What if soil could tell us trees are stressed before the trees can?

On Dja Dja Wurrung country in North Central Victoria, technology developers Jacinta Plucinski and Akiba Wang load a collection of technology into their vehicle, parked in the generous shade of an ancient eucalypt at Nardoo Hills Reserve. The ute is full of sensors, antennas, solar panels, batteries, laptops and cables aplenty: it’s been a long day in the field.

The foliage of the Grey Box above them is a beautiful grey-green, but not far away, hundreds of eucalypts across 100 hectares of the reserve, look quite different. Branches on some trees are dead and bare, with buds sprouting from their trunks or bases (a response known as “epicormic growth”) while other trees are dead altogether.

Scientists from Bush Heritage Australia, who own and manage Nardoo Hills for conservation, first noticed with alarm this mass dieback event in 2014 after the region experienced 5 consecutive days above 40°C  ̶  twice in just over a month.

But rather than looking up at the eucalypt canopies, Plucinski and Wang – alongside Bush Heritage ecologist Dr Rowan Mott and others – spent their day focussed on the ground.

The team, which includes reserve managers, Monash University scientists and Dja Dja Wurrung traditional owners, is leading a groundbreaking project to collect data from below-ground ecosystems to identify indicators for above-ground ecosystem health.

In a landscape like Nardoo Hills, where future temperatures are predicted to be hotter and rainfall lower thanks to climate change, those indicators could make all the difference.

“So often we see evidence that our trees are not coping with the increasingly hot and dry conditions this landscape is experiencing,” says Mott. “The trees are our messengers. But what if there were messengers in the ecosystem that could signal stress before that point where the trees are dying? What if the soil could tell us?”

Traditionally, understanding soil health would have best been explored by taking soil samples, but these represent just a snapshot of soil quality at an isolated moment in time. Plus, says Justin McCann, who runs the Technology Advisory Group at Bush Heritage Australia, the process is laborious and time-consuming.

“You need to dig up soil samples and put them in bags, label and record their location, hike back to the vehicle, send them off to the laboratory for processing and wait for the results. So that’s a lot of work and delay before seeing the data.”

According to Dr Vanessa Wong, Associate Professor in soil science from Monash University, the soil can tell us, and now thanks to a new, low-cost monitoring system in place at Nardoo it is revealing changes in soil properties such as moisture, salinity, temperature, pH and carbon dioxide.

“Carbon dioxide levels, for example, can be a really good indicator of our below-ground ecosystem health,” says Wong. “If the microbes in our soil have a lot of food (or organic matter) they decompose that organic matter to release nutrients. And when they do that, they generate carbon dioxide – just like we do when we breathe. If that microbial respiration starts to drop off, then we get an indication that something is not quite right.”

“What we’re trying to do is get a gauge on how the microbes are functioning, and how they’re reacting to changes in the soil environment.”

These changes can be damaging (such as loss of moisture due to drought, or reduced CO₂ caused by compacted soils resulting from overgrazing) or beneficial (such as lower levels of salinity after revegetation of eroded areas).

Broadscale, long-term soil monitoring like this has never before been used in the Australian conservation industry. It is common in the profit-driven agricultural and mining industries, but has been inaccessible for the conservation industry due to the prohibitive cost of setting up, purchasing and maintaining the systems.

In 2020, Monash University soil science student Luke Richards approached Plucinski and Wang, (“the superstars of open-source environmental monitoring,” according to Richards) to help develop an offline soil-monitoring system for conservation.

Plucinski and Wang took Richards’ request one step further by making the system a real-time, wireless, in-situ system, to remove the barriers of cost and scalability for conservation organisations.

Plucinski says: “we started to ask ourselves, ‘how can we create a system that is much more scalable and affordable, to enable conservation ecologists to use similar sorts of basic infrastructure to start monitoring the below-ground impact of some of their conservation practices?’”

The pair had refocused their tech company, Freaklabs, in 2018 into the relatively new field of conservation technology, which has steadily grown momentum in the last five years.

And now, after four years in development they’ve finally installed the communications that allow data to be collected by sensors and transmitted to the computers of Bush Heritage’s land management team. For the conservation industry, this is entirely novel.

“Exploring the pricing and financial model is the next piece of the puzzle,” says Plucinski. “Our goal is to offer a system that’s tailored to conservation needs while remaining affordable.”

With a growing interest in adaptive management (which measures changes in key conservation targets as a response to management strategies) and funding bodies increasingly requiring impact reporting, data on soil conditions could offer powerful evidence to justify conservation expenditure and attract project funding.

One such restoration project is being implemented in the area of Nardoo Hills in which Wang and Plucinski spent the day installing the soil monitoring system, known as Spring Paddock, which has its own unique challenges. Spring Paddock is home to a natural spring all but hidden except for elusive seasons when it reveals its incredible hydrating ability.

“When functioning as it should, the spring seeps water slowly out of the hillsides after rain and from the groundwater table, filling in a mini-wetland which retains its water after months without rain,” says McCann. “But Nardoo has a grazing history and one of the impacts of that grazing is compacted soils.”

“Compacted soils make it harder to replenish the groundwater feeding the spring, and harder for seedlings to establish. And since we’re trying to restore this area of the property that was historically a woodland, that’s a problem.”

The strategies Bush Heritage has applied at Spring Paddock include applying netting into the ground to reintroduce ground cover, mulching, placing course woody debris and aerating heavily compacted soils. Real-time monitoring will allow the team to build a deep understanding of how these interventions impact soil health, which ultimately supports the above-ground ecosystems.

Now that the system is transmitting, long-term data collection and analysis can begin. The project aims to gather data for at least 12 months, but ideally years.

“From a scientific perspective, longer is better,” says Wong, referring to the ideal duration of monitoring. “When you’re linking weather and climate variables to what happens below-ground, there’s variability within days and between seasons, but then you also see departures from the long-term mean. We need to understand what’s natural variability and what’s a true step-change.”

Plucinski and Wang hope the application of this technology will stretch much further than just Nardoo Hills.

“I would hope that this technology is taken up by the conservation sector more broadly,” says Wong. “I hope that we consider soils in conservation much more than we have traditionally.”