Patch, matrix or corridor? Estimating the role of urban gardens for green infrastructure in Braunschweig, Germany.

METAPOLIS is the network of large, medium and small municipalities in a rural matrix, linked by flows of traffic, data, goods and services. Together with stakeholders, an interdisciplinary team of scientists from the Technische Universität Braunschweig and the Leibniz Universität Hannover studies the networks that shape rural-urban relationships in Lower Saxony, Germany, with the aim of making these relationships more sustainable (METAPOLIS project).
Green Infrastructure (GI) is a key component of the METAPOLIS, providing ecosystem services, habitat and habitat connectivity. Gardens make up a large proportion of GI [1] and can provide a range of ecosystem services [2]. Depending on size, structure, management, and location, they can also be quite species-rich [3]. Understanding the role of gardens as a component of GI is not straightforward, though. They are mostly privately owned and individually managed, which means that public data on their extent and structure is often missing. In addition, the pressure on garden land in many cities is quite high, because urban growth is to be achieved through densification rather than expansion. This is also the case in Braunschweig, Germany, the biggest city in our METAPOLIS study area.
To increase our knowledge of the role of gardens for GI, in particular their role for habitat and habitat connectivity, we followed a two-step approach. (i) We combined high resolution LiDAR, remote sensing, and GIS data to estimate 3D vegetation structure and fragmentation. (ii) We then estimated connectivity of gardens with surrounding habitat patches, based on the 3D vegetation structure, using a circuit theory approach (Circuitscape) [4]. Our results help with including gardens into GI planning by highlighting (a) which gardens should be prioritized for protection from development and (b) which gardens could be targeted for enhancement, e.g., through funding schemes.