Green walls as refuges for arthropods in urban landscapes: Understanding diversity drivers and ecological networks

Abstract

The main drivers of biodiversity decline and changes in arthropod species assemblages are fragmentation and habitat loss caused by land-use changes in urbanized landscapes. While the effect of urbanisation on arthropods has received more attention in the past, the effects of green walls in mitigating the diversity crisis and their ecosystems services remain largely unquantified as moststudies were either focused on the thermal/technical values or entirely on green roofs. To comprehensively assess the effects of green walls on arthropods, we sampled arthropods on 9 living walls (LWs) and 5 green facades (GFs) at 5 locations in the Randstad region of the Netherlands. Specimens were identified to the family level. The study specifically focused on the effects of local habitat characteristics of varying wall and plant characteristics (e.g. wall area, age, aspect, botanical composition, plant density and richness etc.) and investigated the landscape level effect of urbanization through the blue/green/grey area composition in 20-, 100-, 200- and 500-meter radii around the sampling points. We first compared LW and GF to their control counterparts and to each other. Secondly, we tested for the effects of locallandscape level characteristics on arthropod abundance, richness, diversity, and community composition using uni- andmultivariate analysis, linear models, and canonical correspondence analysis (CCA). Lastly, we explore ecological networks and relationships that are taking place on LW. Neither LW nor GF host more abundance, richness or diversity. However, both wall types seem to foster a unique arthropod composition, respectively indicating high ecological value. Results show that both local- and landscape-level characteristics influence the research metrics. Especially, the number of flowering plants positively correlates with arthropod diversity and abundance of flower visiting orders. Furthermore, high proportions of waterbodies and green areas positively correlate with abundance, richness and diversity. Arthropod orders and families were affected differently by local and landscapelevel variables and a variety of intricate ecological relationships were uncovered. This accentuates the importance of considering a lower-taxonomic relationships as well as a variety of local and landscapelevel factors when designing green infrastructures thataim to aid the current arthropod diversity crisis.