Topic for Masters
This is a page for prospective master student interested in working in our lab. Here as follow a short list of little research projects is currently offered as possible topic for masters thesis. If you are interested in one of these projects or if you want to propose your own research topic please send your letter of interest, CV, and addresses of potential referees to patrick.fonti @ wsl.ch
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Reconstructing precipitation regimes over the last millennium from oak earlywood vessels
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
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Example of an automated earlywood vessel measurement
from a digital image.
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Linking wood cell anatomy to climate
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Tree rings have proved to be an invaluable source of environmental
information. Clear evidences of relationships between tree growth and the
environmental conditions have soon been identified and used by
dendrochronologists to look into the past. All these information are stored
into the characteristics of the rings, as the ring width, the density profile,
the chemical composition of the wooden matrix or the anatomical characteristics
of the cells.
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
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Three photomicrographs of
samples from a single larch tree growing in the Lötschental valley.
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Analysis
of the influence of May bug outbreaks
on oak wood anatomy
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Cockchafer (Melolontha melolontha L., colloquially
also called May bug) is an insect
beetle very abundant throughout Europe and which represented a major pest in the
periodical years of "mass flight" especially prior to the use of
pesticide introduced in the 1980s. Because of long development time as larvae,
cockchafers appear in a cycle of every three or four years, and in colder
climates even five years. These years vary from region to region. The imagos
(adults) have a voracious appetite and thus have been and sometimes continue to
be a major problem in agriculture and forestry where they feed by eating the
fresh developing leaves.
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
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Example of 3 year
cycles outbreak recognizable on a archeological wood piece
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