Trial time

Eleanor Hetharia, Bush Heritage’s Head of Region South-East, will never forget what she saw at Nardoo Hills Reserve in early 2014.

“It was just a grey landscape. The green leaves had fallen.” It was on the back of the Millennium Drought, when rainfall in central Victoria was the lowest on record. The reserve, halfway between Melbourne and Mildura on Dja Dja Wurrung Country, had experienced two unexpected heatwaves in quick succession. Mature trees, already stressed, couldn’t take another hit.

While some trees managed to resprout, the mass mortality brought the future threat of climate change crashing into the present for staff and volunteers. With the CSIRO and the Bureau of Meteorology predicting hotter, drier weather for Nardoo Hills, our team analysed the odds of an event like this happening again and began questioning, “What could be done to improve the trees’ chance of survival?” This seeded the beginning of the Climate-Ready Revegetation Research Project.

The trees most affected by the 2014 dieback were Yellow Box (Eucalyptus melliodora) and Grey Box (E. microcarpa). One of our stalwart volunteers, Dr Garry McDonald started thinking about what could be done to prepare our reserves for future climate shocks. Garry was an entomologist at the University of Melbourne until his retirement in 2016, so he called upon his former science colleagues for suggestions.

Together, Garry, his colleagues and Bush Heritage ecologists hatched a plan to try ‘climate-adjusted provenancing’. This idea, first floated in 2015 by CSIRO scientists, is to source seeds from areas that are similar in climate now to the climate predictions for the parcel of land undergoing revegetation.

The idea is that Yellow Box and Grey Box growing in warmer and drier regions have already evolved to be more resilient to such conditions.

Collecting their seeds and planting the propagated tubestock at Nardoo means genes for hot and/or dry-weather resilience are introduced to the neighbourhood. When bees move pollen from flowers of the trial trees to flowers of trees already on the reserve, the expected result is seed with some genes that are advantageous under hotter, drier conditions. It is hoped that the trees that germinate from this seed fare better under future heatwaves.

Using a CSIRO tool that draws parallels between present climate in one location and future climate in another, the team identified four regions for seed gathering for each species, which corresponded to predictions ranging from severe climate change to more moderate climate change. Seed specialists from across New South Wales and South Australia volunteered to source the best seeds.

Then, through 2019 and 2020 with the support of Greenfleet and Arborline Nursery, the precious seeds were nurtured and planted on Nardoo. The team also cultivated local seed for comparison.

The science experiment took a hit in the first few months, with very dry weather and weeds taking their toll on the tiny trees.

But since April 2020 around 94% have survived, meaning 5,324 trees remain at the time of writing, some of them reaching six metres high. These trees are being monitored for height, girth, and other measures such as how much insect damage a tree might have. The monitoring is the combined effort of staff and dedicated volunteers.

Rowan Mott, ecologist for Bush Heritage’s South-East, says the project will determine whether bringing in seed from afar is a worthwhile strategy for future revegetation projects. Climate change related dieback is not only a problem for Nardoo, but around the country, and the world.

So far, the Yellow Box seeds sourced from Junee, New South Wales, seem to be surviving slightly better than the local saplings.

But Rowan cautions that it’s very early days. It’s possible that some of the young trees might have concentrated their efforts into putting down roots, rather than shoots, and that such trees might be more resilient if the present wetter weather dries up. “Trees that are coming in from drier locations might not have actually been challenged yet,” he says. While not wishing for drought conditions, Rowan says his scientific curiosity will fire up when Nardoo encounters a dry spell.

Supported by funding from Eucalypt Australia, ecologists are also working with academics from La Trobe University to undertake genomic analysis on the trees to provide tangible evidence that genetic differences exist among provenances within the research trial.

It will also allow us to track the relative genetic contribution of climate-adjusted or local provenances to new seedlings that germinate on the reserves. These efforts will provide valuable insights as the trees experience weather extremes and changes.

Preparing Nardoo for the reality of climate change is of vital importance. The reserve sits on the border of multiple different bioregions, making it a melting pot for species’ diversity.

Shy Heathwrens and Yellow-plumed Honeyeaters flutter about the mallee country to the north, while Diamond Firetails and Black-chinned Honeyeaters chirp among the Box-Ironbark woodlands to the south. Ecologists and reserve staff even discovered an orchid (Pterostylis valida) that was thought to be extinct for several decades.

The real results of the project won’t be known for a long time, as we wait to see how much the climate changes.

Meanwhile, the data are being shared with scientists at the universities of Melbourne, La Trobe and Macquarie. Already, two papers describing the trial have been accepted to scientific journals, and a PhD student, Rhys Browning, is writing his thesis on the experiment, with support from Bush Heritage donors.

Last autumn, some experimental trees showed they are already reaching reproductive age, with the first fuzzy blossoms beginning to unfurl.

As the trial continues, we can only ponder, with some excitement, how far their pollen might move and how long it takes for nature to select the next generation of resilient trees •

We gratefully acknowledge the many volunteers and partners involved in the project, and in particular, Eucalypt Australia’s funding towards genomic research.