Ecosystem services of urban forests

Improving the modeling of regulating ecosystem services of urban trees

 

The GrüneLunge project is based on the recognition 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 reduces 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 WP1 of 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 general 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 (from work packages 1, 2, and 3) 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 valuation system and exchange of ecosystem services

 

In Germany, major infrastructure projects such as airports, housing developments, industrial areas or soccer stadiums and entertainment venues are increasingly being relocated to peri-urban areas, as cities are already heavily sealed and densified. This expansion of urbanization contributes to the fact that peri-urban areas are increasingly densified and sealed. Both urban and peri-urban trees and forests are associated with ecosystem services and cannot be considered in isolation. This is because urban and peri-urban residents commute between regions not only for work reasons, but also to visit green spaces, nature reserves, forests, etc. for recreation and cultural reasons. For example, during the COVID-19 pandemic, people from Karlsruhe and Rheinstetten increasingly visited urban and peri-urban forests within their city limits and also traveled beyond city limits to relieve stress. Supportive ecosystem services such as microhabitat structures in urban trees help not only bats and birds from inner cities, but also from areas near cities. Providing and regulating ecosystem services benefit air quality, climate change adaptation, and mitigation, which have transboundary effects between urban and peri-urban areas.

 

For these reasons, the administrative and practical management of these areas must also transcend the urban/peri-urban boundary. 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 developed a concept for exchanging ecosystem services of trees and forests between urban and peri-urban regions. The concept is based on a scoring system for operationalizing and valuing ecosystem services based on field data collected during GrüneLunge 1.0. The approach allows for cross-regional compensation of ecosystem services at the ecological and cultural levels.

 

The compensation concept outlined here is a holistic approach that incorporates the regulating, provisioning, supporting, and cultural ecosystem services of forests and green spaces and focuses on urban and peri-urban spaces. The original impetus for the development of the compensation concept was the existing Ecological Account Ordinance (LUBW 2010). This offers the possibility of implementing measures to improve the natural balance in advance of interventions in nature and landscape, which demonstrably provide added value for the protected goods habitats, soil and water. The measures must be assigned to one of six impact areas. These impact areas focus, for example, on the improvement of biotopes, soil functions and the promotion of certain species. Since the ecosystem services of urban trees and the assessment of cultural ecosystem services have not been considered in the eco-account regulation so far, the project is an important addition for the management of urban green spaces.

 

The aim is the further development and piloting of a compensation concept of ecosystem services, which can be applied exemplarily between Karlsruhe and Rheinstetten and in perspective also for other municipalities close to the city. The concept is based on the preliminary work described above, which incorporates and operationalizes the regulating, supporting, providing and cultural ecosystem services with the help of a point system.