Queensland Rainforest Trees Shift from CO2 Absorber to Carbon Emitter in World First

Trees in Australia's tropical rainforests have become the first worldwide by transitioning from serving as a CO2 absorber to turning into a carbon emitter, due to increasingly extreme temperatures and drier conditions.

The Tipping Point Discovered

This significant change, which affects the stems and limbs of the trees but does not include the root systems, started around a quarter-century back, according to recent research.

Forests typically absorb carbon as they develop and release it when they decompose. Overall, tropical forests are considered carbon sinks – taking in more carbon dioxide than they emit – and this uptake is assumed to grow with rising atmospheric concentrations.

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

Study Insights

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.

“It’s the first tropical forest of its kind to display this sign of change,” commented the lead author.

“We know that the moist tropics in Australia exist in a slightly warmer, drier climate than tropical forests on other continents, and therefore it might serve as a coming example for what tropical forests will experience in other parts of the world.”

Global Implications

A study contributor mentioned that it remains to be seen whether Australia’s tropical forests are a harbinger for other tropical forests globally, and further research are needed.

But should that be the case, the results could have significant implications for global climate models, carbon budgets, and climate policies.

“This research is the initial instance that this critical threshold of a switch from a carbon sink to a carbon source in tropical rainforests has been definitively spotted – not merely temporarily, but for 20 years,” remarked an authority on climate science.

On a global scale, the portion of carbon dioxide absorbed by forests, trees, and plants has been quite stable over the last 20 to 30 years, which was assumed to continue under numerous projections and policies.

But should comparable changes – from sink to source – were observed in other rainforests, climate forecasts may understate heating trends in the future. “Which is bad news,” he added.

Continued Function

Even though the equilibrium between gains and losses had changed, these forests were still playing an important role in absorbing carbon dioxide. But their reduced capacity to absorb extra carbon would make emissions cuts “a lot harder”, and necessitate an accelerated transition away from fossil fuels.

Research Approach

The analysis utilized a distinct collection of forest data starting from 1971, including records tracking roughly 11,000 trees across numerous woodland areas. It considered the carbon stored in trunks and branches, but not the changes in soil and roots.

Another researcher emphasized the importance of gathering and preserving extended datasets.

“We thought the forest would be able to absorb additional CO2 because [CO2] is increasing. But looking at these decades of recorded information, we find that is not the case – it enables researchers to confront the theory with reality and improve comprehension of how these ecosystems work.”