Identification of most valuable trees based on both ecosystem services they provide and their actual usage by residents in the Racibórz case study

Increased urbanization has made the monitoring of trees outside of forests extremely important. Gains and losses of green spaces in cities are assessed (Nowak & Greenfield, 2020), and attempts are made to determine their benefits (Davies et al., 2017) and estimate them (Zięba-Kulawik et al., 2021). However, identifying the most valuable trees is still a challenge for two reasons. First, trees provide many different benefits, such as oxygen, shade, food, and others. They are animals' habitats; they also contribute to the aesthetics of urban spaces, create recreational spaces, and many more. Each of these ecosystem services (ES) is expressed by different measures, and we cannot directly compare them. Secondly, trees that are objectively valuable in terms of different ES will not necessarily be valued by their potential beneficiaries. Urban residents often value more small and relatively insignificant trees which are more accessible to them, than old and big ones. Thus, mapping urban trees' value needs to consider the range of different ES and the residents' opinions of their importance in their daily lives. We address this challenge using multi-criteria analysis, fuzzy set theory, and Analytical Hierarchy Process to identify the most valuable trees in Racibórz (Poland). In this study, three data sources were used to identify valuable trees:
1. LiDAR data enabled the location of trees and estimation with i-Tree Eco model of some ES they provide (air purification, sun protection, oxygen provision, and regulation of air humidity and soil moisture),
2. Expert mapping gives us information about other ES related to those trees (such as providing animal habitat, food, or place of recreation) and,
3. A survey with an interactive map (geo-questionnaire) was used in order to identify trees valuable to residents in their daily lives.
Following Kronenberg (2012), 17 ES representing four classes of services: provisioning, regulating, habitat, and cultural ones, were included considering their relative importance (Przewoźna et al. 2022). The results identify the most valuable trees considering all ES they provide and their actual use by residents determining their effective availability. They also highlight valuable green spaces inaccessible to most residents. The approach we used can be applied to tree management at the local level to identify areas in need of special protection, allowing access to the benefits provided by trees to residents.