The most widely used parameters in dendrochronology are tree-ring width and maximum latewood density, as these measures are directly affected by the prevailing climatic conditions during the growing season. Similarly, wood cell anatomical features such as cell size should also encode valuable climatic information. Time series of such cell anatomical characteristics might provide additional information about seasonal climatic variability.

Distinct spring precipitation signals have been obtained from annual changes in the size of earlywood vessels of living oak (Quercus sp.). Despite the potential to supply technique for obtaining information about seasonal precipitation signals for mesic sites in Europe, no long-term reconstructions from earlywood vessels currently exist.

In our Dendro Sciences Unit at the WSL, a method for rapid image analysis based on semi-automatic measurement of earlywood vessels has been developed. Archaeological oak samples spanning the last millennia are available from the Labor für Dendrochronologie for measurement. The successful applicant will collaborate with both labs in the development of a long-term reconstruction of precipitation for the Swiss plateau using oak earlywood vessels.

see Project description

Example of an automated earlywood vessel measurement from a digital image.

However, depending on species and environmental settings, this ecological information can appear strongly expressed or diffusely masked by other concurring information. More detailed mechanistic understanding of the process of environmental registration in tree rings is thus required to fully exploit this information. Thanks to continuously improving measuring techniques there is an improved capacity in looking with increased resolution into the tree-rings, which might opens new frontiers in environmental research towards the possibility to distinguish between different seasonal signals. An unavoidable and fundamental step towards a mechanistic understanding of the registration process is however the ability to provide a detailed description and timing of ring formation. When during the season, under which environmental condition is what structure produced, are fundamental questions in order to link cause and effect.

Since 2007, our Dendro Sciences Unit at the WSL is running a project in Lötschental where intra-annual wood formation is monitored along an altitudinal gradient. It is known which cell has been build at which time and climatic data during timing of formation have been collected.

see Project description

Three photomicrographs of samples from a single larch tree growing in the Lötschental valley.

During insect outbreaks trees can be completely defoliated which impacts tree growth and ring formation. These marks, which can be found in oak (Quercus robur and Quercus petraea) tree rings as well as in archaeological wood, can therefore be used to reconstruct past life cycles and to relate them to different climatic periods.

The goal of this master project is to identify wood anatomical structure in oak tree-rings that can be directly and uniquely related to May bug outbreaks.

- Is it possible to identify anatomical characteristics which are typical for outbreak years?

- Do outbreak years result in smaller annual rings with different anatomical structures?

- Is it possible to develop methods for the identification of outbreak years in order to build long term outbreaks chronologies?

- If possible, build a long outbreak chronology (several centuries).

see Project description

Example of 3 year cycles outbreak recognizable on a archeological wood piece