Unveiling the Hidden Crisis: How Climate Change is Transforming Australia’s Mountain Ash Forests

A troubling situation is unfolding in Australia’s mountain ash forests. These unique ecosystems, home to the tallest flowering plants on Earth, are losing trees due to rising temperatures. With each tree lost, their ability to store carbon diminishes.

Mountain ash forests, which can store between 415 and 819 tonnes of carbon per hectare, actually store more carbon than even the Amazon rainforest. This makes the decrease in these trees a significant environmental issue, both locally and globally.

Recent research highlights that these forests can’t sustain their current number of trees as temperatures increase. Data shows that for each degree of warming, the number of trees drops by about 9%. Projections indicate that by 2080, temperatures could rise by 3°C, resulting in a loss of up to 25% of trees.

Why does warming cause this tree loss? Trees in a forest compete for sunlight, water, and nutrients. If one tree gets more resources, others have less. This competition leads to a natural process known as “self-thinning,” where only the strongest trees survive as others weaken and die.

Warming exacerbates this process. Higher temperatures pull moisture from the soil and leaves, making it harder for trees to access the water they need. Trees that are already smaller and shaded by larger ones are particularly vulnerable. This can lead to increased death rates, especially during heatwaves or droughts.

Our study analyzed decades of data from forest management experiments between 1947 and 2000 in Victoria’s Central Highlands. We looked at how many trees the forest could support, known as “carrying capacity.” As forests become warmer and drier, their carrying capacity declines.

If tree loss continues, these forests could shift from being carbon sinks to sources, releasing stored carbon back into the atmosphere. Our findings indicate a loss of over 100 million tonnes of carbon by 2080, similar to emissions from a million cars driving for 10,000 kilometers each year for 75 years. This alarming trend is echoed by data from citizen science projects and other research across the country.

The implications of these findings extend globally. Tree-planting initiatives, like Trillion Trees, must consider the changing capacities of forests to support new trees. While forests in colder regions may benefit from longer growing seasons, areas like southeastern Australia face increased tree deaths and reduced carbon storage.

So, can we help these forests? Understanding how they adapt to warming is crucial. One potential solution is ecological thinning, which involves selectively removing some trees. This method can help remaining trees get the resources they need to thrive. Studies show that thinned forests are not only more resilient to drought but can also grow faster.

While we can’t halt climate change instantly, we can take steps to help forests adapt and remain healthy, ensuring they continue to play a role in our environment.

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