(CN) – Besides the devastation to human life, 2017’s Hurricane Maria wreaked surprising havoc on Puerto Rico’s forests – something that could be the norm in the Atlantic tropics due to a warming climate, scientists warned in a new study published Monday.
Titled "Hurricane Maria Tripled Stem Breaks and Doubled Tree Mortality Relative to Other Major Storms,” the study published in Nature Communications shows damage to trees in Puerto Rico by Hurricane Maria was unprecedented in modern times. Because hurricanes are projected to intensify as the climate warms, the damage from Hurricane Maria is a likely indicator of more damage to old growth forests, according to lead author Maria Uriarte of Columbia University's Earth Institute.
Hurricane Maria not only destroyed far more trees than any previously studied storm, it took down big, old trees thought to be more resistant to storms. Greater tree damage impacts biodiversity and adds more carbon to the atmosphere, the study authors say.
"These hurricanes are going to kill more trees. They're going to break more trees. The factors that protected many trees in the past will no longer apply," Uriarte said. "Forests will become shorter and smaller, because they won't have time to regrow, and they will be less diverse."
Hurricane Maria hit Puerto Rico in October 2017 as a Category 4 hurricane, packing winds of up to 155 miles per hour and dumping as much as three feet of rain in some areas. An estimated 20 to 40 million trees were damaged or killed when they were stripped of foliage, snapped in half or ripped from the ground in the strongest storm to hit the island since 1928.
Uriarte had been monitoring tree growth and mortality across Puerto Rico for more than 15 years when the hurricane hit. She and two colleagues focused on documenting damage in a 40-acre section of the El Yunque National Forest, near the capital of San Juan, that has been intensively monitored by multiple teams since 1990. This long-term monitoring allowed researchers to compare damage from Maria with that of past hurricanes, including two Category 3 storms – Hurricane Hugo in 1989 and 1998's Hurricane Georges.
The comparison showed Hurricane Maria killed twice as many trees outright as previous storms, and broke more than three times as many trunks. Shockingly, the slowest-growing and most valuable hardwoods that had survived past storms are now dead or damaged, with the damaged trees expected to die in two to three years. These include species that provide habitat for a variety of bird species, towering mahogany-like tabonucos with great crowns prized for furniture and boat-building, and thick ausubos, with wood so dense it does not float in water.
Uriarte and her colleagues noted that one species – the common sierra palm – weathered the storm and may take over future forests. The species of palm tree features a slender, flexible trunk that bends with the wind and quickly resprouts, grass-like, from its top when it loses foliage.
"This will yield lower statured and less diverse forests dominated by a few resistant species," she said.
These and a few pioneer species that can take root quickly and grow following storms may be the future of forests across the Atlantic tropics and subtropics, according to Uriarte.
Along with palms, the fast-growing yagrumo is another species that researchers say would probably take over and create additional problems. While the yagrumo shoots up quickly in sunny clearings created by big storms, it is often the first to fall in storms – adding to the already decaying trees felled by previous storms.
Along with changing the makeup of the forests wildlife and plant species that were previously dependent on old growth habitat the decaying plant matter would help feed the warming that is creating bigger storms and destroying habitat. The replacement forest species will not be able to soak up enough carbon to make a difference.
According to separate estimates, trees killed or damaged by Hurricane Maria alone will release about 5.75 million tons of carbon to the atmosphere – roughly 2.5 percent of the carbon taken up annually by all forests in the United States. Other scientists in the same field as Uriarte are recognizing the importance of her study to help predict the overall climate change impacts.
Edmund Tanner, a senior lecturer emeritus at the University of Cambridge who also studies tropical trees, said Uriarte’s study is important because it reports different, rather than just intensified, effects of strong versus weaker hurricanes.
“[The effects are] probably representative of huge areas of tropical lowland forest near sea coasts, some of which are likely to experience similar or worse damage in a warming world," Tanner said.
Scientific models show rising Atlantic temperatures will boost maximum sustained hurricane winds by 15 percent by 2100. Ocean heat energizes tropical cyclones and warmer air carries more moisture, which could lead to a 20 percent increase in rainfall near storm centers. Both wind and rain destroy trees: Extreme winds destroy directly while rain saturates and destabilizes soil, resulting in uprooting.
Tanner noted Maria was a Category 4 hurricane.
"There is a Category 5," he said.
Jill Thompson, a plant ecologist at the Centre for Ecology & Hydrology in the United Kingdom, and Jess K. Zimmerman, a professor at the University of Puerto Rico in San Juan co-authored the study funded by the U.S. National Science Foundation.
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