canopy

5 Things: How Hurricanes Have Changed Puerto Rico’s Forests

In September 2017, Hurricanes Irma and Maria hit Puerto Rico, knocking out critical infrastructure and ransacking the island’s forests. In April and May 2018, a team of our scientists took to the air to take three-dimensional images of Puerto Rico’s forests using Goddard’s Lidar, Hyperspectral, and Thermal Imager (G-LIHT), which uses light in the form of a pulsed laser. By comparing images of the same forests taken by the team before and after the storm, scientists will be able to use those data to study how hurricanes change these important ecosystems.

Here are five ways scientists say the hurricanes have changed Puerto Rico’s forests since making landfall eight months ago:

1. The Canopy Is Bare

One word defines the post-hurricane forest canopy in El Yunque National Forest: Open.

“The trees have been stripped clean,” said NASA Goddard Earth scientist and G-LiHT co-investigator Doug Morton. He was there a year ago, months before the hurricanes would ravage the area. When he returned to the forest in April 2018 to gather measurements of trees on the ground to complement the airborne campaign’s lidar work, he could now see from the mountainside downtown San Juan, which is 45-minutes away by car.

And no canopy means no shade. “Where once maybe a few flecks of sunlight reached the forest floor, now the ground is saturated in light,” Morton said, adding that such a change could have profound consequences for the overall forest ecosystem. For example, some tree seedlings that thrive on a cool forest floor may whither now that daytime temperatures are as much as 4 degrees Celsius (7 degrees Fahrenheit) hotter than they were before the hurricane. Meanwhile, as we shall see, other plants and animals stand to benefit from such changes.

“Who are the winners and losers in this post-hurricane forest ecosystem, and how will that play out in the long run? Those are two of the key questions,” said Morton.

2. Palms Are on the Rise

One species that’s basking in all that sunlight is the Sierra Palm, said Maria Uriarte, a professor of ecology at Columbia University who has researched El Yunque National Forest for 15 years. “Before, the palms were squeezed in with the other trees in the canopy and fighting for sunlight, and now they’re up there mostly by themselves,” she said. “They’re fruiting like crazy right now.”

The secret to their survival: Biomechanics.

“The palm generally doesn’t break because it’s got a flexible stem—it’s got so much play,” Uriarte said. “For the most part, during a storm it sways back and forth and loses its fronds and has a bad hair day and then it’s back to normal.” By contrast, neighboring trees with very dense, strong wood, like the Tabonuco, were snapped in half or completely uprooted by the force of the hurricane winds.

“Palm trees are going to be a major component of the canopy of this forest for the next decade or so,” added Doug Morton. “They’ll help to facilitate recovery by providing some shade and protection as well as structure for both flora and fauna.”

3. Vines Are Creeping Opportunists

Rising noticeably from the post-Hurricane forest floor of El Yunque National Forest are woody vines called lianas. Rooted in the ground, their goal, Morton says, is to climb onto host trees and compete for sunlight at the top. That, combined with the fact that their weight tends to slow tree productivity potential, means they are literally a drag on the forest canopy. As lianas can wind their way around several trees, regions with more of these vines tend to have larger groupings of trees that get pulled down together.

“There’s some indication that vines may be more competitive in a warmer, drier, and more carbon dioxide-rich world,” Morton said. “That’s a hypothesis we’re interested in exploring.”

4. Endangered Parrot Populations Have Taken a Hit

The endangered Iguaca is the last living native parrot species of Puerto Rico. The island’s two Iguaca aviaries have reported a substantial number of deaths in the wild due to the hurricanes. In the forests of Río Abajo, in western central Puerto Rico, about 100 of the roughly 140 wild parrots survived; in El Yunque National Forest in the eastern part of the island, only three of the 53 to 56 wild parrots are known to have pulled through.

“It was a huge blow,” said the U.S. Fish and Wildlife Service’s Tom White, a parrot biologist stationed at the aviary in El Yunque, which took the brunt of Hurricane Maria’s Category 5 winds. Some of the parrots died from injuries received during the storm, while others likely died from increased predation from hawks because there were no longer canopies for them to hide in. The rest succumbed to starvation. The Iguaca subsists on flowers, fruits, seeds, and leaves derived from more than 60 species—but for several months following the storm, the forest was completely defoliated.

Despite the setback, White said he’s optimistic that the Iguaca will rebound. In Río Abajo, the number of wild Iguaca are enough that they should rebound on their own; in El Yunque there are about 227 birds at the aviary—a strong number for continued breeding and eventual release into the forest once conditions improve enough. “One of their main fruit comes from the sierra palm, and they’re now flowering and starting to produce again,” White noted. “It’s probably going to take about another year for things to level out, but the forest is gritty.”

5. Lizards and Frogs: A Mixed Response

When Hurricane Maria stripped the leaves off of trees, changes in the forest microclimate instantly transformed the living conditions for lizards and frogs. Species have reacted differently to the event based on the conditions they are adapted to, said herpetologist Neftali Ríos-López, an associate professor at the University of Puerto Rico-Humacao Campus.

For example, some lizard species are naturally suited to the forest canopy, which is warmer and drier. “After the hurricane, those conditions, which were once exclusive to the canopy, have now been extended down to the forest floor,” Ríos-Lopez said. “As a result, these lizards start displacing and substituting animals that were adapted to the once cooler conditions on the forest floor.”

Likewise, among frog species the red-eyed coquí, with its resistance to temperature and humidity fluctuations and its ability to handle dehydration better than other coquí species, has benefited from the warmer, drier conditions in the forests after the storm. Traditionally a grassland species, they are expanding from the lowlands to the mid- and even high parts of the mountains, Ríos-Lopez said. “Physiologically, what was a disadvantage for that species when the whole island was forested now finds itself in a positive position.” Conversely, forest-acclimated coquí frog species have declined.

That said, as the forests recover, so will many of the species whose numbers have dwindled following the storms. “It will take many years, decades, I would guess,” Ríos-Lopez said.

Our scientists are working with partners from universities and government to use G-LiHT airborne data to inform ground research on forest and other ecosystems not only in Puerto Rico but also throughout the world. To follow their campaigns and keep up with the latest news, find them here: https://gliht.gsfc.nasa.gov.

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