The value of green walls to urban biodiversity

Despite increased interest in the implementation of green walls in urban areas and the recognised benefits of monetary valuation of ecosystem services, no studies have been undertaken to estimate the economic value of biodiversity they provide. The valuation of natural resources allows policy makers to justify resource allocation. Using the Southampton, UK, as a case study, this paper estimates the public's perceived value of green walls to urban biodiversity, in the form of their willingness to pay (WTP). Estimates were derived using a random parameter model that accounted for socio-economic and attitudinal determinants of choice, using choice experiment data. Three green infrastructure policies were tested; two green wall designs ('living wall' and 'green façade') and an 'alternative green policy'; and compared against 'no green policy'. Results indicated a WTP associated with green infrastructure that increases biodiversity. Attitudinal characteristics such as knowledge of biodiversity and aesthetic opinion were significant, providing an indication of identifiable preferences between green policies and green wall designs. A higher level of utility was associated with the living wall, followed by the green façade. In both cases, the value of the green wall policies exceeds the estimated investment cost; so our results suggest that implementation would provide net economic benefits.