Wood omens: What will the forests of the future look like?

In experiments that mimic conditions of the near future, some trees look set to thrive. With others, it's now a case of learning all we can before they’re gone.

It’s a bit like a dystopian forest fable.

Pipes pump carbon into the air above a contained canopy, in an experiment underway in the Amazon rainforest in Brazil. (Courtesy AmazonFACE)

Some trees are quietly preparing for the climate crisis, with a little human help.

They are doing this by leveraging networks with fungi and bacteria; they are entering into standoffs with certain kinds of microbes. Results are mixed but, in some cases, promising.

In experiments underway around the world, trees are essentially being introduced to atmospheric conditions that are expected to prevail by 2050.

After that point, researchers admit, the Amazon rainforest could be on its way to becoming a savannah or arid grassland. If that happens, it is hard to say what might become of the world’s trees (or humans and other life forms). Alternately, we may have mended our ways and be on our way to mending our world by then. So the current experiments are conducted in a spirit of scientific inquiry, readiness, and hope.

Here’s how they are going.

Old oak trees: The UK

One of the six experimental plots outside Birmingham . (Courtesy BIFoR FACE)

In a quiet forest on the outskirts of Birmingham is a patch of 180-year-old oak trees that have been transported to the future.

Across six experimental plots, eight-storey-high pipes supported by metal towers release air infused with carbon-dioxide above the canopy, elevating local concentrations of CO2 by 40%, to match the levels this region is expected to contain by 2050.

“Traditionally, it’s been thought that trees cannot adjust to changing atmospheric composition because they are ‘stuck in their ways’ and ‘locked into’ a closed cycling of nutrients with the soil,” says Robert MacKenzie, an atmospheric scientist and director of the Birmingham University Institute of Forest Research (BIFoR), which is conducting the experiment.

Over the course of seven years, the researchers have found that, in this instance, this simply isn’t true. The trees have responded to higher CO2 levels by raising their carbon-dioxide uptake by 20%, and logging a 10% increase in annual woody growth. This growth of trunk, root and branch helps them sequester more of the carbon in the air.

In a surprise discovery, BIFoR researchers also found that microbes in the bark could absorb significant quantities of methane, a climate benefit of trees not previously known (and a discovery that made global news last July).

The secret of the forest response appears to be a partnership with soil organisms such as fungi and bacteria, which absorb some of the pollutants and return nutrients to the trees, in exchange for the sugars and other food they cannot make themselves.

In an additional benefit, it turned out that the trees bounced back better after a heat wave. The high carbon levels and water-use efficiency helped them resume full-scale photosynthesis faster than a control group of untouched oaks nearby.

Results have been less than heartening, in the experiments conducted on eucalyptus trees in Australia. (Courtesy EucFACE)

In Australia, researchers at the University of Western Sydney have been conducting Eucalyptus Free Air Carbon-Dioxide Enrichment or EucFACE trials since 2012.

This “lab” consists of 160 million hectares of eucalyptus-dominated forest in the Cumberland Plain. The mission is to try to predict the effects of rising atmospheric CO2 levels on such an ecosystem.

The results have not been heartening, so far.

For one thing, elevated CO2 levels caused a significant decline in the populations of arthropods such as spiders and insects, which serve a crucial pest-control and nutrient-cycling function for these trees.

Adding to the crisis, in the nutrient-thin soil of this region, the eucalyptus trees’ symbiotic relationship with microbes appeared to collapse.

Despite the trees’ desperate pleas for phosphorus — in the form of more and more carbon released into the soil to feed the microbes — the microbes withheld the crucial nutrient for their own use, “leaving Eucalyptus trees with limited nutrition,” Kristine Crous, a senior lecturer at Western Sydney University, said in a statement.

This is important information because current climate models account for a boost in forest growth globally to help mitigate climate change. As MacKenzie of BIFoR puts it too, for any climate model to be even reasonably accurate, researchers will need a clearer idea of the role trees can be expected to play.

Lessons learnt in the Amazon: Brazil

The AmazonFACE project covers more than 400 tree species. (Courtesy AmazonFACE)

AmazonFACE in Brazil began in 2022.

This rainforest is nearing its tipping point, by some estimates (it has passed that point, by others). This means it either cannot, or soon won’t be able to, regenerate fast enough to retain its character as a rainforest.

The factors that have tipped it over include, of course, widespread deforestation, mining activity, the pollution of its land, air and rivers, and global warming.

It is estimated that, by 2050, this massive lung of the planet, spread across 6.7 million sq km (making it more than twice the size of India) will have begun its transition to the arid grasslands of a savannah.

The 10-year AmazonFACE project, funded by research agencies in Brazil and the UK and coordinated by the government of Brazil’s National Institute of Amazonian Research (INPA) and the University of Campinas, is the first such experiment in a tropical forest. It covers more than 400 tree species.

It is fundamentally an attempt to better understand this forest before it is lost.

Flourishing pines: USA

Some of the earliest pollution-adaptation studies in the world were conducted in the US.

In 1996, a Free Air Carbon-Dioxide Enrichment or FACE test was conducted on a set of 3,700 pine trees in the 7,000-acre Duke Forest, owned and managed by Duke University (whose main campus is spread across 9,000 acres). The young trees responded to increased atmospheric CO2 by absorbing more of it.

Only large-field manipulation experiments, however, can monitor the impact of increased carbon-dioxide on the ecosystem as a system, including soil composition and insect populations, says MacKenzie of BIFoR.

It takes many years to see the effect averaged over different growing seasons as it gets hotter, drier, cooler and wetter, at different times of year. “Ideally, this kind of study should have started, around the world, decades ago,” MacKenzie says.

By the time these projects began, the clock was already ticking. “AI and advanced statistics are now helping to draw out patterns as quickly as possible,” MacKenzie says.