Making the case for gardens: Estimating the contribution of urban gardens to habitat provision and connectivity based on hedgehogs (Erinaceus europaeus)

Abstract

Preserving and expanding green infrastructure (GI) is key to biodiversity conservation in cities, but a significant share of urban land is commonly underutilized in GI plans: gardens. This is despite the fact that gardens can support diverse wildlife communities by providing habitat and by functioning as corridors. In this article, we apply circuit theory-based modeling in order to quantify the contribution of two types of gardens to connectivity in the city of Braunschweig, Germany: private gardens and allotment gardens. We ran four permeability scenarios: 1.) all green spaces including private and allotment gardens are permeable; 2.) private gardens are non-permeable; 3.) allotment gardens are non-permeable; 4.) only public green spaces but no gardens are permeable. We based our modeling on the European hedgehog (Erinaceuseuropaeus), a common, relatively well-understood and well-liked urban species. Observations by citizen scientists were used for a plausibility analysis and interpreting the results. Our results confirm the importance of gardens for providing habitat and connectivity. The overall landscape permeability to the movement of hedgehogs would decrease by 75% and the area of core habitats would decline by 63% without private and allotment gardens. While private gardens contribute most to landscape connectivity, some allotment gardens occupy key areas for the overall connectivity in the city. In conclusion, circuit theory-based modeling is a promising tool for urban GI planning and the output of those models can inform decision makers and gardeners.