Prof. Susan Laurance from James Cook University has set up a rainfall exclusion experiment at the Daintree Rainforest Observatory – a location where Australia’s premium lowland tropical rainforest still predominate. Prof. Susan is studying the effect of drought on tropical rainforest trees, and in the past year I have been helping Prof. Sue’s PhD student Deborah Apgaua with one such axillary study on the trees earmarked for monitoring (Read more here and in the scientific article).
The study partly involved looking at the anatomical features of the wood of Prof. Susan’s study trees, which included a palm, two pioneer trees and five mature-phase rainforest trees. The wood was collected with a simple piece of forestry equipment, a increment borer, which was used to extract a small core of sapwood. Using fine grid sandpaper, we sanded the wood down until anatomical features was apparent and examined the samples under a microscope.
I was pretty amazed at the diversity of the anatomical features in the wood. What give wood it’s hardness and it beautiful brown colour are the fibres. And of course, wood contains vessels which enable trees to transport water to their canopies.
However, there are other structures such as parenchyma that help to give wood it’s distinctive appearance. These structures , and these structures have functional significance for a tree’s water storage or tensile strength.
For instance, Argyrodendron, Castanospermum and Syzygium has vessels distinctively associated with parenchyma. In the case of Castanospermum, the vessels are consistently encapsulated in patches of abundant parenchyma tissue which are sometimes form large confluent patches.
The vascular system of the single palm Normanbya (Black Palm) differs drastically from those of the other trees, consisting of dark scattered vascular bundles within a matrix of light-coloured ground tissue. Each vascular bundle is comprised largely of dense fibres with a single large vessel is situated at the distal end (into trunk). These fibres are also the reason why Black Palm wood is so hard and it is interesting to see how aboriginal clapsticks of the Kuku-Yalanji aboriginal people has such a fascinating anatomical basis.
My little foray into the inner workings of tropical trees has opened up yet another mysterious world for me to explore. And there will be more to say, as the study expands. Stay tuned.