In Sequoia and Kings Canyon National Parks in California, trees that have persisted through rain and shine for thousands of years are now facing multiple threats triggered by a changing climate. Scientists and park managers once thought giant sequoia forests nearly impervious to stressors like wildfire, drought and pests. Yet, even very large trees are proving vulnerable, particularly when those stressors are amplified by rising temperatures and increasing weather extremes. The rapid pace of climate change – combined with threats like the spread of invasive species and diseases – can affect ecosystems in ways that defy expectations based on past experiences… To protect these places, which are valued for their natural beauty and the benefits they provide for recreation, clean water and wildlife, forest and land managers increasingly must anticipate risks they have never seen before. And they must prepare for what those risks will mean for stewardship as ecosystems rapidly transform.