Trees can’t get up and walk away, but forests can
Trees can’t get up and walk away, but forests can
In fantasy worlds, trees like the Lord of the Rings’ Ents are agile and mobile. In the real world, they’re slow.

While individual trees can’t cross rivers and climb mountains, entire forests can. And climate change is making their journeys treacherous.
“Trees have been migrating forever,” says Leslie Brandt, an ecologist formerly with the U.S. Forest Service in St. Paul, Minn. During the last ice age, when an ice sheet covered most of Canada and the northern United States, many tree species took refuge in warmer, southern climates. As northern habitats got colder, seeds thrived in the warmer south. More new trees grew on the southern edges of forests, while older trees up north died out. Slowly, forests migrated, moving around 100 to 500 meters a year, Brandt says.
But now, human-caused climate change is altering habitats faster than forests can move. Rising oceans are threatening coastal mangrove forests worldwide. Higher temperatures in Canada are making it difficult for white spruce to grow. And drier conditions in the American Southwest are harming pinyon pines.