Spatial and temporal variability of stable oxygen isotopes in wood of pine trees on Corsica as indicators of current and past hydroclimate
Final Report Abstract
The project is part of the DFG Research Program „CorsicArchive: Altitudinal Gradients and Forest Response: Climate, Hydrology and Isotope Variability of a Mediterranean Ecosystem“. It aimed at enhancing the understanding of the physiological control and the environmental forcing of short-term oxygen isotope variability in tree rings from two pine species (Pinus nigra and Pinus pinaster) along two elevation gradients (5-1600 m asl) from the Mediterranean coast to the high mountain zone on the island of Corsica. Oxygen isotope values of different hydrological and biological sample material (tree-ring cellulose, needle water, xylem water, precipitation, creek water, soil water) were measured over three consecutive years (2017-2019) in order to (1) quantify the isotope fractionation factors during the various fractionation steps between water uptake and cellulose synthesis, (2) identify the water sources used by the trees, and (3) determine how the isotope signature of underground water and precipitation is reflected in the tree ring. Before focussing on the years 2017-2019, intra-annual oxygen isotope patterns of tree-ring cellulose were examined over several years and correlated with climate parameters. The pattern reflecting dry- warm conditions during summer occurred more frequently after 2007, confirming the trend towards pronounced drought stress in summer. The two pine species studied have developed several adaptation strategies to deal with the Mediterranean precipitation regime, including a bimodal growth pattern, the use of deeper water sources, and the capability to take up water quickly in case of moisture availability. As a result, water sources vary throughout the growing season, ranging from winter snow meltwater to summer precipitation at higher sites and deep soil water reservoirs at coastal sites. The oxygen isotope signatures of underground water and precipitation are imprinted in the tree ring with a temporal offset, varying with elevation and season. Accordingly, isotope fractionation factors during the different fractionation steps between water uptake and cellulose synthesis are also highly variable depending on site and climate conditions during the vegetation period. The results lead to a better understanding of oxygen isotope fractionation in trees on an intra-annual basis, which in turn provides explanations for the long-term variability of oxygen isotopes in tree rings. In a broader sense, the project contributes to a better understanding and quantification of palaeoclimate in the western Mediterranean, which is a necessary prerequisite for understanding current and future climate change in this climatic sensitive region.
Publications
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(2018): Long-term oxygen isotope chronologies from a Mediterranean island. TRACE-Volume, 16, 46-53
Szymczak, S., Bräuning, A., Joachimski, M.
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(2019): Growth variability of two native pine species on Corsica as a function of elevation. Dendrochronologia, 54, 49-55
Häusser, M., Szymczak, S., Garel, E., Santoni, S., Huneau, F., Bräuning, A.
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(2019): The relationship between climate and the intra-annual oxygen isotope patterns from pine trees: a case study along an elevation gradient on Corsica, France. Annals of Forest Science, 76, 1-14
Szymczak, S., Bräuning, A., Häusser, M., Garel, E., Huneau, F., Santoni, S.
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(2020): A dendroecological fire history for central Corsica/France. Tree-Ring Research, 76(1), 40-53
Szymczak, S., Bräuning, A., Häusser, M., Garel, E., Huneau, F., Santoni, S.
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(2020): How Do Mediterranean Pine Trees Respond to Drought and Precipitation Events along an Elevation Gradient? Forests, 11, 758
Szymczak, S., Häusser, M., Garel, E., Santoni, S., Huneau, F., Knerr, I., Trachte, K., Bendix, J.,Bräuning, A.
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(2020): Temporal offset between precipitation and water uptake of Mediterranean pine trees varies with elevation and season. Science of the Total Environment, 755, 142539
Juhlke, T.R., van Geldern, R., Barth, J.A.C., Bendix, J., Bräuning, A., Garel, E., Häusser, M., Huneau, F., Knerr, I., Santoni, S., Szymczak, S., Trachte, K.
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(2020): Tracking the oxygen isotope signature from source to sink in pine trees along an elevational gradient in a Mediterranean ecosystem. Chemical Geology, 549, 119695
Szymczak, S., Barth, J., Bendix, J., Huneau, F., Garel, E., Häusser, M., Juhlke, T., Knerr, I., Santoni, S., Trachte, K., van Geldern, R., Bräuning, A.
