Culturally significant trees: A brief TREENET case study

Greg M Moore
Burnley College, University of Melbourne
500 Yarra Boulevard, Richmond, Australia 3121

Introduction

The recognition of trees as important parts of our history and heritage is well documented. Ivens (1981) commented in relation to the historic trees of South Australia:

‘The tangible and visible history of our State, in the form of man-made monuments will take us back no more than 150 years, but trees are living monuments capable of transporting us 400 years into the past’.

The need for the recognition and protection of trees of heritage, landscape and biological significance in Australia has been an urgent matter in all Australian States for over 30 years (Moore 2001). It is both surprising and disappointing that over that time the long term preservation of such trees has not been guaranteed in any State despite the best efforts of organizations, such as the National Trust of Australia or the various attempts by State and Local governments to provide legislative protection.

The National Trust of Australia, Victoria has an active State register of significant trees, which utilises a set  of criteria (Table 1) for registering trees. None of the trees registered as heritage, notable or significant hase any legal standing that affords them legislative protection. Some can be linked to local government regulation or parliamentary statute, however, the real protection and value of such schemes is that they bring specimens to public attention and raise the public profile and interest in the future management of  the trees.

Table 1: Guidelines to the categories used for nomination of significant trees

Categories

1. Any tree which is of horticultural or genetic value and could be an important source of propagating stock, including specimens that are particularly resistant to disease or exposure.
2. Any tree which occurs in a unique location or context and so provides a contribution to the landscape, including remnant native vegetation, important landmarks, and trees which form part of an historic garden, park or tow
3. Any tree of a species or variety that is rare or of very localised distribution
4. Any tree that is particularly old or venerable.
5. Any tree outstanding for its large height, trunk circumference or canopy spread.
6. Any tree of outstanding aesthetic significance.
7. Any tree which exhibits a curious growth form or physical feature such as abnormal outgrowths, natural fusion of branches, severe lightning damage or unusually pruned forms.
8. Any tree commemorating a particular occasion (including plantings by Royalty) or having associated with an important historical eve
9. Any tree associated with Aboriginal activities.

The case study

The tree

The Separation Tree in the Royal Botanic Gardens in Melbourne is an old and significant river red gum, under which the separation of Victoria form New South Wales was celebrated in 1850. The tree was already mature at the time, and has long been registered by the National Trust of Australia as it meets many of the criteria listed in Table 1.

In August 2010 the tree was badly vandalised by someone who tried to kill it through ringbarking. Fortunately, the perpetrator(s) did not understand what they were doing:

• ring barking is a very slow killing process
• they probably meant to girdle but cutting the wood was too hard to do
• the tree did not wilt immediately as they had probably hoped
• there was the opportunity for remedial action

The tree was special in that it was or pre-European settlement age, historic, well-documented and growing in an ideal place for its future management. It was always going to get special treatment that would not be available, or even considered for other trees

Some tree anatomy and physiology

A proper understanding of the xylem and phloem transport systems is useful to a practicing arborist. Ringbarking is the removal of the bark to the cambium. It blocks phloem but not xylem transport. Water and nutrients get to the canopy from the roots, but if the break is wide enough for the tree not to grow over the wound then sugars and hormones do not get to the roots. The root system gradually starves and eventually the tree dies after 3-5 years.

Girdling is the removal of bark, cambium and xylem (usually the sap wood and some heart wood). Water transport is blocked and the canopy often wilts within 24-48 hours and the canopy above the cut dies

If bark is removed from a tree:

• to kill over the longer term a complete ring has to be removed so assess how much bark and cambium is intact (in this case about 20% was left)
• often as little as 10% of the circumference of bark is required for a tree to remain healthy
• replace any bark that you can immediately (in this case it took 3 days to replace the bark and some had dried)

Arboricultural management

A few days after the attack, all of the removed bark was put back in place and it was hoped that some of it might re-attach if the tree produced callus. The bark was held in place with nylon strapping. The damaged area was shaded, kept moist and protected. The tree was mulched and the soil moisture was monitored and maintained.

Unfortunately the tree did not produced callus that would have allowed the retention of the replaced bark and after about 6 months it fell off. However it was anticipated that much, if not all, of the bark that had been re-attached would be shed, and so this did not cause too much concern

The summer was mild and wet, and the tree remained healthy despite heavy insect grazing. It produced at least two flushes of new growth over the spring and summer after the damage. A thin band of callus has grown around the damaged surface, which gives some hope for the future. The spring of 2011 will be crucial in determining the future of the tree

So far things have gone as well as can be expected with the mild summer being a great benefit. It will be concerning if there is no evidence of greater callus production by the end of 2011, but old, large trees often take a few seasons to respond to damage. Humans want quick responses, but large, old trees move to their own rhythms of time and they are often much slower than ours.

The tree will be monitor regularly over the next few years. There is hope that there will be greater callus produced in the 2011 spring flush of growth. Once again care will be exercised with irrigation regimes and pest and disease protection, particularly over the coming summer.

Conclusion

The garden management, staff and contractors have been magnificent in their care and concern for the tree. While the long term prognosis is still uncertain, everything has gone as well as could be hoped. There is genuine reason to hope that the tree will still be making its historic contribution for many years to come.

References

• Ivens R (1981), Historic Trees of South Australia, Island Press, Kingscote, King Island
• Moore G M (2001) Ancient and Significant Trees: Protecting Community Assests and Heritage, in Management of Mature Trees, Proceedings of the 4th National Arborists Association of Australia, Sydney. Also available at www.nattrust.com.au