Response of Growth to Climate within Oaks of the World Heritage Site of Prussian Gardens

Abstract

Trees constitute the basis for structure and convey the particular impression of most historic gardens and parks. In the World Heritage property 'Palaces and Parks of Potsdam and Berlin' (Germany) oaks are among the most abundant tree species and can be seen as key species. Questions about exact age, extent and time of environmental influences and impact of extreme weather events still remain unanswered. Against this background, this study tries to get answers about the reaction of these oaks to climatic conditions at three sites, and about the link between vitality and tree-ring growth with a dendrochronological approach. A correlation analyzes and moving correlations gave insight in climate-growth relationships and their stability. Growth reactions were also evaluated in single years by pointer year analyses and superposed epoch analyses (SEA).The oak trees show declining growth trends which can be interpreted as typical sign of the old stage of trees and that are not necessarily linked to changing climatic conditions. However, our results highlight the significance of adequate precipitation sums in previous year's July and September and from current May to July for xylogenesis. This result is confirmed by the correlation analyzes to ground-water table and a drought index as well as by the pointer year analyses and the SEA. The climate-growth correlations show instability in many months of previous and current year over recent decades. The results of the present study show strong site-specific drought sensitivity for Quercusthat is strongly correlated with soil moisture conditions and precipitation.

Using the dendro-climatological signal of urban trees as a measure of urbanization and urban heat island

“…This combination of correlations was found for tree-ring widths of deciduous trees, in particular beech, oak and ash, but less so for lime. In addition, the combined summer signal translated into a strong correlation with the aridity index, dMI, similar to results obtained by Gillner et al (2020) for oak in Potsdam. However, the strongest correlations of tree-ring width and climate was found with monthly averaged diurnal temperature range, MTR.…”

“…It might be physiologically explained by the hypothesis that more warm days towards the end of winter, when the needles are not frozen anymore, result in an earlier shift towards a more positive carbon balance in the pines (Havranek and Tranquillini 1995). The summer signal of deciduous forests trees, especially oaks, has commonly been found in western (Friedrichs et al 2009a, b) and eastern Germany (Bonn 1998;Gillner et al 2014Gillner et al , 2020, in France (Lebourgeois et al 2005), Czech Republic (Dobrovolný et al 2016), and Sweden (Drobyshev et al 2008). Scharnweber et al (2011) identified a clearly increasing West-East gradient for the negative temperature signal in beech.…”

“…Liebl. and Q. robur L.) and beech (Fagus sylvatica L.) show negative relationships with air temperature and positive relationships with precipitation during the summer months, which has been interpreted as drought response (Friedrichs et al 2009a;Scharnweber et al 2011;Fischer and Neuwirth 2013;Gillner et al 2020). Cook et al (2015) identified increasing drought stress for the leading tree species beech, oak, and pine (Pinus sylvestris L.) in Central European forests.…”