LÜNEBURG HEATH, Germany — At first Nancy Denecke couldn’t figure out why the sheep were panicking.

“It took me a moment to realize what was coming out of the forest,” said the 37-year shepherdess, recounting one eventful day last summer in northwest Germany.

She was grazing her herd in a treelined field when she saw the wolf pounce.

“Aiiieee,” she screamed, recording with her phone as she launched herself toward the shaggy, slinking figure that had locked on to one of her ewes.

“Get him!” she yelled to one of her dogs. The startled wolf disappeared back into the trees.

Virtually extinct in Germany for more than a century, wolves are flourishing here once again — a rare success story in a world of diminishing biodiversity. One factor: German reunification, which extended protections in the former West Germany to the former East. Their numbers have increased more than sixfold in the past decade, with Germany now home to as many as 161 packs, or about 1,300 wolves.

But accompanying their rebound are attacks on livestock — and an emotional debate.

The spread of wolves — through Germany and into Belgium, the Netherlands and beyond — has become an issue at the highest levels of the European Union. Last fall, it touched a personal nerve for European Commission President Ursula von der Leyen, when a wolf killed her pony outside her home in northwest Germany. She wrote later that the E.U.’s executive body recognizes “that the return of the wolf and its growing numbers lead to conflict.”