Elizabeth Park has had the benefit of volunteers for over 14 years. Some of these have come from overseas. How appropriate one couple came from Sri Lanka. Both had degrees in Agricultural Science and were no strangers to hard yakka; pulling and chipping Bathurst burr from the Oasis Valley hills.
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You see, the connection is our silky oak trees planted on the same hills. Not only are silky oak (grevillea robusta) planted as street trees in Canberra, Cowra, Northern Territory, and North Dubbo, but they were grown in tropic countries like Sri Lanka as a shade tree for tea plantations.
The versatility of the tree is the key. Coming from north NSW around Coffs Harbour to Petrie in south Queensland, this tree will tolerate a lot more frost and dry than their natural habitat in rainforest would indicate.
Usually seen at 20 metres they can reach 30 metres and even occasionally a giant 37 metres. While some estimate the tree is short-lived around 50 years, others attest to twice that age.
A research project has been initiated in Oasis Valley by Dubbo Regional Council. We have a 10-year trial to test which recently used, street tree planting method is best for our Green Space Master Plan in planting trees in urban environments. This will affect all species, not just our test case ones. We are using 6 large metal skip bins, filled with a variety of soil mixes. The bins have been fitted with drainage pipes and the sides have been mounded up with on-site soil. Guess which trees we chose?
Quite right! The Silky Oak. We had some available from the Victoria Park re-plant. Two bins use the structural cell system; being Series 5 and 6 respectively recently used method in Brisbane Street. Another 2 bins use a modified version of the Stockholm System recently used in the Darling Street upgrade. Finally the last two bins use the Australian native landscape soil mix as a control in the experiment. That is, a mix of sand, crushed granite, mica and organics.
The Stockholm System uses biochar (form of charcoal produced by heating without oxygen). It increases soil fertility. European horticulturist Bjorn Embren successfully promoted it.
In 10 years we will open the bins and find out which system has the best root development.
This won’t stop tree planting now, but it will be beneficial for the future. In the meantime the graded slopes around the bins will be landscaped with groundcover planting. Which are best in Dubbo? Is it Creeping Myoporum? Maybe dwarf Saltbush, Eremophila or Strawberries?
I know which ones you want already. Let’s wait and see? Bring a pot of Ceylon tea and see it for yourself.
