invasion curve — Maui Invasive Species Committee (MISC)

_{Bingabing is an invasive plant found on Oʻahu and Hawaiʻi Island. Documented evidence of its spread in Hawaiʻi helps inform efforts to address invasive species. Photo courtesy of Forest and Kim Starr}

In 2000, Forest and Kim Starr, biologists with the University of Hawaiʻi, accepted an unusual challenge: drive all the roads of Maui at 5-10 miles per hour to look for plants that might be good targets for eradication. On the side of Olinda Road, they spotted a lone tree with large, umbrella-like leaves. It was bingabing, or Macaranga mappa.

If you’ve been to Hilo, you may know the plant; it lines roadsides and low elevation forests. But even after driving all the roads of Maui, the Starrs only found the lone plant upcountry. Why hadn’t it invaded the roadsides here?

Bingabing could have spread, it was just early in the process; the Starrr’s were in search of plants like bingabing, invasive species that were still early in their invasion and hadn’t yet started spreading.

_{An invasion curve illustrates the feasibility of eliminating an invasive species and highlights the importance of finding pests early on. Graphic by University of Florida, IFAS}

An invasion curve shows how a species spreads after its initial introduction and also illustrates the feasibility of eliminating a species. “If there are only a few individuals, it will take time before the population starts to increase dramatically,” explains University of Hawaiʻi professor and researcher Curt Daehler. Daehler studies what factors contribute to a plant’s invasiveness. “There are thousands of introduced species present in Hawaiʻi that aren’t invasive,” he says. “The goal of a plant is to thrive, so what keeps them from spreading? Certain species have a missing pollinator, or the plant is in the wrong location,” explains Daehler.

Stopping an invasive species early— during the lag phase— is an important factor for eradication. But it’s also the most difficult time for detection because their numbers are so low. Having better information about how quickly a species might start to spread can help with prioritizing targets. Estimates of lag time for introduced plants were once presumed to be very long, more than 100 years in some cases. These early estimates were based on indirect evidence and didn’t focus on plants from a tropical environment. To better understand lag times, Daehler says you’d need to intentionally plant a species and watch for its spread. It turns out the Lyon Arboretum in Mānoa Valley on Oʻahu had done exactly that.

*_{Harold Lyon planted hundreds of trees in what is now Lyon Arboretum in an urgent attempt to protect the watershed above Mānoa. Photo courtesy of University of Hawaii.}*

A hundred years ago, the slopes of Mānoa Valley were bare. For decades, feral cattle had grazed the slopes, causing rain to run off the land rather than fill the aquifers; sugar plantation owners were justifiably alarmed. They sought the help of plant pathologist, Harold Lyon. He advocated for protecting the remaining native forests, but also recognized the urgent need to restore vegetation. On a plot of land that eventually became the Lyon Arboretum, he planted hundreds of species from around the world looking for ones that spread swiftly to stabilize the soil and support aquifer recharge. His staff collected detailed information as the plants spread onto nearby land and up low-elevation slopes.

Today, the ability to spread quickly into new areas is a hallmark of an invasive species. Realizing the value of Lyon Arboretum data, Dr. Daehler examined the historic planting records and the documented spread to obtain lag times for 23 plant species known to be invasive in Hawaiʻi. He found that lag times were much shorter than previously estimated. “As soon as they reach maturity, these trees start spreading.” He published his findings to help others address known invaders early.

One of the trees Lyon studied was bingabing. Foresters planted bingabing to support reforestation on Oʻahu; it is now widespread in low-elevation forests. On Hawaiʻi Island, bingabing was seeded by aircraft following a fire in Hilo. It has continued to spread from that initial introduction and today, dense stands crowd the forests surrounding Hilo.

The history of bingabing on Maui appears to be limited to single introductions. Crews from the Maui Invasive Species Committee removed the tree on Olinda Road, and plants from two other sites. Bingabing is one of a dozen species of invasive plants eradicated from Maui before they could spread.

Harold Lyon was concerned about watershed health; had he known the outcome of some of his plantings, he likely would have chosen differently. Today, we have a choice, and a wealth of information about plants’ invasiveness, thanks in part to Dr. Daehler’s work. He helped launch the Hawaiʻi Pacific Weed Risk Assessment (HPWRA), which serves as a background check for plants by predicting the likelihood a species will become invasive in Hawaiʻi. Resource managers, horticulturalists, and farmers can use the HPWRA before choosing to purchase or plant a new species, helping to prevent the introduction of a new invader. The only thing better than eradicating an invasive species early is preventing its introduction in the first place. Learn more and take advantage of the HPWRA at www.plantpono.org.

Lissa Strohecker is the public relations and education specialist for the Maui Invasive Species Committee. She holds a biological sciences degree from Montana State University. Kia’i Moku, “Guarding the Island,” is prepared by the Maui Invasive Species Committee to provide information on protecting the island from invasive plants and animals that can threaten the island’s environment, economy and quality of life.

This article was originally published in the Maui News on February 10, 2024, as part of the Kia‘i Moku Column from the Maui Invasive Species Committee.

Read more Kiaʻi Moku articles

In 2002, an unusually large and strange-looking chameleon turned up in a remote area of West Maui. The resulting media attention led to the detection of a population of the same species in Makawao. These lizards weren’t the familiar Jackson’s chameleons but a new and different species: veiled chameleons. These invaders, illegally introduced to Hawaiʻi posed a threat to our endemic forest birds and snails. Staff from the Maui Invasive Species Committee (MISC), Hawai’i Department of Agriculture and Department of Land and Natural Resources launched nighttime surveys, scouring the vegetation in the backyards of Makawao looking for these cryptic reptiles.

Veiled chameleons pose a risk to native birds in Hawaii. Thanks to community reports, these tree-dwelling arboreal predators were detected early and have efforts to eradicate them have proven effective. “Veileds” can be recognized by the shark-fin shaped casque on their head. MISC file photo.

During initial searches, the teams found chameleons quickly: they were distinctive, larger than their horned cousins and sporting a “shark fin” head, and clung to tree branches as they slept. The community helped by allowing searchers into their backyards and finding and turning in chameleons themselves.

In 2003, search crews and residents captured a total of 102 lizards, but over time, the numbers steadily declined. From multiple chameleons per night, searchers started to find only one or two per week. Then came months when crews came back from a week of searching without seeing a single chameleon. Searchers counted Jackson’s chameleons to stay focused on their task. As numbers continued to drop, the time between searches increased. The last capture was in 2008. In 2012, after a final search and outreach to the community, the agencies agreed: veiled chameleons had been eradicated from all known locations on Maui. Addressing the threat early, with community cooperation, prevented this species’ spread into new areas, including higher-elevation rainforests, the last habitat for our native birds and snails.

Both the language and processes used to stop an invasive species before it becomes widespread mirror the terms used to address a contagious and serious disease outbreak. As the COVID-19 pandemic spread worldwide and governments implemented social distancing measures, Jane Mangold, an invasive plant specialist at Montana State University, considered the similarities:

“One of the most obvious parallels is the importance of prevention, early detection, and rapid response. ‘Flattening the curve’ has been stated repeatedly by experts keeping us informed about the pandemic; the rationale behind this phrase is that by slowing the spread of the disease, medical providers will have more time and resources to treat those in need, and ultimately save more lives,” Mangold said.

Initially, reducing the spread of the chameleons was costly: routinely searching every few weeks to find chameleons faster than they could spread. So too for COVID-19, after months of social distancing and substantial economic impacts, the number of new cases has dropped and the curve has flattened. There are other parallels between controlling the spread of human disease and pests.

Addressing biological invasions early prevents later impacts.

Those last few chameleons were likely the most time-consuming and expensive to remove, but if crews hadn’t captured them, the population could have rebounded. Working past the frustration and searcher fatigue to find the few remaining individuals was critical to achieving eradication. While eliminating a small population of lizards is not readily comparable to addressing and suppressing a global health pandemic, similar elements lead to success: widespread cooperation, diligence, and commitment to seeing the effort through the long tail of the curve a resolution. And, of course, for both the chameleon and COVID-19, local reintroduction remains a possibility.

We can all do our part to maintain vigilance. And if you happen to see a strange chameleon with a shark-fin on its head while you are at home, report it to MISC at 573-6472 or through 643PEST.org. Anyone can turn in veiled chameleons and other illegally owned reptiles through the state Department of Agriculture’s amnesty program.

Learn more about the veiled chameleon at dlnr.hawaii.gov/hisc/info/invasive-species-profiles/veiled-chameleon/.

This article was originally published in the Maui News on June 13, 2020 as part of the Kia‘i Moku Column from the Maui Invasive Species Committee.

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