Green roofs are often promoted as a mean to counter the negative environmental effects of urbanization on nature and to increase the amount of green space in cities. Green roofs often enhance aboveground biodiversity, especially herbivores and pollinators. However, if and in what way they support belowground biodiversity, and more specifically soil fauna, is rarely studied. Therefore, we evaluated the diversity of a dominant group of soil fauna, Collembola (springtails), on twelve extensive green roofs in three cities in Belgium (Antwerp, Ghent and Hasselt), over a one year period. The roofs differed in height above the ground, surface area, vegetation type, and age, i.e. time since construction. We analysed if these roof characteristics influenced species richness, abundance or diversity of Collembola. In total we found ten species of Collembola. Species richness was not higher on roofs that were larger (habitat area) or closer to the ground (isolation to surrounding soil), indicating that island-biogeographic theory is not applicable to species richness in our study system. However, significant differences in the mean number of individuals (abundance) were found between different months. Collembola taxonomical composition also varied between the roofs, but this variation could not be related to any of the measured roof variables. Roof communities were characterised by hemiedaphic life forms, preferring neutral to semi-moist conditions. Apart from the age of the roof that showed a positive significant impact on the abundance of Collembola present, our results suggested that the collembolan fauna showed no significant differences in abundance, species richness or diversity between roofs with different characteristics. However, we suggest that future studies are needed to investigate whether our findings are applicable to other groups of soil-living arthropods on green roofs.

Dr Jeffrey Jacobs Master of science: evolution en behavioural-biology
PhD Research project: Biodiversity on urban green roofs: a focus on macro-invertebrates
Hisresearch focuses on assessing the biodiversity on green roofs. Green roofs have potential for providing substantial habitat to plants, birds, and arthropod species that are not well supported by other urban habitats. Whereas the plants on a typical green roof are chosen and planted by people, the arthropods that colonize it can serve as an indicator of the ability of this novel habitat to support a diverse community of organisms.
In the first part of my PhD he focussed on belowground biodiversity, which was assessed for a deliberately chosen group of soil arthropods: the springtails (Collembola). Collembola are among the most abundant and widespread terrestrial arthropods, and are important in many soil functions such as litter decomposition and nutrient cycling. However, what explains their diversity and species composition in isolated, small habitat fragments is less known.
Furthermore, are we currently investigating multiple green roofs in the city of Antwerp (Belgium) and focussing on the aboveground macro-invertebrates that live on them (main focus wild bees). This research has the potential to contribute to the academic understanding of biodiversity on green roofs, but more than this, it may have an impact on wider society. With worldwide increasing urbanization it is crucial that we understand how we can counteract the loss of biodiversity in urban areas. Green roofs are seen as the number one method to get more green spaces in cities, however there is a lack of studies in Belgium on green roofs and how they can support biodiversity. We hope that by doing so we can derive main principles regarding the design of green roofs with the aim of maximizing their macro-invertebrate biodiversity.