The long road to forest recovery after earthquakes

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When we think of earthquakes, our minds often go to the immediate human toll: lives lost, homes destroyed, and cities needing to be rebuilt.

But the impact on nature, particularly forests, is profound and lasts much longer than we might expect.

New research has shown that forests can take decades to recover from the damage caused by earthquakes, even longer than it takes to repair human infrastructure.

A striking example is the aftermath of the 1950 earthquake in Zayu-Medog, Tibet, where it took 45 years for the forests to fully bounce back.

Earthquakes can wreak havoc on forests by tearing trees apart and uprooting them. They also mess with the water and nutrients the trees need to survive.

Dr. Shan Gao and his team from the Chinese Academy of Sciences have looked into this issue by studying tree rings, which are the annual growth layers found in trees. This method, known as dendroclimatology, helps scientists understand past environmental conditions.

The team put together information on forests from the 1900s to today, covering seven mountain regions worldwide. This data represents 23% of the world’s forest cover.

By examining the tree rings closely, they could tell which changes were due to earthquakes and which were because of the climate.

They matched the tree ring data with known earthquakes over the last 120 years, using a special scale to measure the earthquakes’ strength.

Their research found that a significant portion of the tree sites they studied had been affected by earthquakes.

They then looked at how tree growth rates changed in the 20 years after these earthquakes, trying to figure out what conditions help or hinder forests’ ability to bounce back.

Dr. Gao’s team discovered that forests in dry temperate zones, like certain parts of North America, the Tibetan Plateau, and New Zealand, were pretty good at recovering. They found that after an earthquake, if there was more rain, these forests tended to grow back faster.

This was especially true for western North America, where recovery was quick and lasted for more than 20 years in some cases.

However, not all areas were as resilient. In places like the Tibetan Plateau and New Zealand, the forests struggled more with recovery, especially when there was less rain after an earthquake. This recovery process was slower, taking about 10 to 15 years.

One reason for the differences in recovery rates is how earthquakes change the soil. Strong shaking can create cracks and fractures, allowing rainwater to seep deeper into the ground.

This can help trees by giving them more water and nutrients, especially in areas like the Mongolian Plateau and the Mediterranean.

But in places with a lot of rain, like New Zealand, the shaking can lead to soil erosion and wash away important nutrients, which makes it harder for forests to recover.

Dr. Gao believes that while climate changes can affect forests for up to five years, the impact of earthquakes can last for 20 years or more.

This research is crucial for understanding how to protect forests, which are not only homes to diverse wildlife but also important in storing carbon, especially as the world faces the climate crisis.

It highlights the need for careful management of these natural areas to safeguard their recovery and preserve their role in the global ecosystem.

The research findings can be found in Nature Geoscience.

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