Dendrocronologia com base nos carvalhos europeus

K. Haneca, Tree-ring analyses of European oak: implementation and relevance in (pre-)historical research in Flanders, Tese de doutoramento, University Ghent, 2005.

A tese está livremente disponível aqui.

Resumo:

Throughout human history, forests and woodlands in Western Europe experienced a high anthropogenic influence. In densely populated areas forests were cleared and converted to arable land or were exploited for the supply of firewood and construction timber. In Flanders, it is estimated that the forest cover by the end of the 13th century was even lower than in the 19th century. To date, several assortments of timber, available on the local wood market during the Roman era and the Middle Ages, have become part of our cultural heritage. Archaeological remains, historical buildings, panel paintings and religious sculptures are only a few examples of constructions and objects that were created by processing wood. Especially European oak (Quercus robur L. and Q. petraea (Matt.) Liebl.) was highly esteemed by craftsmen. Tree-ring series of oak have the characteristic that they tend to crossdate. In other words, ring-width series display a certain element of synchronicity between remote sites. This feature allows to use dendrochronology, i.e. the scientific study of tree-ring patterns, as a dating tool. However, in Flanders tree-ring dating has seldom been applied and has often led to inconclusive results. Especially archaeological oak timbers or wood from historical buildings is often characterized by short (less than 50 years) and variable growth patterns. Therefore, it was assessed and demonstrated that such series have a potential for dating purposes and chronology building. It is believed that the high anthropogenic pressure on the original forest cover has stimulated the implementation of short rotation systems. Past forest management interventions and forest stand structure development are recorded in the growth patterns and the wood anatomical structure of archaeological and subfossil wood. By comparing them with growth patterns of contemporary trees from stands with well-known stand structure and management history it was noticed that the same patterns are encountered. Consequently, it is now possible to distinguish wood specimens that originate from, for instance, a coppice stand or a high forest by scrutinizing their growth patterns. Moreover, close observation of the wood anatomy, for instance, the size and distribution of earlywood vessels, provides an image of the variability in past hydrological conditions. Tree-ring series from wooden sculptures and panel paintings from 15th-16th century display a completely different nature. Since local timber sources mostly provided small sized and fast grown timber, craftsmen started to look for high-quality oak. Such assortments became available due to the establishment of an important timber trade. Especially oak timber from the Baltic region was imported. By studying the growth patterns on historical art objects it becomes clear that medieval woodworkers were well aware of the intrinsic variability and technological properties of the imported oak timber. Moreover, analysis of extensive datasets of tree-ring series from historical art objects provides more insights and information on the original timber source, wood processing activities and the creative process. It is obvious that dendrochronology has become more than a dating tool in (pre-) historical studies. This work demonstrates that it is highly valid to approach Flanders’ precious cultural heritage, created out of wood, from a multidisciplinary point-of-view, where archaeology, art-history, wood technology and biology should play an important and valuable role.