Minimising the ecological impact of urban growth

Background/Question/Methods

Urbanisation causes severe environmental degradation and continues to increase in scale and intensity around the world, but little is known about how we should design cities to minimise their ecological impact. For a given human population size, a sprawling style of development requires greater conversion of natural habitat than higher density development, and so the overall ecological impact of sprawling growth might be greater despite its lower intensity. We compare the consequences of compact and sprawling urban growth patterns on bird distributions across the city of Brisbane, a biodiverse, subtropical city on Australia’s east coast. Based on urban growth targets, we simulated the addition of 84,642 houses to the city by 2031, under two simple scenarios reflecting (i) compact growth where new dwellings are accommodated by increasing the density of existing residential areas, and (ii) sprawling growth where new dwellings are placed in green spaces usable for urban growth. We measure the impacts of these alternate urban growth patterns on bird distributions by (i) modelling future changes in area of occupancy of bird species under each scenario, (ii) quantifying the magnitude of expected local extinctions, and (iii) determining the consequences for human proximity to green spaces. 

Results/Conclusions

We discovered that urban growth of any type reduced the mean predicted area of occupancy across bird species, but that compact development substantially slowed these reductions at the city scale, resulting in fewer local extinctions. Urban-sensitive species particularly benefitted from compact development at the city scale because large green spaces were left intact, while the distributions of non-native species expanded as a result of low density development. Our results suggest that limiting the spatial expansion of urbanisation with high density development will minimise ecological disruption at regional scales, at least in cases where existing green spaces are ecologically intact. However, higher density residential areas typically result in smaller backyards which may limit opportunities for people to experience nature close to home. Ultimately, a compact form of development might generate a spatially-mediated trade-off between regional biodiversity conservation and local human experiences of nature.