The U.S. is struggling to replant forests destroyed by increasingly intense wildfires, with many areas unlikely to recover on their own.Researchers are studying which species are likely to survive — and where — as climate change makes it difficult or impossible for many forests to regrow. But they say the U.S. also lacks enough seed collection, seedling production and workers trained to replant trees on a scale needed to offset accelerating losses.The Forest Service says the biggest roadblock is the yearslong task of completing environmental and cultural assessments and preparing severely burned land for replanting.Here’s what to know:Climate impactLarger and more intense fires stoked by climate change destroy seed trees that normally allow regeneration or leave burn scars too large for trees to naturally bridge the gap.Climate has changed so markedly trees often can’t regrow. Even when seedlings take hold, drought and repeat fires often kill them.Especially hot fires also can harden the ground and leave barren slopes susceptible to washing away in rainstorms, polluting waterways. Researchers say some once-forested areas in the Southwest and West may never recover and instead will convert to grassland or shrubland.Reforestation gapNineteen of the 20 largest wildfires ever recorded in the contiguous U.S. have occurred in Western states since 2000, according to Sean Parks, a Forest Service research ecologist. That’s when the region slipped into an ongoing megadrought.The U.S. once was able to reliably replant burned forests. But now the gap between areas that need replanting and the ability to do so has grown to at least 3. …