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The GrüneLunge project is based on the knowledge that green spaces, and trees in particular, are extremely important for the microclimate and air quality in the city. Improving urban microclimate and air quality is one of the most important regulating ecosystem services provided by urban trees. Conversely, urban trees are often stressed by urban conditions, which reduce their beneficial effects.
Therefore, in the first phase of the project, information was collected characterizing the climate on the one hand and tree characteristics in the city on the other hand. The data collected by KIT-ITAS from GrüneLunge 1.0 were used to quantify the regulating ecosystem services of urban forests. For this purpose, the United States Forest Service's i-tree-eco urban ecosystem services modeling software was used. It provided us with some estimates of the potential regulating ecosystem services of urban trees. However, it was not entirely accurate because many equations used in the i-tree-eco software to model regulating ecosystem services were generalized and not tailored to the urban site conditions in Karlsruhe and Rheinstetten. In a parallel project to GrüneLunge, KIT-IMK developed a process-oriented model (Tree4C) for estimating the regulating ecosystem services of individual urban trees.
Based on the data collected by GrüneLunge 1.0, we will use the Tree4C model to quantify the effects of urban trees on ambient temperature and air pollution in the cities of Karlsruhe and Rheinstetten. The dependence of these effects on weather and water availability will be explicitly considered, and their conservation will be investigated with respect to sensitivity and climate scenarios. Based on this, the potential influence of urban management through maintenance, irrigation, and species selection will be elaborated. To achieve this goal, the Tree4C model will be used to represent the environmental impacts of trees as a function of dimension, location, and tree species-specific sensitivity to drought stress. This model will be parameterized and initialized for significant urban trees and their locations based on the Karlsruhe urban tree cadastre and additional measurements from both project phases. Further investigation results, such as the determination of temperature differences in the vicinity of green spaces, will be used to evaluate the modeling. The subproject thus builds on previous work and goes beyond specific measurement locations and times to analyze the effects of different, but expected future, extreme weather events (heat waves) and possibilities for countermeasures (irrigation).
Point-based system and exchange of ecosystem services
In Germany, major infrastructure projects such as airports, housing estates, industrial areas or soccer stadiums and entertainment venues are increasingly being relocated to peri-urban areas, as cities are already heavily sealed and densified. Forests in the urban fringe, in particular, therefore provide many important ecosystem services for urban residents, in addition to trees in the city. For example, during the COVID-19 pandemic, people from Karlsruhe also used forests near the city in Rheinstetten for recreation and to relieve stress. Providing and regulating ecosystem services such as improving air quality also have a transboundary effect between urban and peri-urban areas. However, the expansion of urbanization contributes to the fact that areas close to cities are also increasingly densified and sealed. Thus, trees and forests close to cities are coming under increasing pressure.
In the GrüneLunge project, we therefore hypothesized that the administrative and practical management of urban trees and forests must also transcend the boundaries between urban and suburban areas. Proactive, cross-zonal, and holistic planning and management is needed to strengthen the region's overall resilience to drought disasters, heat waves, and floods. In GrüneLunge 1.0, we proposed that part of transboundary management of urban and peri-urban regions could be the creation of a standardized, point-based assessment system and the development of an approach to ecosystem service exchange between urban and peri-urban areas.
The GrüneLunge 1.0 project outlined a concept for exchanging ecosystem services of trees and forests between urban and peri-urban regions. The concept is based on a scoring system to operationalize and assess ecosystem services based on field data collected during GrüneLunge 1.0. In the future, the approach will enable the cross-regional compensation of ecosystem services on an ecological and cultural level.
The goal of the GrüneLunge 2.0 project is to further develop the ecosystem service point system and to create a legal framework for the concept. Furthermore, possibilities of the compensation concept of ecosystem services are discussed, which can be applied exemplarily between Karlsruhe and Rheinstetten and perspectively for other municipalities close to the city.