Bräuning A (1999)
Publication Language: German
Publication Type: Authored book, Volume of book series
Publication year: 1999
Publisher: J. Cramer in der Gebr. Borntraeger Verlagsbuchhandlung
Series: Dissertationes Botanicae
City/Town: Berlin Stuttgart
Book Volume: 312
Pages Range: 164
Edition: 1
ISBN: 978-3-443-64224-2
URI: http://www.schweizerbart.de/publications/detail/isbn/9783443642242/%23
This study presents a the climatological results of a tree-ring study conducted in Eastern Tibet. The majority of the investigated sites are located at the timberline, so tree growth is primarily controlled by temperature. In total, 51 ring width chronologies from the trees of the genuses Picea, Abies, Larix, Pinus and Juniperus were compiled, the longest one from Juniper spanning 1546 years and dating back to 449 A. D. Furthermore, 20 chronologies of maximum latewood density were established, which were - like some ring width series, too - combined at some neighbouring sites with similar ecological conditions to regional chronologies with high sample depth.
The sites of this sample network, which covers a large area, were divided into five dendroecological regions or growth provinces according to statistical tests like the sign-test, t-value, cross-correlation, Kendall's Tau and cluster analyses. In four of these regions which cover the moist eastern and southern margins of the Tibetan plateau and the mountain areas in the upper course of the meridional gorges, tree growth is mainly controlled by temperature. In contrast to this, growth is limited by the available moisture in the upper course of the Yarlung Tsangpo and at the western limit of forest distribution in Tibet.
The statistical variance and sensitivity obtained from the tree-ring series of this dry forest-steppe-ecotone show high values in contrast to subalpine sites and point to a strong climatic signal in the chronologies of this region. The degree of similarity between the tree-ring lokations was not constant during the last 200 years, but variable in the course of smaller climatic fluctuations. Higher teleconnections, which point to a stronger common signal caused by more extreme climatic conditions, occured in the first half of the l9th and in the second half of the 20th century. Less similarity can be observed in the second half of the 1 9th and in the first half of the 20th century, indicating stronger influence of local stand characteristics and less extreme climatic conditions.
The short period for which meteorological data series are available and which rarely span more than 40 years, and not seem to represent the amount of precipitation at the tree-ring sites adequately, made the use of simple statistics in the analyses of the climate-growth relationships advisable. In most cases, significant and ecologically meaningful relations between tree growth and controlling climatic factors could be derived applying correlation analyses and sign tests. Maximum latewood density is highly correlated with late summer temperature, ring width is strongly influenced by temperature conditions during the early winter months November and December prior to the growth scason. Growth rates of Juniper forests on southern exposures are determined by various climatic factors, firstly by the amount of precipitation during the growth year and by temperature during the vegetation period in the year prior to growth. In the dry growth province of southern Tibet, moisture conditions in the late summer of the year prior to growth play a decisive role for tree-ring formation. The quality of the statistical correlations between tree growth and climatic variables could be strongly improved by calculating regional means of tree-ring and climatic data within the predefined dendroecological regions.
Smoothed chronologies of maximum latewood density show a strongly coherent low-frequency signal on a regional scale. Nevertheless, like in ring width series too, local disturbance signals like forest fires can be detected. Coherent growth patterns in ring width chronologies do occur in the dry growth province in southwestern Tibet and between subalpine sites in central eastern Tibet. Chronologies of Juniperus oflen show a stronger impact on growth of the local site conditions. The combination of consideration of ring width variation with the temporal variability of tree-ring parameters like variance, interval trend and percentage of pointer intervals clearly improves the scope of dendroclimatological interpretations of Juniper-chronologies.
The periods from 800-86O, 920-104O, 1080-115O, 1410-153O, 1590-1680 with minimum temperatures around 1620-166O, furthermore 1695-1705, 1810-182O, 1830-1840 and 1905-1925 can be characterized as cool periods. Warmer conditions provailed aronnd 860-91O, 1150-138O, 1550-159O, 1675-169O, 1795-1805 and 1930- 1950. Dry phases in southern Tibet occured from 1750-177O, 1800-1805, 1820-1840, 1850-1865, 1885-1905, 1915-1930 and 1940-1955. Climatic fluctuations, which can be documented for the last 1000 years in the Northern hemisphere, like the Medieval Climatic Optimum and the Little Ice Age, occured in eastern Tibet essentially like in Middle Europe, althongh regional particularities in various climatic provinces of eastern Tibet can be shown.
APA:
Bräuning, A. (1999). Zur Dendroklimatologie Hochtibets während des letzten Jahrtausends. Berlin Stuttgart: J. Cramer in der Gebr. Borntraeger Verlagsbuchhandlung.
MLA:
Bräuning, Achim. Zur Dendroklimatologie Hochtibets während des letzten Jahrtausends. Berlin Stuttgart: J. Cramer in der Gebr. Borntraeger Verlagsbuchhandlung, 1999.
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