Right now chestnut enthusiasts are cozying up next to their open fires (or toaster ovens) to roast a holiday snack that has long roots in North America. But the chestnuts they’re roasting aren’t native, because the American variety has been mostly wiped out by an invasive fungal blight since the 1930s. Researchers are laboring to bring them back, even as they have hit roadblocks and setbacks in attempts to breed or genetically modify a version that can withstand the blight. If and when they succeed, they’ll still need to figure out how to plant it and help it thrive in forests that are already under pressure from climate change, globalization and development.