Image credit: KhayaL/Flickr
They are iconic symbols of the tropics but coconut palms are, in fact, an introduced species in the Pacific islands. It's not known whether the first trees found root after coconuts floated from their native Asia or whether they were transplanted by the first human settlers, but either way, they have had a powerful effect on the ecosystems of their new homes.
In fact, recent research is showing that coconut palms are the starting point for a chain of ecologically damaging changes.
Seabirds avoid the trees, choosing to nest in other places instead. When the birds leave an area so does their guano—an important fertilizer for tropical soil. Hillary Young, a member of a Stanford University research team studying ecology of the Palmyra Atoll in the South Pacific, explained:
We found that you can get a five- to twelvefold decline in important soil nutrients such as nitrate and phosphate when coconut palms are present, mainly because the birds aren't there depositing nutrients to that system.
Typically, she explained, introduced plants enrich the nutrient content of their new ecosystems. Young added that "this is an unusual example of an introduced or spreading plant that causes wide nutrient declines in ecosystems."
Coconut palms are spreading rapidly in the region, researchers say, mostly due to conscious planting meant to encourage development. People like the plants because they provide shade, food, and raw materials for making rope and other essentials. Though the palms attract people, they have the opposite effect on other plants and animals.
Young commented that "whenever coconuts are present, the nutrient levels decline in the leaves of each species...coconut palms don't increase nutrient levels of anything." Researchers wondered, however, whether nutrient depletion had a greater effect.
Conducting a Taste Test
To test this, they placed leaves of the same species of plant in a bucket with a crab. One of the leaves was sourced from a forest with coconut palms, the other from a forest without them.
The results, they reported, were surprising. To a dramatic degree, animals in the taste tests chose the leaves from native forests, indicating a highly-tuned ability to select for greater nutrient content.
Young explained that:
An apparently innocuous change to...plant communities can disrupt invisible connections among ecosystems and potentially trigger a cascade of change that can fundamentally alter those ecosystems.
She concluded that "the emphasis needs to be on protecting native plant communities and preventing damaging disruptions from happening in the first place."