Galápagos tortoises may be facing a significant obstacle to their seasonal migration patterns, and some scientists are concerned.

What's happening?

The invasive species Spanish cedar was brought from mainland Latin America to the Galápagos island of Santa Cruz around 85 years ago as a fast-growing source of wood, The Wildlife Society recently explained. But researchers have found that, for reasons so far unconfirmed, tortoises tend to avoid forests made up of Spanish cedar when migrating in search of food.

"A few tortoises bludgeon their way through it," biology professor Stephen Blake of Saint Louis University told The Wildlife Society, as the animals journey around 20 kilometers (12.4 miles) each rainy season.

Despite the vast coverage of Spanish cedar forests, though, most of these creatures were found to travel through just small areas where the invasive trees were not present. "They almost invariably migrate through these little gaps through the [cedars]—these little corridors," he said.

Navigating to these more narrowly available routes could have the potential to tax the tortoises' energy and make it more difficult for them to access nutrition. 

Why is this important?

Western Santa Cruz giant tortoises are considered critically endangered by the International Union for Conservation of Nature. Spanish cedar forests hindering their ability to access the vegetation they're accustomed to seeking every year could put the species in even more jeopardy.

It's yet another example of how invasive species can disrupt the delicate balance of local ecosystems. Jeopardizing the food supply of these tortoises could cause a decline in an already dwindling population. 

The trees don't seem to have that same problem, as they can spread and overtake habitats thanks to a variety of characteristics described by The Wildlife Society: Their seeds are blown by the wind all over; they grow quickly; and they come equipped with a toxic compound to ward off pests and native plants competing for resources.

"It's quite toxic, and it's relatively insect-proof," Blake told the publication. "Native and endemic species tend not to do well in [Spanish cedar] forest."

The Centre for Agriculture and Biosciences International — or CABI — adds that the tree species "replaces native plants by blocking out sunlight with its large leaves," though the organization suggests that such shading can sometimes be a helpful attribute. CABI also notes that "dense growths of the plant are likely to increase the frequency and intensity of fires."

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What can be done about this?

Unfortunately, The Wildlife Society reported that "effective ways to remove Spanish cedar have not yet been found." 

Something else that's not yet unidentified is the exact reason why the tortoises avoid the invasive trees when migrating. It could be the toxic compound emitted by the cedars, the shade of the big leaves, or something else. 

With this still a mystery, more research — and financial support for that research — could bring us many more answers about how to support endangered animals threatened by invasive species.

Those who are concerned can get involved by supporting conservation efforts. Especially close to home, gardeners and landscapers can consciously avoid planting invasive species, which can take more effort, time, and money to cultivate anyhow. Instead, rewilding one's yard can mean a beautiful setting not only for native plants but also the creatures who thrive in and help to sustain strong, biodiverse habitats.

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