Native plants on experimental urban green roofs support higher community-level insect abundance than exotics

Abstract

Urbanization is one of the multiple factors leading to global insect declines. As urbanization grows, green roofs represent a nature-based solution that could provide habitat for plants and animals within cities. Several characteristics of green roofs could enhance insect biodiversity. Nevertheless, little is known about the effects of plant origin on insect abundance from a multi-taxa perspective. Thus, our main goal was to evaluate the effects of plant origin, local resources, and urbanization level on green roofs’ overall insect abundance, the abundance of different taxonomic orders, and community composition. Using experimental green roofs, we compared insect communities between native and exotic plants across an urbanization gradient, in Córdoba city, central Argentina. On the roofs of 30 houses, we installed two blocks of a modular extensive green roof system, with either native or exotic plant species (6 species each). In March 2019, we used yellow pan traps and pitfall traps (N = 360) to sample insects and measured flower abundance and plant cover at each plant treatment. The urbanization level of each house was estimated by the Normalized Difference Vegetation Index (NDVI), the Normalized Difference Built-up Index (NDBI), and the Land Surface Temperature (LST). A total of 35,257 insects from 12 orders were registered, with Diptera, Hymenoptera, and Hemiptera as the dominant groups. Native plants supported significantly higher total insect abundance on both types of traps, independently from the urbanization level, flower abundance, or plant cover of each roof. The abundance of most of the taxonomic orders was higher in natives as well, but particular effects of the covariables were detected for certain groups. In addition, plant origin was an important factor for insect composition. Our results highlight that green roof design should prioritize native plants to enhance insect conservation while achieving more sustainable cities.