Arctic shrubs have a strong potential for climate and environmental reconstructions in the chronically understudied regions of the high northern latitudes. The climate dynamics of these regions are ...important to understand because of large-scale feedbacks to the global climate system. However, little is known about other factors influencing shrub ring growth, possibly obscuring their climate signal. For example, as of yet we are not able to differentiate between herbivory or climatically induced growth depressions. Here, we use one of the most common Arctic shrubs, Alnus viridis as a test case to address this question. We sampled Alnus in Kobbefjord, Greenland, measured shrub-ring width and cell wall thickness and built site chronologies of each parameter. We analysed climate-growth relationships, tested their stability over time and employed a pointer-year analysis to detect growth depressions. We employed bootstrapped transfer function stability tests (BTFS) to assess the suitability of our shrub chronologies for climate reconstruction. Correlations with climate data showed strong significantly positive and stable correlations between summer temperature and ring-width with the exception of the recent decade. A climate reconstruction model failed stability tests, when the complete period of record was used for calibration and verification. Wood anatomy analysis uncovered the occurrence of unusual cell structure (very thin cell walls) in the exceptionally narrow ring of 2004, a recorded insect outbreak year in other parts of Greenland. When excluding the affected ring and a recovery period, the reconstruction model passed all tests, suggesting that the unusual 2004 ring was not climate driven, but rather the result of an insect attack. When combining anatomical analysis with traditional ring-width measurements, we move a step further in potentially distinguishing small rings caused by insect attacks from small rings formed in climatically challenging years. While this study does not provide unambiguous evidence, it does provide potential useful methodological combinations to enable more robust climate reconstructions in areas where climatic records are extremely sparse.
Climate change projections for Europe suggest increases in temperature, changes in precipitation regimes as well as more frequent and severe weather extremes like heat waves, droughts and storms. As ...these changes may have a large impact on forest ecosystems, forest management should adapt to maintain vital and productive forests in the future. This review assesses how close-to-nature silviculture (CNS), which is a widespread silvicultural approach in Central Europe, may cope with projected changes in climate. First, a conceptual model of forest vulnerability is outlined, and used to describe climate change exposure, sensitivity and adaptive capacity of forests. Strategies and options for adaptation, and their compliance with the principles of CNS are then discussed. Modifications in CNS, such as using exotic tree species and provenances or the assisted migration of well adapted tree species from other climates can enhance adaptive capacity of forests. Moreover, the regeneration of stress-tolerant pioneer species can be supported by applying the whole range of silvicultural systems. Keywords: climate change, adaptation, close-to-nature silviculture (CNS), tree species richness, genetic variation Projektionen zum Klimawandel in Europa deuten auf eine Erwarmung, Anderung der Niederschlagsverhaltnisse sowie haufigere und intensivere Witterungsextreme wie Hitzewellen, Trockenheit und Sturme hin. Diese Anderungen konnen einen starken Einfluss auf Waldokosysteme haben und die Waldwirtschaft sollte sich daran anpassen, um vitale und produktive Walder in der Zukunft zu erhalten. Dieser Ubersichtsartikel behandelt die Frage, wie der naturnahe Waldbau (close-to-nature silviculture--CNS) als weit verbreiteter waldbaulicher Ansatz in Mitteleuropa mit dem notwendigen Anpassungsbedarf der Walder im Einklang steht. Zunachst wird ein Konzept zur Abschatzung der Vulnerabilitat von Waldern unter Klimawandel vorgestellt. Danach werden die Vulnerabilitats-Komponenten 'Belastung', 'Empfindlichkeit' und 'Anpassungsvermogen' beschrieben und Strategien sowie Moglichkeiten fur die Waldanpassung und ihre Ubereinstimmung mit dem naturnahen Waldbau diskutiert. Modifikationen im naturnahen Waldbau, wie die Verwendung von eingefuhrten Baumarten und Baumartenherkunften sowie die unterstutzte Verbreitung (,assisted migration') von nachweislich gut angepassten Baumen aus anderen Klimaten konnen die Waldanpassung verbessern, ebenso die Erweiterung des Spektrums der Waldbausysteme zur Forderung von stresstoleranten Pionier-Baumarten. Schlusselworte: Klimawandel, Anpassung, Naturnaher Waldbau, Baumartenvielfalt, Genetische Variation
We investigated the temporal variability of intra-annual wood density variations in European beech (Fagus sylvatica L.) in a valley in southwestern Germany. Samples were collected from 11 beech trees ...growing at north-west (NW) and south-west (SW) exposed slopes. High-frequency densitometry was used to obtain wood density profiles. We converted radial positions within these profiles to a seasonal time scale over automatic point dendrometer data for the period 2001-2006. Temporally resolved wood density data was analyzed both visually and statistically, using correlation analysis and multiple linear regressions. Water availability was found to be of major importance for wood formation. Further, our results suggest that climatic forcing of wood density is not necessarily restricted to the late growing season only, but that strong associations may exist during a major part of the growing season. Combining wood property data with point dendrometer measurements was demonstrated to be valuable for increasing the understanding on the effects of changing environmental conditions on wood formation.
We analyzed inter-annual variations in ring width and maximum wood density of Norway spruce (Picea abies (L.) Karst.) at different altitudes in Baden-Württemberg, southwestern Germany, to determine ...the climate response of these parameters under contrasting climate conditions. In addition, we compared maximum, average and minimum wood density between sites. Bootstrapped correlation coefficients of ring width and maximum wood density with monthly temperature and precipitation, revealed a different climate sensitivity of both parameters. Ring width showed strong correlations with climate variables in the previous year and in the first half of the growing season. Further, a negative relationship with summer temperature was observed at the low-altitude sites. Maximum wood density correlated best with temperature during the growing season, whereby strongest correlations were found between September temperature and maximum wood density at the high-altitude sites. Observed differences in maximum, average and minimum wood density are suggested to relate to the local climate; with lower temperatures and higher water availability having a negative effect on wood density.
We investigated the temporal variability of intra-annual wood density variations in European beech (Fagus sylvatica L.) in a valley in southwestern Germany. Samples were collected from 11 beech trees ...growing at north-west (NW) and south-west (SW) exposed slopes. High-frequency densitometry was used to obtain wood density profiles. We converted radial positions within these profiles to a seasonal time scale over automatic point dendrometer data for the period 2001–2006. Temporally resolved wood density data was analyzed both visually and statistically, using correlation analysis and multiple linear regressions. Water availability was found to be of major importance for wood formation. Further, our results suggest that climatic forcing of wood density is not necessarily restricted to the late growing season only, but that strong associations may exist during a major part of the growing season. Combining wood property data with point dendrometer measurements was demonstrated to be valuable for increasing the understanding on the effects of changing environmental conditions on wood formation
