Trees as Indicators of the Urban Heat Island

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The project "Bäume als Indikatoren für die urbane Wärmeinsel (BIWi)" (trees as indicators of the urban heat island) comprises a pilot study for generating and analyzing chronologies of different tree ring parameters (tree-ring width, pointer year catalogs, wood anatomical features). Dendroclimatological methods to acquire data at 12 urban-ecologically different sites in Berlin will be applied. Berlin is the City in Germany with the largest urban heat island (UHI) effect. The objective of the project is to investigate the magnitude of quality and certainty of growth features that can be attributed to UHI effect. Based on established methods of measurement and data processing techniques in dendrochronology and time series analysis such as correlation and regression analysis, principal component analysis and statistics of extreme years a set of methods for urban areas are to be developed. With this approach we aim at determining and prioritizing the growth factors for mean climatic and extreme weather conditions (dry seasons, heat waves, smog) at different sites in a combination of methods. For this purpose, tree-ring chronologies as well as catalogs addressing extreme growth reactions and wood anatomical features (freeze circles, density fluctuations, etc.) will be generated for approx. 150 trees at 12 urban-ecologically different sites. The UHI effects will finally be separated from general climatic growth conditions by comparison with sites from rural sites outside of Berlin. In addition to the analysis of specific urban tree species (plane, maple, littleleaf linden and similar species) the differentiating process particularly also requires the analysis of basic forest tree species such as oak, beech or pine to prevent the identified urban-rural diversities from being blurred by species specific differences. The results achieved by the pilot study will be evaluated and interpreted within two master theses and additionally be published in an internationally established peer-reviewed journal. Current studies use dendroclimatology successfully to analyze the growth of urban trees. The innovation within the BIWi-project is based on the application of urban trees and dendroclimatological techniques for the analysis of urban climatological effects with particular focus on the evolution of the UHI. In case of success, this pilot study will serve for pursuing a subsequent project. Its goal will be the development of a general procedure investigating the spatial distribution and spatio-temporal evolution of UHIs using dendroclimatological data. Perspectively, this can contribute to giving retrospective and projective evidence for the evolution of UHIs in the light of changing climatic, demographic and urban planning developments.