Spatio-temporal patterns of tree-growth response to climatic change

Abstract

<p>Trees growing under temperate climate conditions are affected by numerous growth influences. Dendroclimatological analyses of tree-ring chronologies in which the long-term growth/climate relations are investigated, help to assess tree-growth response to climatic controls. The aim of this study was to improve the understanding of spatio-temporal patterns of tree-growth response to climatic change in Central European temperate forests to contribute to a profound assessment of i) the suitability of temperate tree growth as proxy for climate reconstructions and ii) the impact of recent climatic change on temperate tree growth.<br /> A new regional-scale tree-ring network consisting of 48 oak (Quercus spp.), 15 beech (Fagus sylvatica), and three pine (Pinus sylvestris) sites was established in Central-West Germany to investigate spatio-temporal growth/climate relation patterns. New insights in complex growth controls were provided by using methodological approaches not commonly used in temperate forest tree-ring analyses. Climate/growth relations were investigated using correlation analysis, redundancy analysis, and moving correlation analysis. Comparing tree growth with temperature, precipitation, vapor pressure, cloud-cover, and drought index, climate influences over the 20th century were determined. <br /> Drought was found to be the most important growth influencing factor, as quantified by three climate parameters PDSI, precipitation, and vapor pressure. Species-specific investigations illustrate that Fagus sylvatica shows the strongest climate sensitivity, whereas Quercus petraea is most drought tolerant, followed by Quercus robur and Pinus sylvestris. Furthermore, this thesis provides new information about differences in seasonal species-specific climate response patterns. While growth of Quercus petraea is characterized by a short period of summer sensitivity, annual ring formation of the other species is significantly influenced by climate conditions of previous year and growth year periods.<br /> Temporal stability analyses of this thesis illustrated that the relations between tree growth and climate parameters vary over time. Overall, drought sensitivity increased over the last decades of the 20th century. Furthermore, a period of area-wide loss of sensitivity to PDSI and precipitation in the 1940s was detected.<br /> In conclusion, comprehensive methodological approaches and several climate parameters improves the understanding of spatio-temporal patterns of growth/climate responses in temperate forests. By analyzing the strength and temporal variability of growth/climate relations, the accomplishment of suitable climate reconstructions based on temperate tree-ring proxies is estimated to be complicated. Furthermore, the impact of recent climatic change will likely continuously change temperate into more extreme growth conditions in the Central-West German research area, thus potentially leading to changes in forest composition.</p>