Arthropod Communities on Young Vegetated Roofs Are More Similar to Each Other Than to Communities at Ground Level

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.

Urban green roofs can support a diversity of parasitoid wasps

“…Our finding of increased diversity with increased age of the green roof is mirrored by some previous studies of taxa on green roofs, but differs from other studies. Some predatory arthropod taxa, including parasitoid Hymenoptera, have been shown to increase in diversity with roof age for young roofs less than 4 years of age (Kyrö et al, 2022). Also in support of the idea that biodiversity can correlate with age, a study on green roofs in Argentina found that roof age was correlated with abundance of insect predators, which included parasitoid wasps (Fabian et al, 2021(Fabian et al, ).…”

Comparing arthropod communities on two types of extensive green roofs

“…Many of the investigated conventional green roofs lacked the presence of grasses and, consequently, declaring that green roofs do contribute to the conservation of this species in urban environments is too premature. Other studies also stated that green roofs are mainly colonized by species that are common in the surrounding environment [53]. Green roofs continue to gain popularity, but more research is warranted to elucidate their role in conserving urban biodiversity.…”

“…Other variables, besides the vegetation or substrate depth, are known to affect green roof arthropod communities. For example, arthropod species richness has been found to increase in older green roofs [53], but also the height on which the green roofs are installed has been found to exert an effect on the associated spider communities [6,16,18]. Plotting the species richness of all roofs against the variables 'age', 'city', 'height', or 'size' in univariate analyses did, however, not result in signi cant correlations (Fig.…”

Assessing Ecological Gains: A Review of How Arthropods, Bats and Birds Benefit from Green Roofs and Walls

“…However, the roofs consistently hosted fewer species compared to the ground sites, and only a few species were unique to the roofs. Additionally, the proportion of predators increased on the roofs but not at ground level [37].…”

“…The following supporting information can be downloaded at: https:// www.mdpi.com/article/10.3390/environments11040076/s1, Table S1: Papers on arthropods, bats and birds used to understand how green roofs and walls can contribute to urban biodiversity. References [18,19,21,22,[24][25][26][27][29][30][31][32][33][34][35][36][37] are cited in the Supplementary Materials.…”