Two years after hurricanes Irma and Maria ripped through the islands, optimistic nature lovers are quick to point out signs of recovery – sea grape trees are once more putting out fruit; at least one species of humming birds is frequenting bird feeders; and snorkelers can find spots where schools of fish thrive and sea fans wave in the currents.
Biologists, however, are much more reluctant to celebrate nature’s recovery. Although plants and creatures – especially those species native to the islands – have evolved to withstand the devastation of major hurricanes, scientists say recovery is a matter of decades, not of years.
This is the first story in this Irmaria anniversary series about the recovery of natural phenomena – vegetation, marine life, and wildlife.
Shorelines bear the brunt of the storm
“Even without another major storm, the effects of hurricane Irma will be visible for the next 50 to 60 years, particularly at coastal areas,” said Eleanor Gibney, a specialist in native species.
Gibney has only to look at her own front yard, which extends right up to the sandy beach at Hawksnest Bay on St. John, to see the damage.
“There’s some natural regeneration, but the line of vegetation has moved way back,” she said.
What used to be soil is now several inches of sand. Gibney is busy propagating buttonwood and sea grape trees to plant along the beaches on the north shore of St. John in the hope of stabilizing shorelines.
The devastation of Irma was perhaps not unprecedented. Gibney has a photo of her yard taken sometime between 1905 and 1912 when John Lindquist owned the property.
“In that photo there’s one large almond tree that’s still there, but there are no other trees along the shoreline more than five years old,” said Gibney.
This indicates that the lush screen of almond trees and sea grapes that until 2017 grew along the shore was only about a century old when it was destroyed by Hurricane Irma. Coconut palms planted by Lindquist in the early 20th century were already almost all gone, but dozens of palms planted by the Gibneys in the 1950s-1970s were lost in Irma. Sand deposits in Gibney’s yard far from the shore are further confirmation that a storm on Irma’s track may have changed the north shore coastline dramatically back then.
In some coastal areas, such as along the road to Annaberg in the Virgin Islands National Park, trees like pond apple, beach maho and manchineel are coming back with a vengeance.
Manchineel could prove to be a problem for park resource managers as the trees are toxic to humans. The bark and leaves can give people a nasty rash, and the apple-like fruits can be fatal if ingested.
“Like a lot of native plants, these are trees that have life cycles well adapted to hurricanes. The big manchineel trees died immediately with the hurricane,” said Gibney, “but their seeds last for decades, and with all the sunlight pouring in, they’re all growing.”
Mangrove swamps are beginning to recover
The manchineel trees and pond apples bordering the mangrove swamp along the roadside near Annaberg are deceptive. Park visitors might mistake these species for regrowth of the mangroves which were devastated when the high winds of Irma tore the leaves off the trees.
Since the storms, passers-by are sometimes alarmed by a stark snaggle of bare branches that emerge from basins where lush mangroves once grew. However, mangroves are uniquely equipped to regenerate, according to ecologist Gary Ray.
“Salinity is a constant, so red mangroves are adapted to that. They need to run ‘metabolic pumps’ to exclude the salt and sequester it in the leaves. Sunlight runs the system to operate the pumps. However, if a hurricane blows all the leaves off, there’s no energy coming into the plants, so all the trees in the basin die of both lack of oxygen to the roots and salt toxicity.”
However, the whole mangrove community is adapted to recover from that, Ray explained.
“Red mangrove trees produce specialized seeds that germinate while remaining attached to the branches. Hurricane winds rip these seedlings from the trees, and they drop into the pond muck below. It is these seedlings that represent the next generation of red mangroves.
“When you look at mangrove swamps, they’re evenly aged. You might see trees that have grown up since Hurricane Hugo that are now almost 30 years old. They’re all the same size because they all grew as a single cohort, regenerating in the same post-hurricane year.”
When mangrove trees reach a threshold height of about 10 feet, Ray said termites will once again move in and build their nests in the living trees; from there, the termites will continue to play their role in hastening the decomposition of the dead wood, continuing to provide nutrients to further the regeneration of the mangroves. Red mangroves can reach a height of 30 feet if they’re not destroyed by a storm.
There is greater concern for the red mangroves fringing Hurricane Hole on St John’s east end, according to Gibney. The combination of the past 20 year’s explosion of the non-native deer population browsing these seedlings, and the effects of the hurricane surge and surf have led to a concerning lack of regrowth on this critical shoreline.
Recovery of the dry forest
Termites play a critical role in the dry forest as well, according to Ray. After Hurricane Hugo in 1989, more termite nests remained because fewer trees went down than during Irma and Maria in 2017.
“Arboreal termites are very important to the dry forest. Without them, and the specialized bacteria residing in the termite gut, there would be a major loss in decomposition, which would interfere with the functioning of the forest,” said Ray. The presence of fungi and bacteria in the soil are also essential to the recycling of nutrients that make plants grow.
The 2017 hurricane season affected the dry forests in another way.
“Hurricane Irma wiped out more of the forest canopy probably more than anything on record. It significantly disrupted the ground layer and sub-canopy. There’s no protection from rapidly fluctuating levels of humidity and infrared radiation – sunlight,” said Ray.
Each organism has a fundamental environmental tolerance range, thriving or dying depending on the amount of moisture, heat, and light, Ray explained. The change in conditions from the loss of the canopy has altered all of this. “There are hundreds of species in our forests, all competing for similar resources. Plants have to grow next to each other; sometimes one species grows at the expense of other species,” he said.
Other factors lead to regeneration. “St. John is 80 to 90 percent forested, and the roots systems are left largely intact, except where trees topple over during a hurricane. Much of the plants’ energies go into re-sprouting which starts right away with the rains that follow a hurricane.”
The extreme winds of Hurricane Irma snapped tree limbs and broke trunks, but native species have all evolved in landscapes with hurricanes for hundreds of thousands, if not millions of years, according to Ray. Lower tree heights are a factor in fewer “tip ups” – trees that were toppled with their roots sticking up.
“In Puerto Rico, on wet rain forest slopes, a very tall tree will tip up and crush a lot of other trees as it falls,” said Ray. “Here in the Virgin Islands, the trees fracture, then re-sprout new branches, and the termites and fungi are ready to consume the woody litter on the forest floor. Decomposition goes crazy. In five to 10 years, most of the fallen wood becomes part of the soil.”
Until that process has evolved a bit further, anyone walking through forested areas will need to stay on cleared trails.
An expert in “bushwacking,” Gibney was accustomed to going off the trails to conduct her research on native species, but she says it’s now too difficult because of the number of broken trees and the subsequent growth of opportunistic plants like tan-tan and prickly catch-and-keep. “You just can’t get through,” she said.