Ecologists Can’t Beat Invasive Species, So They’re Joining Them

T

he path to Ohe’o Gulch, in Maui, meanders through a short section of forest, past mango trees and pockets of bamboo, then opens onto the ocean. Palm trees of all sizes and varieties line the Pacific coast, their trunks hunched over the sand, fronds waving picturesquely in the trade winds.

Though they may seem perfectly at home, iconic to the landscape, most of these trees are outsiders. They hitched a ride long ago, with the Polynesians or Europeans, and not innocuously; they’ve been crowding out the native palm species that belong to the genus Pritchardia—in some cases, almost to the point of extinction. Which raises the question: Should ecologists care that the trees who were here first are being ousted, and do something to stop and reverse it? The ethical— or ideological—quandary is familiar to art conservationists, who argue how best to preserve a masterpiece: by letting its paint gracefully bear the effects of aging, or preventing them altogether to retain the work’s initial appearance.

“For a long time,” said Donald Drake, a botanist and conservation biologist at the University of Hawaii, “one of the main strategies of conservation has been restoration: You take a place that’s been messed up, disturbed by people, and you try and put it back to what it was like 100 years ago, or before Europeans came. In a lot of places that’s just not realistic. We need to come to terms with things that are never going back.”

One way to do that is to embrace the idea of “novel ecosystems”—hybrid environments that combine native and nonnative species (the latter includes anything that was transported by humans). They cover much of the Hawaiian Islands, America’s “endangered species capital.” It’s home to 366 plant taxa and 30 bird taxa listed as threatened or endangered, and remedies are hard to come by. The strategies that have been used to successfully restore or preserve fragile environments in other parts of the world, like planting native tree species to rebuild rain forests in Costa Rica, are often ineffectual in Hawaii due to the high number and tenacious grasp of invasive plants, which rapidly crowd out natives and negatively impact the ecosystem (nonnatives are more peaceful cohabiters).

Few researchers know the trials of combatting invasive species better than botanists Susan Cordell and Becky Ostertag, who just published a “sobering” report of their decade-long battle against invasives on the Big Island. The experience seems to have been emotionally taxing; the tone in the study’s abstract isn’t disinterested or detached. “We were disappointed and perhaps discouraged in our results—little recovery of native biodiversity despite ongoing and labor-intensive management,” they, along with colleagues, wrote in Restoration Ecology. Not only did they fail to return the rule of the forest to the native species, their efforts backfired—more new species invaded. This “setback” against the invaders, they wrote, prompted them to reflect and eventually adopt a new philosophy: “join them.”

Another way to put it, says botanist Chuck Chimera, is that “the Puritanical types might consider [the idea of novel ecosystems] heretical.” 

“Our hypothesis is the complementary traits (of native and nonnative plants) would be more effective at reducing invasions,” Cordell said. Nonnative plants, in their current experiment, will now be allowed to mingle with the Hawaiian natives. The outsiders will be chosen specifically to create “functional diversity”—they’ll promote the growth of native species and the overall health of the forest, providing food and habitats for native wildlife, while also keeping harmful invasive species out. Ultimately, the goal is to have a select number of nonnatives work together with the native plants to prevent the really destructive invasives from running amok.

This experiment began in January 2014 and involves monitoring 20 different plots of land, four left untouched and 16 that were first cleared of all invasives then filled with a mixture of native and nonnative plants. For the next five to ten years, the scientists will monitor the amount of time spent weeding, plant production rates, tree litter, and a number of other metrics to gauge how well the native and nonnative species are working together to produce an ecosystem that recycles nutrients, provides habitat and food for native birds, and pulls carbon from the atmosphere. Eventually Cordell and Ostertag would like to create ecosystems that manage themselves without the need of human intervention; no more weeding to keep out invasive plants, no more worrying about the mono-dominance of a particular species—dangerous for many of the same reasons that mono-cropping is a gamble in agriculture (a pest or disease can easily wipe the species out, and less diversity means more chance for soil nutrients, or other aspects of the ecosystem, falling out of balance).

Despite how both Cordell and Ostertag began their careers—wanting to save every threatened plant—both have adjusted their goals. “Conservation and preservation is a crisis discipline, and it needs to be pragmatic,” Ostertag said. “Given how limited resources are, in terms of money and labor and time, it just doesn’t make sense to put a huge amount of energy into some ideal that can’t be maintained.”

Not everyone’s sympathetic to this resignation. A 2014 paper, “A critique of the ‘novel ecosystems concept,’” in Trends in Ecology & Evolution, argued that the idea is ill-defined and could undermine support for restoration projects. Another way to put it, says botanist Chuck Chimera, a member of the Hawaiian Invasive Species Council’s Weed Risk Assessment team, is that “the Puritanical types might consider [the idea of novel ecosystems] heretical.” He’s seen his fair share of invasive species gain power in the islands’ fragile ecosystems. Every time a species is threatened, it feels like a personal blow. He knows that any hope—even joining forces with the enemy—is better than nothing.

The environment here, he said, is like a “living library of the biological, evolutionary, and cultural history of Hawaii. If you went into a library of 60,000 books and pulled out 100, would you notice? Maybe not. But what if you pulled out the most elaborate, beautifully illustrated, large-color picture book and said that one’s no longer part of the library? Then people would start to take notice.”

Lorraine Boissoneault writes about science, nature, history, and adventure. Her book The Last Voyageurs was published in 2016. Follow her on Twitter @boissolm.

This article previously appeared in Nautilus.