The Night the Forest Lost Its Leaves

Early on September 20, 2017, Hurricane Maria roared into Puerto Rico. It came ashore near the town of Yabucoa as a Category 4 storm, with winds of about 155 miles per hour. (A hurricane's category, 1 to 5, tells you how strong its winds are. Category 4 is very strong.) The wind tore across El Yunque, the rainforest in the Luquillo Mountains. In just a few hours, it ripped the leaves off the trees.

Before sunrise on September 20, 2017, Hurricane Maria made landfall near Yabucoa, Puerto Rico, as a Category 4 hurricane with maximum sustained winds of roughly 155 miles per hour. (A hurricane's category, on a scale of 1 to 5, measures how fast its winds blow; Category 4 means extremely dangerous winds.) Those winds swept over El Yunque, the tropical rainforest in the Luquillo Mountains on the island's northeast. In a matter of hours, Maria stripped the forest's leaves and snapped its branches, beginning one of the most dramatic single days in the forest's modern history.

When the storm passed, the green rainforest was gone. The leaves had been torn away, leaving bare, broken trees. Scientists described the land as a muddy stretch of leafless trees. They even said Maria gave the forest "a haircut." Using lasers from the sky to measure the trees, researchers found the forest had lost about 23 feet of height on average. That is like the top of the forest sliding down two stories.

When Maria moved on, the lush green canopy was simply gone. The storm had turned a closed rainforest into a muddy expanse of leafless trees, and scientists said it had given El Yunque "a haircut." Using lidar (laser scanners flown overhead that measure the height of the treetops), researchers found that the forest lost about 23 feet, or 7 meters, of canopy height on average. Across the study area, 73 percent of the forest lost at least a meter of height. Compared with earlier storms like Hurricane Hugo, Maria doubled the number of trees that died and tripled the number of broken trunks.

The canopy is the leafy roof at the top of the forest. It keeps the forest floor cool and shady. When Maria tore it away, sunlight suddenly flooded the ground. Scientists said the rainforest looked more like an open, sunny woodland than a shady jungle. The canopy is also where many animals live. Birds and tree frogs called coquíes find food and shelter in those leaves. When the leaves vanish, their home does too.

The canopy, the leafy roof formed by the tallest trees, is the heart of a rainforest. It shades the floor, holds in moisture, and feeds and shelters wildlife. When Maria peeled it away, sunlight poured straight to the ground, and scientists said El Yunque suddenly resembled an open savannah woodland instead of a dim, dripping jungle. That matters because the canopy is a living pantry and apartment building. El Yunque shelters 97 bird species and 13 of Puerto Rico's 17 coquí frog species, many of which depend on leaves, fruit, and tangled branches for food and cover. Strip the leaves, and you strip their world.

Here is what makes Maria so unusual. Some forest dangers are slow. Far away in Washington State, the Hoh rainforest is losing its mountain ice little by little over many years. El Yunque's biggest danger is fast: a hurricane can change everything in one morning. Long ago, a really big hurricane hit about once every 50 years. But El Yunque has now had three powerful ones in just 30 years.

What makes Maria so striking is its speed. Many climate threats unfold slowly. In Washington State's Hoh rainforest, the danger is the gradual loss of mountain ice over decades. El Yunque's defining threat is the opposite: acute and sudden, a hurricane that rewrites the forest in a single morning. And these storms appear to be coming more often. Scientists note that a major hurricane once struck roughly every 50 years, yet in the past 30 years El Yunque has weathered three major (Category 3 or stronger) hurricanes, a pace researchers say may preview the warmer, stormier future ahead.