Counting tree rings

Counting tree rings

Counting trees 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?). In Australia, Snow Gum (Eucalytpus pauciflora) from alpine areas, as well as native conifers such as King Billy Pine (Athrotaxis selaginoides), Huon Pine (Lagarostrobos franklinii) and Celery Top Pine (Phyllocladus aspleniifolius) from Tasmania, have distinct annual growth rings. Look at the moments in history when the King Billy Pine (below) was growing. Contrast this with the Australian Cypress Pine (Callitris spp.) where new wood rings would have been laid down in wet seasons but no new rings would have been left behind after drought years. Timber from the northern Hemisphere generally has very distinctive rings as seen in the huge Oregon pine. How old is this tree trunk?

Cross section of King Billy pine trunkCross section of Teatree trunk Cross section of Oregon Pine trunk 

Image: King Billy Pine; Teatree; Oregon Pine

How long can trees live? Until recently, a 4,850-year-old Bristle Cone Pine (Pinus longaeva) in the south-western arid zone of North America was thought to be the oldest tree alive. Very recently, a Norway Spruce (Picea abies) in Dalarna, Sweden, was found to be close to 10,000 years old!

While the oldest trees in the world are largely softwoods, there are some notable hardwood species that are very old. Olives (Olea europaea) has been dated to 3,000 years old in Sardinia, Italy. Biblical allusions to the Garden of Gethsemane refer to the olives trees that grow there to this day, many surviving for centuries in this harsh Mediterranean climate. The sacred Jaya Sri Maha Bodhi tree (Ficus religiosa) in Sri Lanka is said be 2,300 years old. Legend tells us that this tree was grown from a cutting of the original Bodhi tree under which Buddha received enlightenment.

The Australian mainland also has long-lived trees, although the tendency of fire to devastate eucalypt forests makes Australia’s hardwoods less ancient than those in other parts of the world. Eucalypts are likely to live for 100 to 400 years. In Tasmania, individuals of the softwood Huon Pine are at least 3,000 years old and some clones (small colonies of naturally occurring identical trees) might be 10,500 years old.

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