Effects of different land-use planning instruments on urban shrub and tree canopy cover in Zurich, Switzerland

Sustainable urban development requires not only dense and land-saving construction, but also a large share of urban vegetation. A planned unit development (PUD) is a land-use planning instrument that is often used to improve urban quality in urban renewal and densification worldwide. In this study, we analyse the influence of PUDs on urban vegetation in the Canton of Zurich, Switzerland, by contrasting them with conventional zoning. We modelled the share of shrub and tree canopy cover per neighbourhood block using generalized linear mixed effect models (GLMM), with the type of planning instrument as the focal predictor amongst other control variables known from the literature to be influential on urban vegetation. Results show that PUDs are associated with significantly less urban vegetation cover than conventional zoning. This is unexpected and raises concerns. Given how important PUDs are as levers for improving urban quality, their observed inability to promote valuable shrub and tree structures leads us to recommend that good landscape planning and long-term management of (existing and new) urban vegetation be included as an additional standard criterion of high priority in the assessment of future PUDs.