North America was once a loose, sprawling conversation between landscapes. Soft boundaries linked prairie, savanna, shrubland, forest and marsh. During a dry spell, lightning might spark a fire that burned for miles and days on end, relenting only when it hit a lake or river.

Remove fire, and this dialogue gets interrupted. Weedy scrub accumulates, stifling the earth.

“Ruderal junk — that’s what happens without fire,” said Bill Kleiman, project director at Nachusa Grasslands, a 3,600-acre preserve in Franklin Grove, Ill., operated by the Nature Conservancy.

Today, development and fragmentation have disrupted natural cycles of restoration in these landscapes. That’s why Mr. Kleiman’s team and many others across North America run controlled burns every spring and fall, helping sustain ecosystems that have been shaped by fire for millenniums. Here’s a glimpse into one such burn in April 2017 and the life that sprung up a few weeks later.