As the gap between burned areas and replanting widens year after year, scientists see big challenges beyond where to put seedlings. The U.S. currently lacks the ability to collect enough seeds from living trees and the nursery capacity to grow seedlings for replanting on a scale anywhere close to stemming accelerating losses, researchers say. It also doesn’t have enough trained workers to plant and monitor trees. The Forest Service said the biggest roadblock to replanting on public land is completing environmental and cultural assessments and preparing severely burned areas so they’re safe to plant. That can take years — while more forests are lost to fire…