Ecologists have long investigated the relationships between ecosystem productivity and key drivers such as climate, species richness and soil fertility. Many valuable ecosystem services, such as carbon capture, food production, and urban climate amelioration may be directly related to biomass production by vegetation, but a new focus on ecosystem multifunctionality and services provided by urban green spaces requires attention to other potential driving factors of ecosystem services. Urban spontaneous vegetation stands out in providing habitat for diverse plant and invertebrate species, but does not perform climate regulation functions as well as lawns and urban forests. We compared predictors of habitat provisioning services (indexed by species diversity estimates) with climate regulation services (indexed by maximum soil temperature, soil organic matter and aboveground biomass) in urban spontaneous vegetation. We sampled vegetation plots at 11 sites for plant community composition, aboveground biomass, soil organic matter, nutrient content and temperature. Invertebrate diversity at each plot was quantified by pitfall trapping and sweep netting. We used general linear models to determine the best set of predictors for each variable representing an ecosystem service.
In general, invertebrate diversity variables were predicted by combinations of site area, plant alpha diversity (mean plot-level species richness), and spatial heterogeneity. In contrast, climate regulation functions were predicted by variables related to soil fertility and aboveground biomass. Total invertebrate family richness was positively related to site area and plant alpha diversity, with taxon groups (bees, beetles, butterflies, moths) showing similar patterns. Site-level plant species richness was positively related to plant alpha and beta diversity and spatial heterogeneity in soil sodium. In constrast, increases in mean soil moisture and nutrient content predicted high aboveground biomass, soil organic matter, and cooler soil temperatures. The finding that biodiversity provisioning services were predicted by contrasting drivers compared with production and climate regulation services implies that design of constructed ecosystems, such as green roofs, needs to take into account the key drivers of targeted ecosystem services. Within-site spatial heterogeneity, both abiotic and biotic (in the form of plant diversity) emerges as a potentially important driver of urban biodiversity.