Dieter Eckstein

Beitrag zur Rationalisierung eines dendrochronologischen Verfahrens und zur Analyse seiner Aussagesicherheit

Das in Mitteleuropa eingesetzte jahrringchronologische Datierungsverfahren wurde im Hinblick auf Rationalisierung und Aussagesicherheit geprüft. Als zeitliche Engpässe erwiesen sich die Probenentnahme, die Jahrringbreitenmessung, das Zeichnen der Zuwachskurven und vor allem der manuelle Kurvenvergleich. Durch Einsatz einer elektronischen Rechenanlage und anderer Hilfsmittel konnte der Ablauf beschleunigt werden. Für eine sichere Synchronisierung von Jahrringfolgen wurde der dafür gewählte Gleichläufigkeitswert, untersucht. Obwohl sich der Streubereich dieses Wertes bei synchroner und unsynchroner Deckungslage weitgehend überschneidet, gestattet der Gleichläufigkeitswert dennoch eine objektive Differenzierung, an Hand derer visuell eine sichere Altersbestimmung möglich ist. Ein Gleichläufigkeitswert resultiert aus den klimatisch geprägten, gleichsinnig verlaufenden Zuwachsschwankungen (Weiserjahre) und aus den zufällig sich deckenden Kurvenabschnitten. Die Werte beider Komponenten streuen. Erst wenn sich Werte au den beiden positiven Streufeldern summieren, liegt der daraus resultierende Gleichläufigkeitswert außerhalb der Zufallsstreuung. Zur Demonstration des modifizierten dendrochronologischen Verfahrens wurden einige Datierungsbeispiele angeführt. The dendrochronological dating method as used in Central-Europe has been analyzed with regards to accuracy and possibilities of rationalization. The drawing of samples, measurement of width of tree-rings, plotting of growth diagrams, and above all, the manual identification of tree-ring series has to be regarded as time-consuming. The use of a computer and other automated auxiliary apparatus enabled a speeding up of the dendrochronological process. The “Gleichläufigkeitswert” (coefficient of parallel variation),— as used for exact synchronization of tree-ring series— was investigated. Although the variation of this value overlaps to some extent in synchronous and in asynchronous position, it nevertheless permits an objective pre-classification by means of which an exact determination of age can be visually performed afterwards. The “Gleichläufigkeitswert” results from climatically determined, parallel-oriented increment fluctuations (Weiserjahre) and also from sections of growth diagrams which are congruent by chance. The values of both components vary. Only when the values of both positive variations are adding up the resulting “Gleichläufigkeitswert” will exceed the random variation. Examples of dating are given to demonstrate the modified dendrochronological method.

Studying global change through investigation of the plastic responses of xylem anatomy in tree rings

Variability in xylem anatomy is of interest to plant scientists because of the role water transport plays in plant performance and survival. Insights into plant adjustments to changing environmental conditions have mainly been obtained through structural and functional comparative studies between taxa or within taxa on contrasting sites or along environmental gradients. Yet, a gap exists regarding the study of hydraulic adjustments in response to environmental changes over the lifetimes of plants. In trees, dated tree-ring series are often exploited to reconstruct dynamics in ecological conditions, and recent work in which wood-anatomical variables have been used in dendrochronology has produced promising results. Environmental signals identified in water-conducting cells carry novel information reflecting changes in regional conditions and are mostly related to short, sub-annual intervals. Although the idea of investigating environmental signals through wood anatomical time series goes back to the 1960s, it is only recently that low-cost computerized image-analysis systems have enabled increased scientific output in this field. We believe that the study of tree-ring anatomy is emerging as a promising approach in tree biology and climate change research, particularly if complemented by physiological and ecological studies. This contribution presents the rationale, the potential, and the methodological challenges of this innovative approach.

The variability of vessel size in beech (Fagus sylvatica L.) and its ecophysiological interpretation

The vessel areas of ten beech trees growing on a dry site were measured separately for all tree rings using automatic image analysis. These data were correlated with the monthly amount of precipitation from the July prior to the growing season until the August of the current growing season. It is evident that vessel formation at the beginning of cambial activity is mainly controlled by internal factors. The rainfall in the previous summer and autumn and in the contemporary May had only a slight influence. Vessel formation towards the end of the cambial activity is strongly influenced by the July rainfall and is thus determined to a greater degree by external factors. These results are discussed on the basis of hypotheses of tree physiology.

Little change in the fir tree‐line position on the southeastern Tibetan Plateau after 200 years of warming

• As one of the worlds highest natural tree lines, the Smith fir (Abies georgei var. smithii) tree line on the southeastern Tibetan Plateau is expected to vary as a function of climate warming. However, the spatial patterns and dynamics of the Smith fir tree line are not yet well understood. • Three rectangular plots (30 m × 150 m) were established in the natural alpine tree-line ecotone on two north-facing (Plot N1, 4390 m asl; Plot N2, 4380 m asl) and one east-facing (Plot E1, 4360 m asl) slope. Dendroecological methods were used to monitor the tree-line patterns and dynamics over a 50-yr interval. • The three study plots showed a similar pattern of regeneration dynamics, characterized by increased recruitment after the 1950s and an abrupt increase in the 1970s. Smith fir recruitment was significantly positively correlated with both summer and winter temperatures. However, Smith fir tree lines do not show a significant upward movement, despite warming on the Tibetan Plateau. • The warming in the past 200 yr is already having a significant impact on the population density of the trees, but not on the position of the Smith fir tree line.

Is the growth of birch at the upper timberline in the Himalayas limited by moisture or by temperature

Birch (Betula) trees and forests are found across much of the temperate and boreal zones of the Northern Hemisphere. Yet, despite being an ecologically significant genus, it is not well studied compared to other genera like Pinus, Picea, Larix, Juniperus, Quercus, or Fagus. In the Himalayas, Himalayan birch (Betula utilis) is a widespread broadleaf timberline species that survives in mountain rain shadows via access to water from snowmelt. Because precipitation in the Nepalese Himalayas decreases with increasing elevation, we hypothesized that the growth of birch at the upper timberlines between 3900 and 4150 m above sea level is primarily limited by moisture availability rather than by low temperature. To examine this assumption, a total of 292 increment cores from 211 birch trees at nine timberline sites were taken for dendroecological analysis. The synchronous occurrence of narrow rings and the high interseries correlations within and among sites evidenced a reliable cross-dating and a common climatic ...

Tree-Ring Research on Tectona Grandis in Northern Thailand

From a network of teak chronologies in northern Thailand, 75 trees within one province were evaluated regarding their climatic signal. The raw tree-ring series revealed a high mean sensitivity of 0.50 and a moderate first-order autocorrelation of 0.48. The first principal component of the standardized data explained 44% of the total variation in the tree-ring data, indicating a considerable climatic influence on tree growth. The climate-growth relationship suggested that growth of teak in this study area is mainly controlled by rainfall from April to June. Thus, there is some promise that the whole network of teak chronologies in northern Thailand can contribute to reconstructing climate over at least the last three centuries.

Dendrochronological potential of the alpine shrub Rhododendron nivale on the south-eastern Tibetan Plateau

BACKGROUND AND AIMS Shrubs and dwarf shrubs are wider spread on the Tibetan Plateau than trees and hence offer a unique opportunity to expand the present dendrochronological network into extreme environments beyond the survival limit of trees. Alpine shrublands on the Tibetan Plateau are characterized by rhododendron species. The dendrochronological potential of one alpine rhododendron species and its growth response to the extreme environment on the south-east Tibetan Plateau were investigated. METHODS Twenty stem discs of the alpine snowy rhododendron (Rhododendron nivale) were collected close to the tongue of the Zuoqiupu Glacier in south-east Tibet, China. The skeleton plot technique was used for inter-comparison between samples to detect the growth pattern of each stem section. The ring-width chronology was developed by fitting a negative exponential function or a straight line of any slope. Bootstrapping correlations were calculated between the standard chronology and monthly climate data. KEY RESULTS The wood of snowy rhododendron is diffuse-porous with evenly distributed small-diameter vessels. It has well-defined growth rings. Most stem sections can be visually and statistically cross-dated. The resulting 75-year-long standard ring-width chronology is highly correlated with a timberline fir chronology about 200 km apart, providing a high degree of confidence in the cross-dating. The climate/growth association of alpine snowy rhododendron and of this timberline fir is similar, reflecting an impact of monthly mean minimum temperatures in November of the previous year and in July during the year of ring formation. CONCLUSIONS The alpine snowy rhododendron offers new research directions to investigate the environmental history of the Tibetan Plateau in those regions where up to now there was no chance of applying dendrochronology.

Annual increments of juniper dwarf shrubs above the tree line on the central Tibetan Plateau: a useful climatic proxy

BACKGROUND AND AIMS Dendroclimatology is playing an important role in understanding past climatic changes on the Tibetan Plateau. Forests, however, are mainly confined to the eastern Tibetan Plateau. On the central Tibetan Plateau, in contrast, shrubs and dwarf shrubs need to be studied instead of trees as a source of climate information. The objectives of this study were to check the dendrochronological potential of the dwarf shrub Wilson juniper (Juniperus pingii var. wilsonii) growing from 4740 to 4780 m a.s.l. and to identify the climatic factors controlling its radial growth. METHODS Forty-three discs from 33 stems of Wilson juniper were sampled near the north-eastern shore of the Nam Co (Heavenly Lake). Cross-dating was performed along two directions of each stem, avoiding the compression-wood side as far as possible. A ring-width chronology was developed after a negative exponential function or a straight line of any slope had been fit to the raw measurements. Then, correlations were calculated between the standard ring-width chronology and monthly climate data recorded by a weather station around 100 km away. KEY RESULTS Our study has shown high dendrochronological potential of Wilson juniper, based on its longevity (one individual was 324 years old), well-defined growth rings, reliable cross-dating between individuals and distinct climatic signals reflected by the ring-width variability. Unlike dwarf shrubs in the circum-arctic tundra ecosystem which positively responded to above-average temperature in the growing season, moisture turned out to be growth limiting for Wilson juniper, particularly the loss of moisture caused by high maximum temperatures in May-June. CONCLUSIONS Because of the wide distribution of shrub and dwarf shrub species on the central Tibetan Plateau, an exciting prospect was opened up to extend the presently existing tree-ring networks far up into one of the largest tundra regions of the world.

Wood formation in two species of Dipterocarpaceae in Peninsular Malaysia.

The wood formation of kapur (Dryobalanops sumatrensis) and tembaga (Shorea leprosula), growing under a weak seasonal climate in West Malaysia was studied over a four-year period using cambium marking. Technical problems arose from the heavy callus formation due to the wounding of the cambium, the small radial increment, and the high variability of the cambial activity around and along the stem. Wood formation in the two tree species appears to be a continuous process and not related to seasonality in rainfall and phenology.

The Influence of Rays on the Transverse Elastic Anisotropy in Green Wood of Deciduous Trees

Summary The green wood of twelve deciduous tree species was investigated regarding its radial and tangential moduli of elasticity measured in tension (ER and ET, respectively). In addition, the wood density and the volume fraction of rays were determined. A strong positive correlation was found between structural and stiffness properties. A simple two component model was derived for the relationship between the transverse elastic anisotropy factor (i.e., ER/ET) of the green wood and the relative volume fraction of the axial and ray tissues. In the radial direction of the wood, the modulus of elasticity is influenced by the wood density and the volume fraction of rays; in tangential direction only the density seems to be important. However, the comparison between the elastic anisotropy and the volume fraction of rays indicates that the rays may have an indirect influence due to their shape.