Wildfires Kill U.S. Forests, Climate Change Won't Let Them Regrow

Years after the 2000 Walker Ranch Fire, Tom Veblen, a forest ecologist at the nearby University of Colorado, Boulder, saw that grass and shrubs were regrowing in the charred foothills, but he had to search to find the rare baby version of the tall ponderosa pines that had dominated the area before the fire, Nathanael Johnson reported for the online environmental magazine Grist.

Photo Insert: New climatic conditions no longer support the growth of young pines.

One of his graduate students at the time, Monica Rother, who now leads her own lab at the University of North Carolina at Wilmington, took a closer look, formally sectioning off research plots and returning year after year to count little trees. More than a decade after the Walker Ranch Fire most of her plots had zero tree seedlings.

Kimberley Davis is a plant ecologist at the University of Montana and the lead author of an influential study on how climate change is altering forest regeneration after fire published in the Proceedings of the National Academy of Sciences (PNAS).

In her research, she found site after site where new climatic conditions no longer supported the growth of young pines. Adult trees can survive in conditions that kill their seedlings, but they have no future: Like the humans in the science-fiction movie “Children of Men” they’ve outlived their ability to reproduce.

With no seedlings, when a fire eventually passes through that is strong enough to wipe out mature trees, it means the woods are gone for good.

When trees fail to regenerate after a fire, new plants take their place. To generalize, in the northern Rocky Mountains, it’s a mix of grasses and shrubs of the genus ceanothus — like snowbrush. In the Southwest, juniper and oak savannas replace pine forests. In New Mexico, thorny locusts often dominate.

In northern California, it’s the dense hip to head-high thickets of manzanita and ceanothus. The general trend: Fewer forests, more shrublands.

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