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Gewählte Doctoral Thesis:

Sofia Pereira Leal (2008): Tree-ring growth trends in the Austrian Alps during the 20th century - Dendroclimatological approach to the study of the influence of recent climatic changes on tree growth.
Doctoral Thesis, BOKU-Universität für Bodenkultur, pp 92. UB BOKU obvsg

Data Source: ZID Abstracts
Abstract:
An extensive network of ring-width chronologies was established, comprising data from a total of 1206 trees sampled at 100 sites within the Austrian Eastern Alps, made up of five conifer species. At intermediate (no specific growth-climate signal) and high altitudes (tree growth is controlled mainly by summer temperature) three common periods of growth stand out: (1) a pronounced growth reduction during the mid-70s, already reported by several authors and associated with the unusual drought conditions felt during this decade in Central Europe; (2) a strong growth recovery during the 1980s, also pointed out in several other parts of the world, in response to a marked increase in temperature; (3) an apparent return to ‘normal’ growth rates at the end of the century despite the continued temperature rise. The reasons for this recent slowing down in growth are not clear but this feature raises the questions of whether the present forecasts are overestimating the amount of carbon that forests will be able to sequester in the future. At low altitudes (tree growth is determined mostly by spring-summer rainfall), analysis of the temporal stability of the relationship between tree growth show that, during the late 20th century, tree rings grew wider than expected. It is proposed that there was an improvement in water-use-efficiency arising from a stimulation of photosynthesis and declining stomatal conductance as a consequence of the increasing CO2 concentration in the atmosphere and that this effect was enhanced by a relatively high input of N due to the proximity of N emission sources. The divergence between the main growth-driving climatic factors and tree growth, found at the lowest and highest altitudes during the late 20th century, has important implications. Climate models based on tree growth might misinterpret climate trends over the past half of the 20th century. In addition, tree-ring based climate reconstructions might be impaired in their reliability.


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