Two metal blades are twisted deep into the trunk of one of the elderly elms lining St Kilda Road and slender, slightly damp cores of timber are removed. Just five millimetres thick, these fine snatches of wood are expected to be thick with information. The Ulmus procera is one of about 220 trees throughout the City of Melbourne being sampled to assess what species will grow best as our climate gets warmer, drier and prone to more extreme weather events.
Researchers have their eyes trained on the bands of colour along each sawn core of timber - the growth rings, the widths of which have long been known to vary from year to year according to environmental conditions.
Prompted by the release in 2012 of the city's first Urban Forest Strategy, the research ties in with the document's estimation that 39 per cent of the City of Melbourne's trees will be "at the end of their useful lives" within 20 years. With such a large proportion of specimens set to go, the big question is what to plant instead.
The City of Melbourne urban landscapes manager Ian Shears says dendrochronology - or the analysis of successive annual growth rings - is one of many ways in which the council is assessing which trees have performed best to date. But unlike visual assessments or the council's 16-year-old tree inventory and removal database, dendrochronology can reveal growth patterns dating to when the tree was planted.
Dr Craig Nitschke, a research fellow at the University of Melbourne's department of forest and ecosystem science, is conducting the tree-rings study. He expects some trees will reveal not just how they fared in Melbourne's most recent drought but also in the one more than a century ago.
Nitschke is from Canada, where he has regularly studied the annual rings of white spruces ("they have a beautiful ring, excellent for this methodology"). He says dendrochronology is used widely overseas, but it has limited application on trees that have a tendency to grow throughout the year - eucalypts, for example - because of the absence of a clear annual growth ring.
So while river red gums are one of the most commonly planted trees across the City of Melbourne, Nitschke has removed no cores from a Eucalyptus camaldulensis trunk as part of this study. Araucaria cunninghamii (hoop pine) and Agathis robusta (Queensland kauri) are, however, included, as well as oaks, poplars, planes, elms and conifers.
Two cores have been removed from each specimen's trunk, and these will be dried and then sanded until the light and dark bands of colour (stemming from the different density of wood produced early in the growing season compared with that produced later) stand out enough to be measured accurately.
The data will then be compared with climate records over the same period to assess how different species have responded to hot, dry times and, to a lesser extent, more mild, exceptionally wet ones.
While Nitschke expects to find narrow rings in times of drought, he says the question is whether those trees with particularly prolonged and marked narrowing experience long-term ill health. This would erode those specimens' environmental and community benefits, including their ability to provide shade and ameliorate air pollution.
The effects of air pollution will also be examined - funding permitting - by testing the cores for heavy-metal content. By quantifying the lead and other pollutants in the trunk samples, it will be possible to assess how pollution affects tree growth and health, Nitschke says.
The aim of this sampling and testing is an attempt to ensure the almost doubling of public-realm canopy cover across the City of Melbourne by 2040 - one of the targets of the Urban Forest Strategy - is done with ''smart species selection''.
Shears says now is the time to figure out what plants will grow best as the climate changes.
''We need to retain Melbourne's character and cultural heritage but blend it with the science and that's where words like robustness and resilience come up,'' he says.
Finding a balance between planting for both heritage character and future climate can be a juggle.
Public input will be sought at a series of ''community conversations'' run by the council, one of which has been scheduled for the city today.
When it comes to public trees, feelings run high. While drilling into the 220 trees for the dendrochronology study, Nitschke estimates about 200 passersby, police included, asked the researchers why they were piercing a tree trunk. ''It doesn't damage it,'' he says. ''The cells of the tree naturally swell around the wound and fill it with sap and resin. The worst thing you could do is to put something foreign in there to seal it up - that increases the chance of infection.''
■ A workshop for community discussion on designs of an Urban Forest Precinct Plan will be held on Saturday May 4, from 10am to 1pm, at the Multicultural Hub, 506 Elizabeth Street, city. To take part in an online forum, go tomelbourne.vic.gov.au/sustainability.