🔗 Share this article

Trees in Australia's tropical rainforests have achieved a global first by transitioning from serving as a CO2 absorber to becoming a source of emissions, driven by rising heat extremes and drier conditions.

Critical Change Discovered

This crucial shift, which impacts the stems and limbs of the trees but does not include the underground roots, started around 25 years ago, according to recent research.

Trees naturally store carbon as they develop and release it when they decompose. Generally, tropical forests are regarded as carbon sinks – absorbing more CO2 than they release – and this absorption is expected to increase with rising atmospheric concentrations.

However, nearly 50 years of data collected from tropical forests across Queensland has shown that this vital carbon sink could be under threat.

Research Findings

Roughly 25 years ago, tree stems and limbs in these forests became a net emitter, with more trees dying and insufficient new growth, as the study indicates.

“It’s the first tropical forest of its kind to show this symptom of change,” stated the principal researcher.

“We know that the moist tropics in Australia exist in a somewhat hotter, arid environment than tropical forests on different landmasses, and therefore it might serve as a future analog for what tropical forests will experience in other parts of the world.”

Global Implications

One co-author mentioned that it remains to be seen whether Australia’s tropical forests are a harbinger for other tropical forests worldwide, and further research are required.

But should that be the case, the findings could have significant implications for international climate projections, CO2 accounting, and climate policies.

“This paper is the first time that this critical threshold of a switch from a carbon sink to a carbon source in tropical rainforests has been identified clearly – not just for one year, but for two decades,” stated an authority on climate science.

Worldwide, the share of carbon dioxide taken in by forests, trees, and plants has been quite stable over the past few decades, which was expected to persist under many climate models and strategies.

But if similar shifts – from absorber to emitter – were detected in other rainforests, climate forecasts may understate heating trends in the future. “This is concerning,” it was noted.

Continued Function

Even though the balance between gains and losses had shifted, these forests were still playing an important role in soaking up CO2. But their reduced capacity to absorb extra carbon would make emissions cuts “a lot harder”, and necessitate an accelerated shift from carbon-based energy.

Research Approach

This study utilized a distinct collection of forest data starting from 1971, including records tracking approximately 11,000 trees across numerous woodland areas. It focused on the carbon stored above ground, but excluded the gains and losses below ground.

Another researcher emphasized the value of collecting and maintaining extended datasets.

“It was believed the forest would be able to absorb additional CO2 because [CO2] is increasing. But looking at these long term empirical datasets, we discover that is not the case – it allows us to compare models with actual data and better understand how these ecosystems work.”