Abstract
Vegetated roofs are human-manufactured ecosystems and potentially promising conservation tools for various taxa and habitats. Focussing on arthropods, we conducted a 3 year study on newly constructed vegetated roofs with shallow substrates (up to 10 cm) and vegetation established with pre-grown mats, plug plants and seeds to describe pioneer arthropod communities on roofs and to compare them with ground level communities. We vacuum sampled arthropods from the roofs and nearby ground level sites with low, open vegetation, i.e., potential source habitats. We showed that the roofs and ground sites resembled each other for ordinal species richness but differed in community composition: with time the roofs started to resemble each other rather than their closest ground level habitats. Species richness increased with time on roofs and at ground level, but the roofs had consistently less species than the ground sites and only a few species were unique to the roofs. Also, the proportion of predators increased on roofs, while not at ground level. We conclude that vegetated roofs established with similar substrates and vegetation, filter arthropods in a way that produces novel communities that are different from those at ground level but similar to one another. The role of these insular communities in species networks and ecosystem function remains to be investigated.
Highlights
Urbanization shrinks and fragments the living space for animals and plants by replacing natural habitats with artificial impervious surfaces, such as roads and buildings, with a pace that is projected to accelerate in the coming decades (Seto et al, 2012; McDonald et al, 2020)
The roofs we studied seemed to filter arthropods in a similar way as the roof communities became more similar with time, while at ground level community variance increased with time
Frequent drought stress that is typical for vegetated roofs with shallow substrates (Köhler and Poll, 2010) should decrease stability of arthropods communities (Tsafack et al, 2019), but we suggest that the importance of stochasticity in species occurrences and in temporal community patterns of new vegetated roofs is connected to roof size
Summary
Urbanization shrinks and fragments the living space for animals and plants by replacing natural habitats with artificial impervious surfaces, such as roads and buildings, with a pace that is projected to accelerate in the coming decades (Seto et al, 2012; McDonald et al, 2020). Arthropod Communities on Vegetated Roofs (see Kotze et al, 2020), called green roofs, are urban greening tools that preserve and restore vegetation in built areas. They mitigate a wide range of environmental problems related to urbanization, as they, e.g., reduce the urban heat island effect, contribute to stormwater management and have a positive effect on air quality (Oberndorfer et al, 2007). Describing the arthropod fauna of new roofs and their sources can be critical to understand patterns in arthropod richness and community composition in these artificial habitats
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