By: Stephanie Pappas

Ancient trees, the venerable sentinels of forests, may preserve genetic diversity that helps woodlands thrive for thousands of years, a new study suggests. 

In a typical deciduous forest, the oldest of the old trees — many of which were standing during the First Crusade — can act almost like time-travelers, representing the forest as it stood centuries before most of the trees around it were saplings. These ancient trees may have taken root in very different environmental circumstances as most other trees in the forest, meaning their offspring may have advantages should the environment change again. 

Some species of trees are famous for living to mind-bogglingly ripe old ages: The White Mountains of California are home to unique populations of extremely long-lived bristlecone pines (Pinus longaeva), which can survive more than 5,000 years. California's Giant Sequoia (Sequoiadendron giganteum) has been recorded living longer than 3,000 years, as has the alerce (Fitzroya cupressoides) of Chile and Argentina. 

But even typical trees can have extraordinarily long lives, stretching for centuries. These ancients are now rare in North America thanks to logging and forest clearing, except  in a handful of places in the Pacific Northwest and in some parts of Appalachia, said Charles Cannon, the director of the Center for Tree Science at the Morton Arboretum in Lisle, Illinois. Surviving ancients are now mostly found in the tropics, in places like Borneo and the Amazon, Cannon told Live Science – and those forests are shrinking every day. 

"I am getting more and more convinced that they are quite important and do play a crucial role," Cannon said. "And once we lose them, they are gone. They are this property that emerges out of old-growth forests, out of centuries, and once we cut them down we're not getting them back."