Restoring Palmyra's Rainforest

By Gina Lobaco

Conjure an image of a remote tropical island, and chances are a swaying palm tree appears in your mind’s eye. Yet for most of the coral cays in the Pacific and Indian Oceans, coconut palms are a late arrival, introduced as a “canoe crop” by ancient voyagers on their ocean crossings.

Instead, tropical cays were once thought to shelter abundant forests of Pisonia grandis, a native species much in decline in the modern world. At Palmyra Atoll, one of the last large stands of this ancient tree used to dominate the atoll’s native rainforest, but the introduction of competitive coconut palms and hungry rats, coupled with deforestation related to U.S. military activity during WWII, reduced Palmyra’s Pisonia forest to a few patches.

Rats were successfully removed from Palmyra in 2011, and since then Pisonia seedlings have been on the upswing—as have the coconut palms, which were originally introduced to harvest copra as a cash crop but are now invasive. To improve Pisonia’s survival rate, Palmyra program director Dr. Alex Wegmann plans to remove many of the palms and replace them with Pisonia and other native canopy species. His goal: to reestablish Palmyra’s native rainforest.

An Anchor Tree

A flowering evergreen with soft porous wood belonging to the bougainvillea family, Pisonia grandis can reach heights of nearly 80 feet—an astounding altitude, considering its shallow root system develops in the extremely low elevation of a coral reef atoll. In the Maldives, its tender leaves are used as a spinach-like “stew pot” vegetable, and elsewhere it is a folk remedy for dysentery.  More recently, researchers have begun extracting pinitol, an anti-diabetic agent, from its leaves.  

Pisonia grandis was once an important player in island ecosystems, with a spreading canopy that provides comfortable nesting sites for migrating seabirds. Yet even on remote, uninhabited Palmyra, its dominance was challenged.

First, the U.S. Navy leveled many of Palmyra’s islets during World War II to build a refueling station. In the process, Pisonia was all but eliminated from Cooper Island, the atoll’s largest land mass and today a Nature Conservancy preserve.

Second, the Navy fleet and previous visiting vessels brought an invasive rat species that ate the tender shoots of young plants. The introduction of coconut palms further crowded out Pisonia by preventing sunlight from reaching saplings on the forest floor. Unlike Pisonia, coconut palms are inhospitable nesting spots for Palmyra’s large colonies of seabirds, among them Red-footed Boobies and Black Noddies.  

Replanting the Forest

To reestablish Palmyra’s pre-WWII native forest, Wegmann plans to collect phytoliths—minuscule silica structures from decayed plant tissue—and pollen from sediment samples to understand the natural distribution and abundance of Palmyra’s native tree species. Next, invasive coconuts will be strategically removed and replaced with Pisonia and other trees that benefit Palmyra’s native ecosystem.

Wegmann is already encouraged by a few flourishing specimens he has planted on Cooper Island. But he’ll have some help in the reforestation project: once the trees establish themselves, the birds that nest in their branches enrich the soil with guano. For Pisonia, they become the unwitting agent of the tree’s reproductive cycle by dispersing the plant’s small, sticky seeds, carried in their feathers to other remote atolls and islands across the Pacific.

“Restoring Palmyra’s rainforest began with the eradication of invasive rats. Reestablishing the native tree canopy is our next move to protect this incredible ecosystem,” Wegmann says. “Trees grow so fast in Palmyra’s warm, wet climate—we will have a mature, 40-foot canopy within 10 years of planting the first seedling.”    

 

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