On May 29, 1346, Philip VI of France was sitting in his castle at Brunoy, in the Forest of Sénart, trying to figure out how to make forests last forever. Not metaphorically forever. Actually forever—"perpétuellement," the ordinance said. The kingdom's forests must sustain themselves perpetually in good condition. His Masters of Waters and Forests would henceforth ensure that wood sales never exceeded what the forest could produce.

It was the first time a French king had officially admitted that forests could run out.

Three months later his army was butchered at Crécy and he spent the rest of his life begging for money and watching his kingdom fall apart.

Philip wasn't some enlightened conservationist. He was desperate. The Hundred Years' War had been grinding away for nine years. In April he'd called the arrière-ban—every able-bodied man in southern France had to show up for military service. His son was besieging Aiguillon with 20,000 men. The English were coming. He was hemorrhaging money.

And yet on that May morning, Philip took time to address a crisis that had been building for centuries. France had lost half its forests—from maybe 30 million hectares down to 13 million. Wood heated homes, built cathedrals, fired the furnaces that smelted iron. Paris was importing firewood from forests that kept getting farther away.

The kingdom was running out of trees. Philip knew it. Everybody knew it. What nobody had figured out was what to do about it when you also needed to raise armies and build ships and keep the forges running.

Philip's ordinance didn't just regulate cutting. It introduced an idea that wouldn't have proper language for 600 years: that a forest has a production capacity, that there's a line between use and destruction, that somebody needs to think about what's left for people not yet born. The word he used—soustenir, to sustain—would eventually become the root of the French translation of "sustainable development." He was groping toward something he couldn't quite articulate.

August 26, 1346. At Crécy, the French lost 1,542 noble men-at-arms in a single afternoon. Edward III captured Calais the following year. Philip spent his final years tormented by the length of the war, the defeats at Crécy and Calais, his subjects' refusal to finance the war adequately. He died in 1350, four years after issuing his forest decree, having watched nearly everything he cared about collapse.

His forest policy mostly failed—by 1820, France's forest cover had shrunk to just 12% of the territory.

But the idea didn't die. Three centuries later, Colbert's 1669 forest ordinance explicitly built on Philip's framework—and this one worked. Royal forest revenue quintupled in two decades. Nearly 50,000 hectares of woodland were recovered. The 1669 ordinance became the foundation for the 1827 Forest Code, which governed French forestry into the modern era.

Philip VI's attempt to think beyond immediate crisis had succeeded, just not in any way he could have witnessed. His dynasty ended. His war became a generational catastrophe. His kingdom fragmented. But the principle he articulated—that forests must be managed to sustain themselves—outlasted all of it.

Philip's ordinance had suppressed traditional usage rights in royal forests, transferring oversight from communities to royal officials. Colbert's version and the 1827 code reinforced these restrictions, depriving peasants of dead wood for heating, leaves for animal bedding, grazing rights. The resentment festered. In 1843—nearly 500 years after Brunoy—a state forest officer named Sergeant Ruty was murdered in the Forêt de Chaux. That year alone saw forest guards murdered across France—violence that continued almost through the end of the 19th century.

The forest policies that emerged from Philip's 1346 decree succeeded in preserving timber but excluded the people who'd depended on forests for survival. They reduced biodiversity through monocultural plantations. They worked in the narrow sense that France eventually stopped losing forests. They also created new injustices that lasted for generations.

Here's what happened: Philip VI issued his forest ordinance while preparing for a war that would devastate his kingdom. The ordinance mostly didn't work in his lifetime. The idea—that forests have limits, that someone needs to plan beyond the present crisis—proved more durable than armies or kingdoms or the men who commanded them.

The forests of France today cover about 31% of the territory, more than at any time since the Middle Ages. That recovery began with principles Philip VI articulated in 1346, was implemented by Colbert in 1669, and was codified in 1827. None of those men lived to see the forests recover. They just made choices about the distant future while their immediate worlds burned.

Philip VI sat in the Forest of Sénart on May 29, 1346, and tried to think about forever. Three months later he learned how little forever means when the present collapses. But the words he wrote that day—about forests sustaining themselves perpetually—outlasted his defeats, his dynasty, and his despair.