Wildfires are permanently transforming conifer forests across the American West into shrubland, with scientists warning that up to 40 percent of Western conifer forests could shift by 2100. In the Sierra Nevada, the 2022 Oak Fire burned 1,700 acres of ponderosa pine, leaving no seedlings behind — only spiky shrubs and poison oak. Researchers say hotter, more intense fires combined with a warmer, drier climate have halted natural forest regeneration. "This is a permanent shift from one ecosystem type to a fundamentally different one," said Dr. Winslow Hansen, a forest ecologist at the Cary Institute of Ecosystem Studies in **Millbrook, N.

Y. The loss of forests accelerates snowmelt, threatening water supplies for communities that rely on snowpack for up to 75 percent of their water. It also reduces carbon storage, worsening climate change. Dr. Hansen, who grew up near Custer Gallatin National Forest in Bozeman, Montana, now leads the Western Fire and Forest Resilience Collaborative**, using satellites and climate models to track forest health. "The fires are just too hot for them," he said of ponderosa pines, which evolved with fire but not today's extremes.