COLORADO—Six years ago, forest ecologist Marin Chambers looked toward the mountains with trepidation as a massive plume of smoke filled the sky above the largest wildfire in Colorado’s history. In June, she looked for clues to what the future forest might look like. …There is no guarantee that this high-elevation forest will come back as it was before. Many of the spruce trees were dead well before the fire hit, victims of an earlier beetle outbreak. The massive blaze killed much of what remained, burning so fiercely that vast swaths of land within the 845-square-kilometer burn scar were left with no living trees, limiting the cone crop needed to seed the next generation. A changing climate could pose a further obstacle to recovery. …Already there are signs that forest managers can’t count on natural recovery. …To prevent that transformation, some ecologists have proposed employing a forceful intervention called assisted migration.