Forests around the world face being permanently wiped out because climate change is making them unable to recover from devastating wildfires.

Solomon Dobrowski at the University of Montana and colleagues painstakingly dug up approximately 3,000 small trees from 90 burn sites across the western US to look at the ability of forests to regenerate after a wild fire.

They found that before the 1990s, low-lying forests could grow back after being burned, but between the early 1990s and 2015 there was a sharp drop in the ability of seeds to regenerate a forest at most sites.

The team used tree ring dating to see which year their trees had germinated since a fire, and used those samples to build a model of how forests would likely recover in different conditions.

Climate change appears to have changed soil moisture and surface temperatures so much that the forests have passed a threshold where conditions no longer favour new growth after a fire. Unlike mature trees, seedlings’ roots are too shallow to reach water deeper underground.

Higher temperatures

Climate scientists have warned for years of the possibility of such abrupt responses to higher temperatures, such as the rapidly-accelerating loss of ice sheets .

“These dramatic disturbance events, the changes we will see over the landscape won’t be gradual over decades, they will happen very quickly,” says Dobrowski.

The study looked at just two types of conifers, ponderosa pine and Douglas-fir. But Dobrowski said the findings were also relevant to similar semi-arid forests around the world, such as those of southern Europe.

That would be bad both in terms of the ecosystem services those forests provide, but also limiting future climate change.

Human interventions could help some of these burned forests grow back, for example by reintroducing seedlings when they are 2-3 years old and have roots long enough to reach water underground. But this costs money and time.

Meanwhile, more forests look set to burn – a study just last week found that in the future California faces wildfires potentially every year, regardless of rainfall levels.

Journal reference: Proceedings of the National Academy of Sciences , DOI: 10.1073/pnas.1815107116