Tree-ring analyses of European oak: implementation and relevance in (pre-)historical research in Flanders.

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

Growth trends reveal the forest structure during Roman and Medieval times in Western Europe: a comparison between archaeological and actual oak ring series (Quercus robur and Quercus petraea)

At some point in time, man has influenced nearly all forests in Western Europe. Most of the original forest cover has been converted to arable land and pastures, or has been cut for the supply of firewood and construction timber. In order to secure a sustainable source of firewood, the structure of the remaining forests was often altered. Especially coppice of European oak became increasingly popular during the Roman era and the Middle Ages. Ring-width series of oak trees from Roman times and Medieval settlements were recorded. In order to extract more detailed information regarding past forest structure and management, those series were compared to growth patterns of contemporary oak. The modern oaks were selected on forests sites in Flanders (northern Belgium) with well-known structure and management. Some remarkable similarities in growth patterns were observed. These findings yield tentative assumptions regarding past forest structure and management.Les tendances de croissance révèlent la structure des forêts en Europe Occidentale aux époques Romaines et Médiévales : comparaison entre séries d'accroissements annuels archéologiques et contemporains (Quercus robur et Q. petraea). Au cours de l’histoire, l’homme a influencé quasiment toutes les forêts en Europe. De grandes surfaces boisées ont été transformées en champs et pâtis ou ont été abattues pour récolter du bois de chauffage et de construction. Pour s’assurer d’une source durable de bois de chauffage, la structure des forêts restantes a souvent été adaptée. Surtout les bois de taillis de chêne sont devenus très populaires pendant la période romaine et au Moyen Âge. Des séries dendrochronologiques de chênes provenant d’établissements romains et médiévaux ont été analysées. Pour obtenir plus d’informations précises concernant la structure et la gestion des forêts antérieures, les séries ont été comparées avec celles de chênes contemporains. Ces chênes modernes ont été sélectionnés dans des forêts, avec des structures bien connues, situées en Flandres (Belgique). Quelques similarités remarquables observées dans les modèles de croissance ont permis de formuler des hypothèses concernant la structure et l’aménagement des forêts antérieures

A century of tree line changes in sub-Arctic Sweden shows local and regional variability and only a minor influence of 20th century climate warming

Aim Models project that climate warming will cause the tree line to move to higher elevations in alpine areas and more northerly latitudes in Arctic environments. We aimed to document changes or stability of the tree line in a sub-Arctic model area at different temporal and spatial scales, and particularly to clarify the ambiguity that currently exists about tree line dynamics and their causes. Location The study was conducted in the Tornetrask area in northern Sweden where climate warmed by 2.5 degrees C between 1913 and 2006. Mountain birch (Betula pubescens ssp. czerepanovii) sets the alpine tree line. Methods We used repeat photography, dendrochronological analysis, field observations along elevational transects and historical documents to study tree line dynamics. Results Since 1912, only four out of eight tree line sites had advanced: on average the tree line had shifted 24 m upslope (+0.2 m year-1 assuming linear shifts). Maximum tree line advance was +145 m (+1.5 m year-1 in elevation and +2.7 m year-1 in actual distance), whereas maximum retreat was 120 m downslope. Counter-intuitively, tree line advance was most pronounced during the cooler late 1960s and 1970s. Tree establishment and tree line advance were significantly correlated with periods of low reindeer (Rangifer tarandus) population numbers. A decreased anthropozoogenic impact since the early 20th century was found to be the main factor shaping the current tree line ecotone and its dynamics. In addition, episodic disturbances by moth outbreaks and geomorphological processes resulted in descent and long-term stability of the tree line position, respectively. Main conclusions In contrast to what is generally stated in the literature, this study shows that in a period of climate warming, disturbance may not only determine when tree line advance will occur but if tree line advance will occur at all. In the case of non-climatic climax tree lines, such as those in our study area, both climate-driven model projections of future tree line positions and the use of the tree line position for bioclimatic monitoring should be used with caution

Tree-ring analyses of European oak: implementation and relevance in (pre-)historical research in Flanders

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

Dendrochronologie en erfgoedonderzoek

Dendrochronologie is de meest precieze natuurwetenschappelijke dateringstechniek. Dat is meteen de hoofdreden waarom binnen de erfgoedwereld het archeologisch, het historisch en het bouwhistorisch onderzoek graag gebruik maken van de resultaten van een dendrochronologisch onderzoek. En toch is niet iedereen binnen deze vakgebieden reeds ten volle op de hoogte van de mogelijkheden van het dendrochronologisch onderzoek. Nog te vaak verdwijnt oud hout, zonder dat het onderzocht is, bij archeologische opgravingen, bij de restauratie van bouwkundig erfgoed of bij de omgang met levend houtig erfgoed in onze landschappen. Het onderwaarderen van oud hout als informatiebron in de context van erfgoedstudies heeft vooral te maken met een onderschatting van het potentieel aan informatie dat dendrochronologisch onderzoek kan bieden, niet enkel in een puur wetenschappelijke context maar ook in dossiers rond bescherming, behoud, beheer en studie van het boven- en ondergrondse erfgoed. Bovendien is er nog wat onzekerheid over wat de selectie van materiaal of staalname voor dendrochronologisch onderzoek precies inhoudt. Om de nodige kennis en ervaring te versterken, is wat toelichting op zijn plaats, en wil deze handleiding een houvast bieden

Historisch bouwhout uit Vlaanderen: import uit noodzaak? Dendrochronologisch onderzoek als bron voor houthandel en -gebruik

In Flanders, large-scale exploitation of the landscape was initiated in the tenth century by abbeys and by powerful landowners like the Count of Flanders. As a consequence, a lot of forested areas were converted into arable land and the remaining forest and woodlands became highly fragmented. It is estimated that in Flanders the lowest forest cover ever was reached by the end of the thirteenth century. It is known that from the thirteenth century onwards, Flemish towns imported massive amounts of construction timber. However, the wholesale depletion of local forests and the associated timber supply is contradicted by many archaeological discoveries of wooden structures built from local material. The provenance of such historical timbers can be determined by tree-ring analysis.Most probably, scarcity was not the sole factor behind the large-scale importation of construction timber. Quality, or rather the lack of high quality-timber on the local market, must also have played a role. During the Middle Ages the practices of coppicing and coppicing with standards were widely applied. These types ofwoodland management are highly productive and make it possible to harvest firewood and small-sized lumber in a relatively short time. However, these management practices are not best suited to the production of large quantities of straight-grained and high-quality construction timber.Due to the lack of large quantities of high-quality local timber, the importation of construction timber became increasingly important. An examination of the fourteenth and fifteenth century municipal accounts of several Flemish cities reveals that at least three major source regions can be identified for the timber imported into Flanders: the Baltic harbours and Scandinavia in the north, the forests along the Rhine, and the Ardennes and Meuse regions in what is now southern Belgium. Dendrochronological research into roof constructions in Bruges, Ghent and Oudenaarde demonstrates that the timbers were often imported from forested regions along the River Meuse. The trees were felled, tied together to form a raft and floated downriver to the coast. Eventually, most of these rafts arrived at the timber market in Dordrecht, from where they were shipped to Damme, the port for Bruges. In the Bruges municipal accounts, the town of Dordrecht is frequently cited as the place where timber was purchased for civil construction projects. This timber was also in demand further inland where it was used for large roof constructions. Although it is known that Baltic oak was imported, such timbers were never used for construction, but for more delicate applications such as panelling, staves or sculptures.A constant feature of medieval wood construction in Flanders is the use of oak, with only a few known examples of elm being used instead. Coniferous wood, although mentioned in the municipal accounts, was rarely used in historical wooden construction in Flanders.During the Middle Ages, widespread human intervention in local forests (timber harvesting, conversion to farmland), left them highly fragmented. While still able to produce everyday construction timber, local forests were no longer able to meet the ever-growing demand for high-quality construction timber