Unveiling urban ecological integrity: spatially explicit assessment in contrasting environments

Although much attention has been paid to improve the representation of the urban spatial complexity, most efforts have been limited to the inclusion of green cover data to describe the biological component of cities, leaving the measurement of crucial urban ecological properties out of the picture. To tackle this, the Urban Ecosystem Integrity Index (UEII) was recently proposed to spatially represent the interplay between the intensity of urbanization and the biological components of cities, including urban biodiversity. The UEII has shown to be effective in measuring the ecosystem integrity of a Neotropical city; however its generalized applicability remains to be tested. Thus, here we tested the suitability of the UEII when applied in a boreal city and also evaluated if it adds more valuable information than the NDVI (also contrasting it with a UEII previously published for a tropical city), which is often suggested as a proxy of urban greenness and therefore the ecology of cities. We calculated the UEII by considering land surface temperature, built-up cover, and native plants and bird species richness of the city of Lahti, Finland (Palearctic; boreal). The UEII showed to be robust, comparable, and effective in capturing the intra and inter-urban spatial heterogeneity of both cities. Moreover, although the UEII and NDVI values correlated, the variance in such correlation showed the detail that the UEII brings to the quantificaiton of the ecological integrity of the cities, representing a more integral indicator. Thus, our findings indicate that the UEII is a valuable tool to inform on areas requiring ecological enhancement, as well as identifying those that are thriving, in cities ranging from tropical and highly biodiverse to boreal and with considerable less biodiversity. We tested the suitability of the UEII in a boreal city, contrasting it with that of a tropical one.The index effectively captures the spatial heterogeneity of the city.The UEII allows to identify the diverse ecosystem integrity scenarios of cities.It provides a broader ecological representation of cities than the NDVI.The UEII represents a quantitative and spatially explicit tool for spatial planning.