Analysis of Differences in the Choice of the Economic Value of Urban Trees in Madrid When Displayed in Situ and in Photographs

Abstract

The determination of an asset’s economic value has always been an important step in improving its management. The Madrid Region legislated the application of the first version of the Norma Granada as a method of appraising ornamental trees. However, the trees in the city of Madrid are only assessed in terms of ecosystem services (i-Tree Eco). A photograph of the asset to be appraised is often used in studies on the valuation of publicly-owned socio-environmental assets such as trees or landscapes. As a tree’s value is very closely linked to its size and to a number of features that can be seen through direct observation of the specimen, it is important to verify the validity of photographs as a method for obtaining the public’s opinion. This work presents a comparison between the valuations chosen by members of the public when observing the tree in situ and in a photograph. The aim is to verify the validity of photographs for their application to a larger sample and to understand qualitatively how citizens assess the trees in a city. The following appraisal methods were used: the American method, Council of Tree Landscape Appraisers (CTLA), Norma Granada and the Burnley method. The survey consisted of ten specimens from ten different species, and ten surveys were taken for each stem, making a total of 100 for each tree species and 1000 surveys in all. The surveys were done randomly and individually. Each interviewed chose one of the three values they were shown when observing the specimen in the photograph and in situ; 84% of the 1000 surveys gave as a result the same value choice when looking at the specimen on site and seeing it in a photograph.