, while no differences were found in the high marsh. Our results indicate that grazing effects differ between spatial scales and that different spatial scales have to be considered for monitoring and evaluation of vegetation diversity in salt marshes. To conserve vegetation diversity on all scales, a large-scale mosaic of different management regimes should be maintained.
Green roofs are known to mitigate the negative effects of urban consolidation by offering diverse ecosystem functions compared to non-vegetated roofs. However, the support for native biodiversity might be improved by using native plant species. In a mesocosm experiment, we studied the suitability of three commercial green-roof growth substrates for the establishment of 27 native plant species from dry sandy grasslands of northwestern Germany over the course of four years. The substrates were mineral-based, but differed in the layering of organic matter. Total establishment rates reached 44–59% in Year 4, indicating the general suitability of the substrates. During the first weeks after seeding, with light irrigation, the vascular plant cover was greater in the similar substrates Zincolit® Plus (Z) and Zincolit® Plus-Leicht (ZL) with their compost-based organic mulch layers than in the substrate Sedumteppich (ST) with its organic matter evenly admixed with the mineral aggregates. In Years 2 and 3, however, the vascular plant cover was greater in the ST substrate, likely due to the better availability of water and nutrients from the organic matter compared to the dry surface-mulch layer variants Z and ZL. After severe drought events, the decline in plant cover was more pronounced in the ST substrate, likely representing a trade-off between lush growth and a susceptibility to drought. An indicator-species analysis revealed differences in species composition between the ST and Z/ZL substrates. Annual plant species were indicators of the ST substrate. Perennials, such as Thymus pulegioides and Achillea millefolium, were typical of the Z and ZL substrates. In addition to the general suitability of the tested standard substrates for target species establishment, the study indicated that a combination of different layers of substrate components resulted in different vegetation patterns that may have a positive effect on green-roof biodiversity.