US forests are failing to keep up with climate change

However, at the current rate of warming, forests may not be able to adapt quickly enough to remain healthy, according to a study published Monday in the journal Proceedings of the National Academy of Sciences. This has negative implications for everything from carbon storage to biodiversity.

The study looked at forests in the western United States and found that they are evolving to cope with higher temperatures – what scientists call “thermo-drying” – becoming increasingly dominated by trees that are better able to tolerate heat stress. heat and drought.

Researchers from the University of California at Berkeley and the US Forest Service analyzed the composition of approximately 50,000 forest plots in western states over 10-year periods. The USFS undertook a decades-long effort to inventory the trees on these plots to monitor long-term changes, and researchers used that data and then mapped localized climate change data over it.

“Ideally, we should see a one-to-one relationship between tree heat tolerance and warming,” said Kyle Rosenblad, a doctoral student at the university and lead author.

While he and his team found that trees with a greater tolerance for higher temperatures and drier weather, such as the California juniper, are indeed gaining in dominance, climate change is outpacing these adaptations.

Equally concerning, Rosenblad said, is how the ratio of trees is changing. No new species appear in the forests. Instead, the change in composition occurs mostly because established species that prefer cooler, wetter conditions—the Douglas fir, for example—die or are weakened and attacked by insects.

This could lead to vast ecological changes over centuries or perhaps even decades. “Places that are forested today may only be able to support grasslands,” Rosenblad said. “No matter how hard we try, we may not be able to stop this.”

The United States has more than 32 million acres of old-growth forests on public lands, according to a study released earlier this month. These mature trees are particularly valuable because of their ability to store a large amount of carbon. The administration of US President Joe Biden is expected to use the information from this census as the basis for a new forest policy that would protect more old-growth timber.

However, as the study shows, stopping logging will not be enough. In recent years, rampant forest fires and beetle infestations have decimated millions of hectares of trees, being determined in part by rising temperatures.

“Even if there are forests left, the type of forest will be very different,” he added, “so for the people and animals that depend on these forests, this will be a drastic change and we have to start thinking about how we will adapt.”