Dendrochronology is the art of interpreting tree rings to date wood tissues and document past events.
Trees - a window to the past
The secondary stems and roots of land plants lay down wood continuously, producing reinforced roots, powerful trunks and resilient limbs that can survive for millennia. A strong central cylinder of wood is characterised by growth rings. Genetics and environment control wood growth and thereby confer the physical and aesthetic qualities of each individual timber. But wood is slow to degrade so growth rings also tell us much about the past.
The display in the E8C ground floor foyer features cross sections of different trees from around the world, highlighting the beauty and the variation between different tree woods.
Counting Tree Rings
In cool temperate climates, wood rings are distinctive and one is laid down each year whereas in the hot savanna and arid zones, rainfall can be erratic, leading to new rings mainly in the wet years. Because seasonal conditions influence tree growth rates, a permanent record is captured in the appearance and chemical composition of growth rings.
Transects of many individual trees from one location must be analysed to match their rings if we are to have confidence in our interpretation (see What do tree rings tell us?).
What do Tree Rings Tell Us?
Tree rings are full of valuable information. They are especially informative about past climatic events and have great value when combined with other techniques in understanding climate change. Several climatic factors influence wood ring width and composition, particularly rainfall, temperature and carbon dioxide concentration.
Trees in Modern Australia
Woody plants, like all organisms, evolve continuously under selective pressure imposed by their environment. The superficial bark layers are very diverse, as you can see from the living trees of the Arboretum. Australian trees are particularly divergent.
Tree rings of a very old King Billy Pine
Look at the image of the King Billy Pine. [Or better yet, visit the display in the E8C ground floor foyer.] You can see wood rings extending just under 1,000 years! Each one tells us about past climate in Tasmania and helps piece together whether climate fluctuations are local or global phenomena.