Cities are rapidly expanding worldwide and there is an increasing urgency to protect and enhance urban biodiversity. Despite this clear guidelines of how to provide suitable habitat through the design of urban green spaces is lacking. We sampled biodiversity within the three dominant urban green space habitats, golf courses, public parks and residential neighbourhoods, in south-east Melbourne, Australia’s second largest city (population 4.5 million). These habitats have the greatest scope for design and management intervention to improve urban biodiversity. Using multi-species occupancy-detection models, we examined the taxa- and species-specific responses of five taxonomically and functionally diverse animal groups to three key attributes of urban green space vegetation that drive habitat quality and can be manipulated over time: the density of large native trees, volume of understorey vegetation and percentage of native vegetation.
We found marked differences in the effect of these vegetation attributes on bats, birds, bees, beetles and bugs. At the taxa-level, increasing the volume of understorey vegetation and percentage of native vegetation had uniformly positive effects. We found 30–120% higher occupancy for bats, native birds, beetles and bugs with an increase in understorey volume from 10 to 30%, and 10–140% higher occupancy across all native taxa with an increase in the proportion of native vegetation from 10 to 30%. However, increasing the density of large native trees had a mostly neutral effect. At the species-specific level, the majority of native species responded strongly and positively to increasing understorey volume and native vegetation, whereas exotic bird species had a neutral response.
The probability of occupancy of most species examined was substantially reduced in urban green spaces with little understorey vegetation and few native plants, irrespective of the density of large native trees. Our findings provide evidence that increasing understorey cover and native plantings in urban green spaces can improve biodiversity outcomes. Redressing the dominance of simplified and exotic vegetation present in urban landscapes by designing green spaces with so that some areas have high understorey vegetation volume and a high percentage of native vegetation will benefit a broad array of biodiversity.