Dissertation: Dynamic variations in bark hydraulics

Tommy Chan presented his dissertation, Dynamic variations in bark hydraulics – understanding whole tree processes and its linkage to bark hydraulic function and structure, for public examination on 4 November 2016. Prof. Roderick Dewar from the Research School of Biology, The Australian National University, Canberra, Australia, acted as opponent. The dissertation will be published as part of the Dissertationes Forestales series.

A mature tree stem generally consists of a column of wood that is composed of a series of annual incremental layers and enclosed in a covering of bark. The dynamic variations of the bark are complex due to its structure and function: the thick outer-bark acts as a protective barrier against the abiotic and biotic environment; while the phloem is where sugar transport occurs. Much of the bark variation is due to the transport of sugars and its related processes. The xylem pathway, which transports water in the opposite direction, is connected to the phloem in parallel along the entire length of the stem. The immediate connection between these two transport pathways suggests a functional linkage

The purpose of this thesis is to study the dynamic processes that occur within the bark and its interaction with other internal tree processes and the external environment. These interactions have not been thoroughly quantified, especially on an intra-annual (e.g. daily) scale.

The thesis consists of four papers, of which one is a modelling paper and three are experimental studies. Growth is estimated with the model by separating the water-related influences from measured inner-bark, revealing a growth signal – proxy for cambial stem growth. Using this signal, a correlation study to microclimate variables is examined in one paper; and to assumed growth respiration in a second paper. The remaining two papers explore the seasonality of photosynthesis and respiration, and bark stem dynamics during the spring recovery period.

As a conclusion of this thesis, these papers show how inextricably linked individual tree processes and the environmental are to the changes within the bark. The culmination of this thesis opens new opportunities to further understand the dynamics of bark hydraulics and ecophysiological processes by implementing field measurements and state-of-the-art modelling.


Dissertation on Dissertations Forestales