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As 2017 hurricane season ends, scientists assess tropical forest harm

  • This year’s Atlantic hurricane season – one for the record books – ended on 30 November, seeing six Category 3 to 5 storms wreaking massive destruction across the Caribbean, in the U.S. and Mexico. While damage to the built environment is fairly easy to assess, harm to conserved areas and species is more difficult to determine.
  • Satellite images show extensive damage to the 28,400-acre El Yunque National Forest in Puerto Rico, the United States’ only national tropical rainforest. However, observers on the ground say the forest is showing signs of a quick recovery.
  • More serious is harm to already stressed, endangered species with small populations. El Yunque’s Critically Endangered Puerto Rican parrot was hard hit: out of 50 endemic wild parrots, 16 are known dead. Likewise, the Endangered imperial parrot endemic to Dominica, spotted just three times since Hurricane Maria.
  • Ecosystems and species need time to recover between storms. If the intensity of hurricanes continues to increase due to escalating global warming as predicted, tropical ecosystem and species resilience may be seriously tested.
Puerto Rico’s El Yunque National Forest in 2014, before this year’s hurricanes damaged the forest canopy. Photo by HBarrison on Visualhunt.com / CC BY-NC-SA

On September 20th, the 150 mile-per-hour winds of Hurricane Maria barrelled into Puerto Rico, the worst storm to hit the island in recent history. Maria destroyed tens of thousands of homes, and, over two months later, widespread power outages still affect much of the island and hurricane-related deaths continue to rise due to a lack of access to healthcare.

A recent satellite analysis shows just how completely Maria changed the natural face of the island. El Yunque National Forest — the United States’ only national tropical rainforest — was altered almost beyond recognition, with leaves lost, branches snapped and trees downed. The transformation from lush green to barren brown is evident in remote images that capture the entire 28,400 acres of the reserve, as well as in high-resolution close-ups of smaller areas where it’s possible to pick out the fine lines of blown-down trees.

“The damage to the forest cover is significant and it no longer looks like a rainforest,” said Michelle Eversen, of the U.S. Fish and Wildlife Service’s Caribbean Ecological Services.

As climate change escalates, and the possibility of more extreme weather events increases, the danger to tropical ecosystems from record storms like those seen this year is likely to increase.

On Sept. 20, 2017 at 10:50 a.m. EDT NASA’s Terra satellite provided this visible image as Hurricane Maria moved over Puerto Rico. The eye had become obscured by clouds. Credit: NASA Goddard MODIS Rapid Response Team

Forest damage and recovery

El Yunque is one of the United States’ most diverse protected areas, home to hundreds of species of birds, animals and plants, including some found nowhere else. For example, several species of coqui frog (in the genus Eluetherodactylus), the Puerto Rican boa (Epicrates inornatus) and the epiphytic Luquillo Mountain babyboot orchid (Lepanthes eltoroensis) are endemic to the park and island.

What does it mean for these species when their habitat is transformed overnight?

For some, it’s business as usual. “It is important to remember that hurricanes are a natural part of the cycle here,” said Tana Wood, a research ecologist with the U.S. Forest Service’s International Institute of Tropical Forestry (IITF). This means that species have adapted to respond quickly after major weather disturbances.

“All [plant] species grow well after the hurricane, even those whose individuals were decapitated,” said ITTF director Ariel Lugo. “Re-sprouting is a mechanism for bouncing back and maintaining your space in the forest. Seed germination is another mechanism that favors pioneer species growing in open areas. Such species grow at unbelievable rates.”

A high-resolution close-up of a section of El Yunque National Forest. After Hurricane Maria struck, it “looked like winter had come to El Yunque,” said research ecologist Tana Wood of the U.S. Forest Service’s International Institute of Tropical Forestry. However, the forest has already started to recover, with a flush of new leaves slowly moving from lower to higher elevations. Imagery source: © 2017 DigitalGlobe. Imagery analysis: MAAP, a project of Amazon Conservation Association

“I am totally amazed at how the forest is recovering,” continued Wood. “I drove out to the forest a couple of days after Hurricane Maria and it was completely defoliated with quite a bit of structural damage (i.e. downed trees and branches, trees cut in half and twisted, etc.). It looked like winter had come to El Yunque.”

“However, within two weeks of the storm, trees started to put out new leaves, starting with the lowlands and slowly moving up the mountain. It has been fascinating to watch!”

Wood said that within a year the canopy would likely begin to close again, as trees start to put out new branches. But how long will it take for the forest to fully recover? “[W]e see the forest as continuously evolving and never returning to past states,” said Lugo, predicting a closed canopy forest would be present in 5-10 years, and a “forest without the pioneer species that regenerated after the hurricane” present in 50 years — assuming no more hurricanes hit in the meantime.

Satellite images of El Yunque National Forest, Puerto Rico, before and after Hurricane Maria caused severe damage to the forest on 20 September 2017. Leaves and branches were stripped from trees, and trees were downed, transforming the lush tropical landscape. Top panel: high-resolution imagery from Planet. Bottom panel: medium-resolution imagery from NASA/USGS. Imagery analysis: MAAP, a project of Amazon Conservation Association

At risk species heavily impacted

However, for embattled El Yunque animals already on the brink, hurricanes like Maria are especially bad news, and the possibility of recovery less sure. By 1975, the area’s endemic Puerto Rican parrot (Amazona vittata) population dropped to just thirteen individuals; since then intensive conservation efforts, including a successful captive breeding programme, have saved the species from extinction, although it is still classified as Critically Endangered by the IUCN. Before this season’s storms, a wild flock of around 50 birds was found in El Yunque’s treetops, with a slightly larger flock also present at another forest site, Rio Abajo.

Since Maria, the Puerto Rican Parrot Recovery Team has been trying to establish just how many survived. “[E]vidence collected so far indicates a significant portion of the wild population in El Yunque was lost to the storm,” Eversen said.

Only 32 were accounted for after Hurricane Irma, which struck just 3 weeks before Maria; since Maria, 16 have been confirmed dead.

The team continues to search for unaccounted parrots, and follow up on reported sightings, Eversen added. She emphasized that there was a lot of uncertainty about how many birds have been lost from El Yunque overall, but “at the current rate of recovery it could easily reach 50 percent” of the wild population. However, as Lugo pointed out, the species has been here before: “[1989 hurricane] Hugo killed a maximum of 47 percent of the parrot population,” and they recovered in the following decades.

The captive population, which numbers around 200 parrots, was kept safe during the storms. “The focus now is on repairing the aviary to be ready for the coming breeding season,” Everson said.

The Puerto Rican parrot is a Critically Endangered endemic species and the focus of intensive conservation efforts, including a successful captive breeding program. But only 32 of El Yunque’s 50-strong wild flock were accounted for after Hurricane Irma, and 16 birds have been confirmed dead since Maria. The final death toll is still not known, and all efforts are now focused on restoring the aviaries in time for the breeding season. Photo by U.S. Fish and Wildlife Service on Flickr, CC BY 2.0

Assessing natural damage across the Caribbean

Puerto Rico is just one island, and Maria just one hurricane in an annual Atlantic Hurricane Season, running June 1st to November 30th, that this year saw six hurricanes of Category 3 or above wreak widespread damage across the Caribbean and Gulf Coasts of Mexico and the United States. 2017 is likely to be among the top three most destructive seasons recorded in the region, with one preliminary damage assessment putting U.S. damage alone from just the three biggest storms at $207 billion, with another $25 billion in non-U.S. damage. Harm to the natural environment has largely not been tallied.

The Puerto Rican parrot epitomizes the most vulnerable species to hurricane harm, explained Lisa Sorenson, executive director of BirdsCaribbean, an NGO devoted to regional bird conservation. “Species of greatest conservation concern are single island or regional endemics with small population sizes, that can be wiped out in a single hurricane.”

A host of bird species found on 13 Caribbean islands fit this description, Sorenson said. That includes the Endangered imperial parrot (Amazona imperialis) endemic to Dominica — also known as the sisserou, it is the country’s national bird, and has been spotted just three times since a direct hit from Maria with sustained winds of 160 miles per hour did “mind boggling” damage to the island nation.

Also likely hard hit by the season’s storms were the Threatened forest thrush (Turdus lherminieri) found on Dominica, Montserrat, St. Lucia and Guadeloupe; the Endangered yellow-shouldered blackbird (Agelaius xanthomus); and the Endangered Puerto Rican nightjar (Antrostomus noctitherus), restricted to that island territory.

A Puerto Rican parrot aviary within the devastated landscape of El Yunque National Forest. The captive population, numbering nearly 200 birds, was kept safe during the storm, and repairs are now underway on the aviaries. Photo by the U.S. Fish and Wildlife Service, image in the public domain

“Threatened migrants to the region such as the Kirtland’s warbler (Setophaga kirtlandii) and piping plover (Charadrius melodus) are also vulnerable,” Sorenson said, along with long-legged wading birds such as the flamingo (Phoenicopterus ruber); “being such an awkward bird, it’s pretty defenseless in a storm.” Thousands of flamingos were found dead in Cuba’s northern cays after Irma’s impact.

“The greatest challenge [for birds] is in the weeks following the hurricane when food is very scarce and they have very little cover [from predators],” Sorenson said. To help with this, BirdsCaribbean is crowdfunding hurricane response efforts for affected habitats and wildlife. Long-term recovery is also challenging “because [bird species] are already under stress from so many other threats, including loss of their habitat to development, pollution, predation by invasive species, and hunting and capture for the pet trade.”

Beyond birds, Lugo sees amphibian and marine life as especially vulnerable to hurricane damage across the Caribbean. “Frogs are of concern because they are already under stress, and drought or high temperatures associated with open canopies of rain forests are a threat to their survival. Assessments of how the frogs did [this hurricane season] are in progress,” he said. “Coral reefs also suffer due to [increased] sediments in the waters as well as lowering of salinities plus mechanical effects of waves.”

A flamingo in Cuba’s northern keys, where thousands of flamingos were found dead after Irma’s landfall. Lisa Sorenson, of BirdsCaribbean, explained that long-legged waders such as flamingos are especially vulnerable to hurricanes, as they are “pretty defenseless in a storm.” Photo by Allan Hopkins on Flickr, CC BY-NC-ND 2.0

Resilient ecosystems

There has been brighter news too concerning vulnerable species that apparently weathered the storms despite the odds. On Barbuda — where 95 percent of homes were destroyed by Irma, and the entire human population evacuated — the tiny, 10-gram Barbuda warbler (Setophaga subita), restricted to the island, has clung on. “We were very worried and at first only a few birds were found, but a more intensive survey in mid-October showed that a good number have survived,” Sorenson said.

Back on U.S. soil, the season’s hurricanes forced some nationally protected areas to close, but for the most part life inside these conserved areas went on without noticeably harsh long term affects. Hurricane Harvey brought “unprecedented flooding to Southeast Texas,” said Jason Ginder, Park Ranger at Big Thicket National Preserve. But the resilience of Big Thicket’s natural ecosystem means it has “rebounded quickly,” with Harvey “leaving little long-term impacts” to habitats or species.

In Florida, Irma caused “considerable damage to trees and other vegetation throughout Everglades National Park,” as well as bringing high water levels, reported Alice Clarke, who heads up the Science Communications team at the South Florida Natural Resources Center.

The timing of the storm was fortunate for many species. “Irma occurred before the winter nesting season for most birds, including wading birds, bald eagles and osprey,” Clarke said. Subsequent surveys have found large flocks of shorebirds on nesting islands, and where nesting sites have been lost, Clarke anticipated that wading birds would continue to find suitable locations nearby.

She added that the Florida coastal tidal surge may have washed out some sea turtle nests, but because the nesting season was winding down, and turtles lay multiple clutches, “some of their clutches may have survived to hatching.”

A tiny, 10-gram Barbuda warbler. This species is just one of many that are of great conservation concern when hurricanes hit, explained Lisa Sorenson of BirdsCaribbean. Because they are endemic species with small populations, they’re susceptible to being wiped out by a single storm. But the Barbuda warbler appears to have survived against the odds, with a “good number” being recorded during surveys after Irma. Photo by Josh Noseworthy on Flickr, CC BY 2.0

Mammals have also shown resilience, with dolphin and manatee adults and calves not showing any signs of negative impacts, Clarke said. In the Florida Keys, the small population of threatened Key Deer — a diminutive subspecies of the white-tailed deer, standing just 32 inches tall, and found nowhere else — also endured Irma’s impact relatively unscathed.

As resilient as many species and ecosystems are, they still require time to recover from hurricane damage. Scientists think climate change contributed to hurricane activity and damage during the 2017 season: higher ocean temperatures fuel hurricane intensity, helping the big storms gather wind speed and collect moisture. Storms like Harvey also do more damage when they stall over one area due to changes in the Jet Stream, another more commonly seen pattern as climate change evolves. Finally, as the world warms, the atmosphere is able to contain more moisture — about 7 percent more per 1 degree Celsius (1.8 degree Fahrenheit) of warming — which helps intensify individual precipitation events.

With climate change models clearly pointing to more intense hurricanes and extreme precipitation events, nature, and especially endangered species already under stress, may find it a whole lot harder to bounce back in coming decades.

Citation:

Finer M, Olexy T (2017) United States’ only National Tropical Rainforest ravaged by Hurricane Maria (Puerto Rico). MAAP: 73

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