TIVISSA, Spain — Forests are getting some high-profile attention lately.
President Trump expressed his support on Tuesday night for a global effort to plant one trillion trees, which itself was announced at a gathering of business and political leaders in Davos, Switzerland, in January. A trillion trees, it was said at that meeting of the World Economic Forum, would go a long way in addressing climate change.
But while trees — and particularly forests full of trees — are vital for swallowing up and storing carbon, currently absorbing 30 percent of planet-warming carbon dioxide, they are also extremely vulnerable in the age of climate disruptions.
In a hotter, drier, more flammable climate, like here in the Mediterranean region, forests can die slowly from drought or they can go up in flames almost instantly, releasing all the planet-warming carbon stored in their trunks and branches into the atmosphere.
That raises an increasingly urgent question: How best to manage woodlands in a world that humans have so profoundly altered? “We need to decide what will be the climate-change forest for the future,” is how Kirsten Thonicke, a fire ecologist at the Potsdam Institute for Climate Impact Research, framed the challenge.
Marc Castellnou, a 47-year-old fire analyst with the Catalonian fire services, has seen that shift firsthand here in the hot, dry hills of Catalonia, in northeastern Spain, where his family has lived for generations in a medieval village overlooking the Ebro River.
His mother’s family grew almonds up here. The terraces they once hacked into these hard rocks still remain, along with the brick oven of the old farmhouse and a row of juniper trees, which, by local custom, signaled to anyone walking up from the coast that they could barter their fish for bread there.
The almond orchard has long been abandoned. In its place, a scrubby forest of short oaks and white pines has come up. Where goats once grazed, there is now a carpet of dry grass. A perfect landscape for fire.
What happened with his ancestors’ farm has played out across Europe, profoundly altering the countryside over the past half century. As farmers walked away from the land in favor of less backbreaking, more profitable ventures, forests came back.
Now Mr. Castellnou has been setting some of those forests ablaze, getting rid of the grasses and low-lying shrub so the flames can’t as easily race up to the crowns of the young, frail pines. The last thing he wants his two young children to inherit is a hillside strewn with dry, flammable brush.
“Climate change is changing everything,” Mr. Castellnou said. “We’re trying to build some vaccination into the landscape.”
In Europe last year, wildfires raged as far north as Sweden. Drought and beetle infestations killed swaths of forests in Germany, prompting a debate over what trees to plant in their place. Britain had more wildfires last year than ever before on record. Spain saw one of the sharpest increases in the number of individual fires. The European Union described forest fires as “a serious and increasing threat.”
The forests of Europe have been shaped and reshaped by human hands over centuries. Trees were cut for fuel and timber, then terraced so farmers like Mr. Castellnou’s forebears could plant whatever would fetch the most money.
His ancestors chose a steep hillside and planted almonds. The grandparents of his wife, Rut Domènech, 39, cultivated hazelnuts. Nearly everyone had olives to supply oil for the year. Some grew grapes to make wine. Every bit of hill was under cultivation.
By the second half of the 20th century, Catalonians began abandoning the steepest, hardest-to-farm hillsides in favor of the valleys, where machines and fertilizers made farming easier and more productive.
Mr. Castellnou’s father gave up working on other people’s almond orchards altogether. He helped construct a new highway, then a new nuclear power plant in the next town, then went to work in a factory making wooden picture frames.
With the nuclear plant nearby, locals prospered. Ms. Domènech’s father found construction work. Her mother opened a boutique in the next town.
Farming fell out of favor. The shepherds sold their animals.
Across Europe, between 1950 and 2010, amid rapid postwar reconstruction, woods and grasslands grew by roughly 150,000 square miles.
“I’m really sad my grandmother didn’t want to show me the value of the land,” Ms. Domènech, a researcher at the Forest Sciences Centre of Catalonia, a government backed institution, said as she walked past one of the many abandoned stone farmhouses.
It’s as though, she added, they weren’t proud of who they were.
Wispy white pines took over the hillsides, crammed tightly next to each other. Grasses grew tall.
As Catalonians migrated to cities, the fingerprints of climate change also emerged. Heat records were broken, one after another. The grass turned dry. The white pines began to drop their needles.
Farmers in the Montsant wine region of Catalonia now harvest earlier in the season; the heat sweetens the grapes too early, leading to higher alcohol content, and some worry whether they’ll have to switch to dessert wines.
On an exceptionally hot day last summer, on a poultry farm, a pile of manure caught fire, as mounds of animal waste have done before. But so fierce was the wind that the embers traveled across the hills, causing fires up to 13 miles away.
Fire, Mr. Castellnou pointed out more than once, is nature’s way of reshaping the landscape for the future. What will come up on these denuded hills will be less homogeneous, he said, and more resilient for a new climate.
He favors what he calls managed burns, getting rid of low brush in order to prevent the next fire from raging out of control. And sometimes, he favors letting fires burn. It’s part of the natural ecology of the forest, he said. The white pines, for instance, reproduce only during fires, when their seed pods explode in the heat.
“Instead of fighting fire, making peace with fire,” Mr. Castellnou advised.
The only way to keep the woods from becoming dry brush by the time his two children are grown, he said, is to manage the landscape. He can see what climate change has already wrought on the hills he has lived in his whole life. The seasons are unpredictable. The heat and high winds are like nothing he has seen before.
“You can’t read the signals anymore,” he said. “You don’t know what’s going to happen next. It’s like feeling estranged at home.”
Geneva Abdul contributed reporting from London.