Abstract
Using dendroclimatological techniques this study investigates whether inner city tree-ring width (TRW) chronologies from eight tree species (ash, beech, fir, larch, lime, sessile and pedunculate oak, and pine) are suitable to examine the urban heat island of Berlin, Germany. Climate-growth relationships were analyzed for 18 sites along a gradient of increasing urbanization covering Berlin and surrounding rural areas. As a proxy for defining urban heat island intensities at each site, we applied urbanization parameters such as building fraction, impervious surfaces, and green areas. The response of TRW to monthly and seasonal air temperature, precipitation, aridity, and daily air-temperature ranges were used to identify climate-growth relationships. Trees from urban sites were found to be more sensitive to climate compared to trees in the surrounding hinterland. Ring width of the deciduous species, especially ash, beech, and oak, showed a high sensitivity to summer heat and drought at urban locations (summer signal), whereas conifer species were found suitable for the analysis of the urban heat island in late winter and early spring (winter signal).The summer and winter signals were strongest in tree-ring chronologies when the urban heat island intensities were based on an area of about 200 m to 3000 m centered over the tree locations, and thus reflect the urban climate at the scale of city quarters. For the summer signal, the sensitivity of deciduous tree species to climate increased with urbanity.These results indicate that urban trees can be used for climate response analyses and open new pathways to trace the evolution of urban climate change and more specifically the urban heat island, both in time and space.
Highlights
The climate influenced locally by city structures is usually summarized under the term ‘urban climate’ (Matzarakis 2001; Oke et al 2017)
Regardless of species, site chronologies of radial growth (Fig. 4A) demonstrated a common long-term growth trend characterized by decreasing ring-widths since the late 1960 onwards
Correlation coefficients for the same tree sites with the four weather stations varied minimally and insignificantly. This finding is consistent with the notion that the regional climate is fairly homogenous outside the urban areas, and that climategrowth relations overall are relatively consistent across northeastern Germany and surrounding lowlands (Balanzategui et al 2018; Scharnweber et al 2019; Harvey et al 2020)
Summary
The climate influenced locally by city structures is usually summarized under the term ‘urban climate’ (Matzarakis 2001; Oke et al 2017). Different forms of land use within cities cause a variety of micro- and local climates (Kuttler 2004). The urban heat island (UHI) is one of the most important characteristics of urban climates (Arnfield 2003). UHI describes the phenomenon whereby urban areas typically exhibit higher air temperatures than surrounding sub-urban and rural areas, and was first recognized in the early 1800s (Howard 1833). Diurnal cycles of air temperature are different from those in the surrounding area (Oke 1982). Nighttime minimum air temperatures are much higher (Matzarakis 2001; Kuttler et al 2015). ‘Trees are wonderful things’ (McCarroll and Loader 2004) because they cool the environment (Smithers et al 2018), and because they deliver important ecosystem services
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