They’re way too easy to find on the inhabited islands of the Galápagos. Raspberries, guavas, orange cestrum–introduced plants, crowding out native plant species with potentially disastrous effects to fragile island ecosystems.
Now a new scientific study published in the online journal Neobiota maps the extent of the invasion on Santa Cruz Island, finding that almost half of the island’s humid highlands are covered non-native trees, shurbs and grasses from other parts of the world.
“People may be shocked that a place considered so iconic for biodiversity is so overrun with weeds in some areas, but this really is a global story,” lead researcher Mandy Trueman of the University of Western Australia said on the university’s website.
The study mapped a 35,000 acre area (14,214 hectares), documenting the plant invasion through satellite images and observations on the ground. The number one invader was Spanish cedar (Cedrela odorata), covering almost 2,150 acres. Common guava (Psidium guajava) came in second at 1,920 acres. Orange Cestrum (Cestrum auriculatum) came in third at almost 1,350 acres.
“These invaders compete with native plants for light and water and can change the environment so that both flora and fauna are affected,” Trueman said. “These invasions are one of the factors threatening Galápagos species, many of which occur nowhere else in the world.”
The study was a joint effort by a team of researchers from the Charles Darwin Foundation, Galápagos National Park and the University of Western Australia. The researchers hope their findings will guide Galápagos officials in developing programs to scale back the plant invasion in places like the Santa Cruz highlands.
“There are still a lot of native species present,” Trueman said, “And I hope this study can help managers decide where to take action to protect our precious native flora and fauna.”
Trueman, a doctoral candidate at the University of Western Australia, lived on Santa Cruz from 2008 until earlier this year.