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Langlebige Bäume können langfristige Klimaänderungen, aber auch kurzfristige Witterungsextreme in Form ihres Zuwachses und ihrer holzanatomischen Struktur archivieren. Die Variationen der Jahrringbreite und anderer Holzparameter reagieren dabei art- und standortsspezifisch auf unterschiedliche Klimafaktoren. An kalt-humiden Gebirgsstandorten ist die Jahrringbreite oft mit den Temperaturen der Wintermonate vor der Wachstumsphase oder mit der mittleren Temperatur über die Vegetationsperiode korreliert, während an semiariden Gebirgsstandorten der Zuwachs eher durch die verfügbare Feuchtigkeit während der Wachstumsperiode limitiert wird. Die maximale Spätholzdichte ist ein guter Indikator für die Sommertemperatur, während Isotopenverhältnisse des Sauerstoffs und des Kohlenstoffs in der Zellulose des Holzes sensitiv auf hydroklimatische Klimaparameter und Verdunstung reagieren. Quantitative Analysen der holzanatomischen Struktur ermöglichen eine extrem hohe zeitliche Auflösung der gespeicherten Klimainformation bis auf wenige Tage. Durch Kombinationen mehrerer Holzparameter mit unterschiedlicher saisonaler Sensitivität kann eine umfassende Rekonstruktion des Klimageschehens im Jahreslauf durchgeführt werden. Somit können Jahrringdaten auch mit anderen Klimaproxies wie Eisbohrkernen, Seesedimenten oder Abflussdaten verglichen werden, bieten dabei aber eine exakte, jahrgenaue Datierung. Im Hochgebirge bieten sich dadurch Möglichkeiten, landschaftsdynamische Prozesse wie Gletscherschwankungen und geomorphologische Ereignisse anhand von Jahrringdaten zu analysieren. Mit Hilfe langlebiger Straucharten können Jahrringanalysen auch in die alpine Region jenseits der Baumgrenze ausgeweitet werden. Which environmental factors can be analyzed using tree rings? Long-living trees can archive long-term climate changes, but also short-term weather extremes by their growth responses and adjustment in wood anatomical structure. The variations in the width of tree rings and other wood parameters react differently to various environmental factors, depending on species and location. At cold-humid high-elevation sites, tree-ring width is often correlated with temperatures during the winter months before the growth phase, or with the mean temperature during the vegetation period. In contrast, tree growth in semi-arid mountainous environments is mainly limited by the available moisture conditions during the growing season. The maximum late wood density is a good indicator to reconstruct summer temperatures, while the isotopic variations of oxygen and carbon in tree-ring cellulose are sensitive to hydroclimatic climate parameters and evaporation. Quantitative analyses of the wood anatomical structure allow an extremely high temporal resolution of the stored climate information down to a few days. By combining several wood parameters with different seasonal sensitivities, a comprehensive reconstruction of the climate during the course of the year can be accomplished. Thus, tree-ring data can also be compared with other climate proxies, such as ice cores, lake sediments or runoff data, but additionally offer the advantage of an exact, year-accurate dating. In high mountain areas, this offers the opportunity to analyze landscape dynamic processes such as glacier fluctuations and geomorphological events using tree-ring data. With the help of long-living shrub species, tree-ring analyses can be extended into the alpine region above the tree-line

The Himalayan region has already witnessed profound climate changes detectable in the cryosphere and the hydrological cycle, already resulting in drastic socio-economic impacts. We developed a 619-yea-long tree-ring-width chronology from the central Nepal Himalaya, spanning the period 1399−2017 CE. However, due to low replication of the early part of the chronology, only the section after 1600 CE was used for climate reconstruction. Proxy climate relationships indicate that temperature conditions during spring (March−May) are the main forcing factor for tree growth of Tsuga dumosa at the study site. We developed a robust climate reconstruction model and reconstructed spring temperatures for the period 1600−2017 CE. Our reconstruction showed cooler conditions during 1658−1681 CE, 1705−1722 CE, 1753−1773 CE, 1796−1874 CE, 1900−1936 CE, and 1973 CE. Periods with comparably warmer conditions occurred in 1600−1625 CE, 1633−1657 CE, 1682−1704 CE, 1740−1752 CE, 1779−1795 CE, 1936−1945 CE, 1956−1972 CE, and at the beginning of the 21st century. Tropical volcanic eruptions showed only a sporadic impact on the reconstructed temperature. Also, no consistent temperature trend was evident since 1600 CE. Our temperature reconstruction showed positive teleconnections with March−May averaged gridded temperature data for far west Nepal and adjacent areas in Northwest India and on the Southwest Tibetan plateau. We found spectral periodicities of 2.75−4 and 40−65 years frequencies in our temperature reconstruction, indicating that past climate variability in central Nepal might have been influenced by large-scale climate modes, like the Atlantic Multi-decadal Oscillation, the North Atlantic Oscillation, and the El Niño-Southern Oscillation.

Stable isotopes of tree rings are frequently used as proxies in climate change studies. However, species-specific relationships between climate and tree-ring stable isotopes have not yet been studied in riparian forests in the savannas of West Africa. Four cross-dated discs, each of Afzelia africana Sm. (evergreen) and Anogeissus leiocarpus (DC.) Guill. &amp, Perr. (deciduous) in the humid (HSZ) and dry (DSZ) savanna zones of the Volta basin in Ghana were selected from a larger tree-ring dataset to assess the relationships between the tree-ring carbon isotope composition (&delta, 13C values) and climatic parameters. The atmospherically corrected &delta, 13C values of both studied species showed that A. africana was enriched in 13C compared to A. leiocarpus. Strong correlations were found between &delta, 13C values of A. africana and A. leiocarpus with temperature, but weak correlations with precipitation. Spatial correlation analysis revealed significant relationships between &delta, 13C values of both tree species and Sea Surface Temperatures in the Gulf of Guinea in the southern Atlantic Ocean. The results suggest that the carbon isotope composition of riparian trees in the Volta river basin has a potential to reconstruct climate variability and to assess tree ecological responses to climate change.

Xylem hydraulic adjustment to global climatic changes was reported from temperate, boreal, and Mediterranean tree species. Yet, the long-term hydraulic adjustment in tropical tree species has not been studied so far. Here we developed the first standard chronologies of three hydraulic trait variables for three South Asian moist forest tree species to analyze their long-term hydraulic responses to changing climate. Based on wood anatomical measurements, we calculated Hagen–Poiseuille hydraulically weighted vessel diameter (DH), potential specific hydraulic conductivity (KS), and vulnerability index (VX) and developed standard chronologies of these variables for Chukrasia tabularis, Toona ciliata, and Lagerstroemia speciosa which are different in their xylem structure, wood density, shade tolerance, growth rates, and habitat preferences. Bootstrap correlation analysis revealed that vapor pressure deficit (VPD) strongly positively influenced the xylem water transport capacity in C. tabularis, whereas T. ciliata was affected by both temperature and precipitation. The hydraulic conductivity of L. speciosa was mainly affected by temperature. Different adjustment strategies were observed among the species, probably due to the differences in life history strategies and xylem properties. No positive relationship of conductivity and radial growth was found, but a trade-off between hydraulic safety and efficiency was observed in all studied species.