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Inter- and transdisciplinary approaches to develop strategies for increasing the resilience of trees in growing cities and urban regions (GreenLung) [Inter- und transdisziplinäre Entwicklung von Strategien zur Erhöhung der Resilienz von Bäumen in wachsenden Städten und urbanen Regionen (GrüneLunge)]
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Increasing urbanization, climate change, and plant disease pose accumulative threats to city and community-owned forests (CCF). This requires the forest to adapt to new climatic conditions to continuously provide essential recreational functions for the urban population in the future. The COVID-19 pandemic increased the demand for CCF as a place to meet, play sports, and relax. However, our knowledge of challenges in combining climate change adaptation and the increased number of visits and demand for recreation in CCF management is yet limited. In this study, we, for the first time, interviewed 16 stakeholders from different backgrounds about their opinions on climate change adaptation (CCA) of CCF, its importance as a recreational space, and conflicts between the two fields of action that occurred during the COVID-19 pandemic. It is expected that comparing perspectives from different stakeholder groups can lead to improved reflection and strengthen the sustainable management of the CCF through knowledge-based and participative decision-making. Using semi-structured interviews and qualitative data analytics with MAXQDA software, we found that stakeholders particularly highlighted the importance of the recreational function of the CCF during the pandemic. At the same time, the behavior of visitors was criticized. We identified that functional conflicts between the need for relaxation and essential functions for CCA of the CCF have increased during the pandemic. These include other biodiversity and protective functions. The interviewees, therefore, suggested enhancing the local population's communication and education. Further, the possibility of increased visitor guidance has been discussed. It has been identified that more research and location-adjusted planning are needed to evaluate the use of non-native species for the urban forest’s climate change adaptation.
Trees in cities provide multiple ecosystem services. However, simultaneously ensuring healthy trees with high habitat diversity can be challenging in a harsh urban environment. We compared health, microhabitats, and bat activities between native ( Quercus robur L.) and non-native ( Quercus rubra L.) oaks growing in different urban habitats (street vs. park) in Karlsruhe, southwestern Germany. We randomly selected 167 oak trees with a diameter at breast height (DBH) greater than 20 cm across the city from Urban Tree Registrar. We performed tree health assessment, dendrometric, and microhabitat inventory. We recorded the bat activities for four days on 45 native and non-native oaks with acoustic loggers installed on the trees. We found that non-native oaks were healthier than native oaks but provided less abundance and richness of microhabitats. Tree size (positive effect) and pruning (negative effect) strongly influence microhabitat richness and abundance. In addition, park trees hosted significantly more microhabitats than street trees. We recorded the activities of 9 bat species from 4 genera. Pipistrellus bats were more active in park trees than street trees. Long-eared bats ( Plecotus ) were more active near the native than non-native oaks. Bats are likely favored by microhabitats such as fork split, lightning scar, and woodpecker "flute" that are more common in less healthy trees. We conclude that non-native red oak can be planted alongside streets, where the conditions are harsher than in parks, to better adapt to climatic changes and stay healthy with less maintenance. The preservation of native pedunculate oak trees, especially within parks, is paramount for urban biodiversity conservation because of their potential to provide microhabitats and supporting bats.
Key Message
In an urban area, resistance and resilience of stem diameter growth differ substantially between tree species. Traffic emissions are reflected in wood nitrogen isotopes, but do not affect drought tolerance.
Abstract
With increasing drought and heat, the benefits of urban trees such as shading and cooling become more important. Yet, it is necessary to identify tree species able to withstand such extreme climatic conditions. We studied the resistance and resilience of stem diameter growth of five deciduous tree species in an urban area in Southwest Germany to three exceptional drought periods (2003, 2011 and 2015) for differences between and within species, especially considering the intensity of traffic emissions (NO x ). Analyses of the stable isotopic composition of carbon (δ ¹³ C) and oxygen (δ ¹⁸ O) as well as the intrinsic water-use efficiency (WUE i ) in the tree rings were carried out. Further, we investigated the stable isotopic composition of nitrogen in the wood (δ ¹⁵ N) to assess its potential as an indicator of NO x emissions from traffic. Stem diameter growth in all species was strongly limited by low water availability in spring, as was also reflected in elevated δ ¹³ C and δ ¹⁸ O values in Acer platanoides and Tilia cordata , which were particularly sensitive to drought. In contrast, growth of Platanus × hispanica and Quercus robur was less affected by drought, and resistance of Carpinus betulus ranged in between. Across species, δ ¹⁵ N was higher in trees located closer to roads and exposed to higher NO x traffic emissions. Unexpectedly, these conditions did not significantly affect drought resistance/resilience. Our study demonstrates the potential and interpretative challenges of coupled dendroecological and isotope analyses. It also indicates clear species-specific differences in drought tolerance and thus helps to identify suitable urban tree species.
Reducing trade-offs among ecosystem services (ES) from urban and peri-urban forests (UPF) is crucial for human wellbeing. We performed spatial analyses and quantified the supply and trade-offs between 23 ES (grouped into three categories: provisioning, regulating, and supporting) from UPF in the Karlsruhe region, southwest Germany. The supply of ES was calculated, normalized, and mapped from field data collected at 201 randomly selected plots in UPF, located in agricultural land, built-up areas (i.e., artificial surfaces), and forest and seminatural areas. Trade-offs were calculated as the root mean squared error between the benefits from two categories of ES. Predominantly, there was a synergy between provisioning and regulating ES; however, trade-offs with supporting ecosystem services were detected in all three land-uses. The UPF areas with a high supply of supporting ES (e.g. tree species, structural and tree microhabitat diversity) had a lower supply of regulating and provisioning ES, resulting in trade-offs. This study demonstrates trade-off patterns between the ES in UPF, which should be considered in the management of UPF and sustainable city design. Current UPF should be transformed to a more multifunctional and climate-resilient state to guarantee ES and human wellbeing in cities.
Differences in the accessibility to urban resources between different racial and socioeconomic groups have exerted pressure on effective planning and management for sustainable city development. However, few studies have examined the multiple factors that may influence the mitigation of urban green spaces (UGS) inequity. This study reports the results of a systematic mapping of access inequity research through correspondence analysis (CA) to reveal critical trends, knowledge gaps, and clusters based on a sample of 49 empirical studies screened from 563 selected papers. Our findings suggest that although the scale of cities with UGS access inequity varies between countries, large cities (more than 1,000,000 population), especially in low- and middle-income countries (LMICs), are particularly affected. Moreover, the number of cities in which high socioeconomic status (high-SES) groups (e.g., young, rich, or employed) are at an advantage concerning access to UGS is substantially higher than the number of cities showing better accessibility for low-SES groups. Across the reviewed papers, analyses on mitigating interventions are sparse, and among the few studies that touch upon this, we found different central issues in local mitigating strategies between high-income countries (HICs) and LMICs. An explanatory framework is offered, explaining the interaction between UGS access inequity and local mitigating measures.
In the times of enlarging cities and more people living in cities, it is essential to maintain the quality of life for everyone. Urban forests make a significant contribution to this. In urban areas, productive ecosystems are essential to maintain human health and well-being. However, problems like increasing urbanization, changing climate, and pollution in the air, water, and soil can endanger urban ecosystems like urban forests. Having or building resilient urban forests is seen as a possibility to maintain ecosystem services provided by urban forests. Under future conditions, they may become essential for human life in urban areas as some are critical for human health. This study is a literature review of past research dealing with resilience in urban forests. Forty-one articles published in the years 2006 to 2019 that complied with the search criteria were reviewed. Results show that only three articles used a definition of the resilience of urban trees after disturbance based on a formula; two articles used a definition of resilience based on natural ecosystems. The remaining articles did not define resilience while using the term in the articles.Out of the reviewed articles, four major themes were identified: urban forest management, urban biodiversity, urban soil, and socio-economic conditions. Nine articles included content about urban soils, 19 articles about urban forest management, 30 articles about urban biodiversity, and 11 articles about socio-economic conditions. As (built) urban forests in cities differ considerably from natural ecosystems, some authors rated monitoring and management actions as necessary, mainly for new establishments and the integration of new species. Authors expressed contradicting opinions on species richness. While some articles suggested focusing on native or endemic species, others proposed to increase species diversity to enhance urban forest resilience. Tolerances and resistances of tree species are essential for urban areas and may gain importance in the future, increasing extreme weather events leading to more frequent pest and disease outbreaks. Results indicated a focus on urban soil quality as a basis for plant growth, and tree health is an essential factor in urban forestry. Municipal authorities need to adapt management actions to create and maintain an urban forest to the benefits they intend to achieve for the city considering local conditions like climate, species pool, and specific resistances. At the end of the review, a framework recommends actions for a structured collaboration of municipal authorities, researchers, and citizens to achieve resilient urban forests.
Cultural ecosystem services (CES) of urban and peri-urban forests (UPF) contribute to the urban population's health and well-being. However, UPF face numerous threats from increasing urbanization and climate change. A comprehensive understanding of the flow of the forests' CES between urban and peri-urban areas was lacking. Further, there is little empirical evidence of how people valued and used UPF during the COVID-19 pandemic. In this study, we assessed residents' perceptions of CES provided by UPF, and their spatial distribution in Karlsruhe and Rheinstetten, Germany, using a participatory map-based questionnaire survey. Respondents (n=501) were asked to indicate five preferred locations of UPF and to rate the individual UPFs’ importance concerning various CES. Heatmaps were created to visualize the results, and normalized ratings of the perceptions were examined. The study demonstrated that residents prefer nearby locations for all studied CES but place a higher value on peri-urban forests regardless of their frequency of use. The survey results show an increase in visits to UPFs during the COVID-19 pandemic. The importance of urban forest for citizens’ stress reduction during the pandemic was highlighted by the participants. We recommend considering these findings in urban forest planning.
Jede*r kann einen Beitrag zu Arten- und Klimaschutz durch Veränderungen im eigenen Garten leisten. Das ist die Idee der Kampagne, die in dem Projekt GrüneLunge konzipiert und in der Stadt Rheinstetten durchgeführt wird. Zu Beginn wurden Bürger*innen mit öffentlichen Veranstaltungen über naturnahe Gartengestaltung informiert. Im Anschluss werden 16 Haushalte bei der Umgestaltung ihrer Gärten über 1 ½ Jahre unterstützt und vernetzt. Schwerpunkte der Kampagne sind, Impulse für mehr Artenschutz in die Stadtgesellschaft zu senden und die Selbstwirksamkeit der Bürger*innen zu fördern. Aus
den Ergebnissen der wissenschaftlichen Begleitforschung soll auch eine Handreichung für andere Kommunen entstehen.