Shading enhances plant species richness and diversity on an extensive green roof
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Shading enhances plant species richness and diversity on an extensive green roof Henk-Jan van der Kolk 1
&
Petra van den Berg 1 & Gerard Korthals 1 & T. Martijn Bezemer 1,2
# The Author(s) 2020
Abstract Green roofs can promote biodiversity in urban areas. The extent to which green roofs stimulate plant diversity can depend on roof characteristics such as roof age, substrate depth and shading. We exploratively studied the vegetation on a Dutch green roof in 50 permanent plots (1 m2) over eight years (2012–2019) following roof construction. Plots were situated either on low substrate depth (6 cm light-weight extensive substrate) or high substrate depth (6 cm light-weight extensive substrate topped with 14 cm native soil) and differed in the amount of shading received from a higher building floor. Increased substrate depth and shading additively increased plant species richness and plant diversity, with high shaded plots supporting on average 6.4 more plant species than low unshaded plots. Shading likely acts via reducing drought stress, whereas increasing substrate depth with native soil may also enhance plant diversity via addition of nutrients and native seeds. The vegetation composition on the roof was dynamic and changed over the years. Sedum acre was initially dominant but disappeared within the first years, whereas Sedum kamtschaticum increased and became dominant in the last years. Trifolium arvense was the most abundant forb species and was especially dominant three years after roof construction. We conclude that increased substrate depth and shading can promote plant species richness and diversity and recommend that both aspects are considered when green roofs are designed. Shading can be achieved by a stepped building architecture and by placing structures on the roof itself, such as solar panels on standards. Keywords Biodiversity . Green roof . Microclimate . Succulents . Urban ecology . Vegetation
Introduction Green roofs are increasingly popular in urban areas since they provide a range of benefits including retention of rainwater, cooling of buildings and promoting biodiversity (Oberndorfer et al. 2007; Berardi et al. 2014; Filazzola et al. 2019). Biodiversity is promoted on green roofs by the higher presence and abundance of native plant species and arthropods compared to conventional roofs (Madre et al. 2013, 2014; Schrader and Böning 2006). Some green roofs harbour plant species that are locally rare or Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11252-020-00980-w) contains supplementary material, which is available to authorized users. * Henk-Jan van der Kolk [email protected] 1
Netherlands Institute of Ecology, Wageningen, The Netherlands
2
Institute of Biology, Section Plant Ecology and Phytochemistry, Leiden University, Leiden, The Netherlands
endangered, which emphasises their potential to enhance biodiversity in urban areas (Gabrych et al. 2016). Green roofs vary largely in their design, complexity and vegetation structure, bu
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