Local researchers agreed the largest threat to native Hawaiian forests is the invasive strawberry guava tree. Of the various tactics they suggest in fighting it, the most common one is to eat it.
“The worst invasive species in the state as far as plants go is strawberry guava,” said Dr. David Bybee, the Associate Academic vice president for Instruction at BYU–Hawaii. “It comes in and chokes out the native forest.”
Kapua Kawelo, Natural Resource manager for the U.S. Army Garrison in Hawaii, said, “Strawberry guava is well established in our islands, unfortunately. It takes over areas and forms monotypic stands. It can give off chemicals and change the environment so nothing else can grow.”
As a result, Kawelo continued, native forests are slowly being overrun by strawberry guava. She added, “Feral pigs and guava go hand in hand. Volunteer and private hunters are vital in keeping guava from spreading.”
Bybee, who is a marine biologist and also an environmental consultant, explained how the pigs help spread strawberry guava. “Pigs will eat the guava and then run up into the hills and spread the seeds up into higher elevations, so the guava will climb up the mountains.”
All major conservation groups on the island, including the Oahu Army Natural Resource Program (OANRP), are constantly working in a massive effort to contain the spreading of strawberry guava.
Invested students can volunteer, they said, or at the most basic level of activism, eat local pork and harvest the strawberry guava to prevent further spreading.
Strawberry guava is recognizable by its reddish bark, short rounded stiff dark green waxy leaves, and distinct small red fruit growing in clumps on the end of branches.
Invasive species: The biggest threat to native Hawaiian ecosystems
“We are the endangered species capital of the country and the highest in the world possibly,” said Bybee. “We’re so isolated that this place is a treasure trove of endemic species, species that are only found here, that didn’t develop defenses.”
According to Kawelo, “Hawaii has a unique natural history and organisms didn’t get established here but every 10,000 years via birds, wind, and water. Humans started bringing species and the native species weren’t used to that rate of introduction and got out-competed.”
Bybee continued, “The landscape has become so changed by invasive species that ancient Hawaiians wouldn’t recognize the jungle today. You walk up the Laie Falls Trail, and you won’t see a native plant. You’d have to go about a mile past the falls to see that.
“Strawberry guava is originally from Brazil, and over there it has its niche, but out here there’s nothing to contain it.”
When asked why fighting invasive species is important, Kawelo replied, “The plants and animals of Hawaii are what makes Hawaii unique and defining for native Hawaiians. They were here when Hawaiians arrived and we’ve used them for native purposes. They’re what makes Hawaiian unique. That’s reason enough.
“If we lose the plants and animals, we lose their stories and won’t be able to relate the value of them to their kids. People come here to see the species that are found nowhere else in the world. We’ve been part of the change in bringing these species here, and now we need to be part of the solution in preserving native species.”
Bybee explained invasive species often affect all aspects of a native environment.
“Invasive species don’t allow natural ecosystems to function very well. For example, [in Hawaii] native plants act as a sponge and keep the water in the ecosystem longer instead of rushing into the ocean so it has time to percolate down. In this way, native species prevents runoffs that keep soil from choking out coral reefs, which in turn help fisherman get better fish.”
Jane Contrell, a freshman majoring in psychology from Utah, said, “We need to preserve native species. Most of the people who live here [Hawaii], it isn’t there home, [and] they don’t appreciate the place they live in. I feel they’re taking advantage of it because ‘it’s paradise’ or ‘it’s not my responsibility’ so why does it matter?
“But I want to respect Hawaii, and even though I haven’t done a lot [to fight invasive species], I want to become more involved,” through volunteering with local conservation groups Contrell explained.
Efforts in controlling strawberry guava
“There are other weeds that aren’t established and the goal there is elimination,” Kawelo explained. However, with strawberry guava, “we pick and choose areas where to control it since it’s everywhere.
“We’re trying to restore the habitat within the Waianae and Koa’loa areas. We’ll go in and cut them down or treat them with herbicide. We can pretty much kill all the guava in the Koa’loa, but in the Waianae, we have to do the removal and it’s much harder.
“We use the Ecosystem Restoration Team, and its goal is to connect patches of native vegetation by removing guava within a specific area. They’ll clear cut guava patches and chip them up occasionally to keep down other weeds and help with seeding. They’ll then sow native species including mamaki, which is one of the first successional plants.” Mamaki is a small medicinal tree often used to make teas with distinct slender green leaves growing to almost a foot long with red veins.
Kawelo continued, “We’ll then add patches of koa [tree] seedlings. Those are the first tier trying to re-establish canopy. Once that’s in the ground, we will plant understory species that are appropriate to the site we’re working, i.e ferns, uki-uki, shrubs - whatever we can collect successfully from the area.
“It’s been really successful. We’re actually seeing germination of endangered species that allow for the habitat of native species. We’ve transformed it from 100 percent strawberry guava to native habitats where endangered species can grow,” in both the Waianae and Koa’loa areas.
Anyone interested in more information on fighting strawberry guava can contact the OANRP by clicking here.
Writer: J. Eston Dunn