🔗 Share this article

Australian tropical rainforest trees have achieved a global first by transitioning from acting as a carbon sink to becoming a source of emissions, driven by increasingly extreme temperatures and drier conditions.

Critical Change Discovered

This significant change, which impacts the trunks and branches of the trees but does not include the root systems, began approximately a quarter-century back, according to new studies.

Trees naturally store carbon as they develop and release it when they decompose. Overall, tropical forests are considered carbon sinks – taking in more carbon dioxide than they release – and this uptake is assumed to increase with rising atmospheric concentrations.

However, close to five decades of data gathered from tropical forests across Queensland has revealed that this essential carbon sink may be at risk.

Research Findings

Roughly 25 years ago, tree trunks and branches in these forests turned into a carbon source, with increased tree mortality and inadequate regeneration, according to the research.

“This marks the initial rainforest of its kind to show this symptom of transformation,” commented the lead author.

“It is understood 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 coming example for what tropical forests will encounter in global regions.”

Worldwide Consequences

A study contributor noted that it remains to be seen whether Australia’s tropical forests are a precursor for other tropical forests globally, and additional studies are needed.

But if so, the findings could have major consequences for global climate models, carbon budgets, and climate policies.

“This research 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 expert in climate change science.

Worldwide, the portion of carbon dioxide absorbed by forests, trees, and plants has been quite stable over the past few decades, which was assumed to continue under many climate models and strategies.

But if similar shifts – from sink to source – were observed in other rainforests, climate forecasts may underestimate global warming in the future. “This is concerning,” it was noted.

Continued Function

Although the balance between gains and losses had changed, these forests were still playing an important role in soaking up CO2. But their reduced capacity to take in additional CO2 would make emissions cuts “more challenging”, and necessitate an accelerated shift from carbon-based energy.

Research Approach

This study utilized a unique set of forest data dating back to 1971, including records tracking roughly 11,000 trees across 20 forest sites. It considered the carbon stored above ground, but excluded the gains and losses below ground.

Another researcher emphasized the importance of collecting and maintaining long term data.

“It was believed the forest would be able to store more carbon because [CO2] is increasing. But examining these long term empirical datasets, we find that is not the case – it allows us to compare models with actual data and improve comprehension of how these ecosystems work.”