Tuesday, 1 March 2011

Elderly and persistent trees


As I draw to the end of my time as Executive Director of Sydney's Royal Botanic Gardens and Domain Trust, I've finally been through the back log of unblogged radio notes and this is my final blog 'from the archives'.

There are still a couple of current postings to come from my chats with Simon Marnie on his Weekend Show, on ABC Sydney Radio, and then it's over to Kew...

Fittingly, this one is all about things that persist, not things that leave after 12 or so years (or 7 or so years as Executive Director)... We often get asked what is the oldest tree in the Royal Botanic Gardens. The oldest planted trees are the Swamp Mahoganies (Eucalyptus robusta), planted in 1816 to the north of the Macquarie Wall.

These deteriorating trees are what are left of the oldest row of street trees planted in Australia, flanking the original alignment of Mrs Macquaries Road. A replacement row was planted in 2002, from seed sourced from La Perouse (seed collected from the trees themselves was not viable). It is struggling along.

The next oldest planted tree in the Royal Botanic Gardens is the Red Cedar (Toona ciliata) near the Palm House, collected from near Parramatta in 1822. The closest stands of Red Cedar are now probably in Royal National Park and Kurrajong.

The adjacent Broad-leaved Paperbark (Melaleuca quinquenerviai) was probably collected locally and planted sometime before 1828.

Then we have a few rainforest trees in the Palm Grove collected from the banks of the Brisbane River, on the John Oxley expedition to Queensland in 1828. Two early Directors, Charles Fraser and Alan Cunningham, travelled north with Oxley.

There are only a couple of apparently indigenous trees – Forest Red Gums – still surviving in the Gardens and Domain. These may be more than 192 years old, but it’s hard to confirm.

A few descendents of original bushland species are also dotted across the site: Swamp Oaks (Casuarina glauca) near the Maiden Pavilion, two Forest Red Gums (Eucalptus tereticornis) overlooking the Opera House, and maybe a Port Jackson Fig (Ficus rubiginosa) or two.

Assuming all these trees make it to our bicentenary in 2016, that’s quite an achievement. Lasting 180 to 200 years is pretty good for a city tree having to tolerate air pollution, disruption to its roots as paths and roads are constructed, and growing outside their natural climatic range or their protective forest habitat.

In the wild, trees can live for hundreds of years. River Red Gums in the Barmah Forest near Echuca are thought to be 400-500 years old. Bristlecone pines in California have been dated at 5,000 years, and just last year a spruce in Norway was found to be 8,000 years old.

Although we have Huon Pines in Tasmania dated at 10,000 years, these are probably ‘suckers’ from the original trees. If we allow suckering in our definition, there are various examples around the world of ‘trees’ that are more than 10,000 years old, including a Lomatia in Tasmania that is estimated to have begun life as a seedling 43,000 years ago.

Our Swamp Oaks will probably continue to sucker for many centuries, but the best we can do for our other trees is to care for them as long as we can and sometimes collect seed to keep alive the genetic lineage.

Image: Swamp Mahoganies old and new, some remaining from the oldest row of street trees planted in Australia. *This posting is the last from the Radio Archives (May 2009) - my blog started in November 2008 but I didn't start including my Passion for Plants (P4P) stories until May 2009, with 'Fruits of the Sky'.

No comments: