Catching Invasive Plants Early: The Pacific Island Parks' 2014 Pilot Surveys

Aggressive non-native plants — invasive species — are among the biggest threats to the spectacular endemic plant communities of Pacific island national parks. Hawai‘i Volcanoes National Park (HAVO), Haleakalā National Park (HALE) and many other parks have long fought them, but the battles are costly and slow, and some invasions pass the point of no return.

Invasive kahili ginger (Hedychium gardnerianum) at Hawai‘i Volcanoes National Park. Image from the Park Service's page.

Why early detection

The Pacific Island Inventory & Monitoring Network (PACN I&M) already maps native and non-native plants and monitors long-term plots in HAVO, HALE and other parks. But those data don't include targeted searches of invasion corridors — roads, trails, fence lines — where new non-native plants are most likely to take hold. Finding and removing a potential invader before it spreads is the cheapest way, and sometimes the only chance, to eradicate it, so the network is developing an early detection monitoring protocol.

In summer and fall 2014 it ran three pilot studies, to:

1. give the parks immediate data on new species;
2. test the methods for systematically searching for, finding and reporting new non-native plants;
3. estimate the time and cost on a small scale before going network-wide.

Kahuku Unit, Hawai‘i Volcanoes

The largest pilot was in HAVO's Kahuku Unit, acquired in 2003 and less studied than the rest of the park. Its farming history and range of climates and habitats make it a prime target for invaders. With almost 130 miles of roads and trails — far too many for a two-person crew — the busiest routes came first.

• The crew walked the routes; for any unknown plant they took a GPS point and photos, and a sample if needed.
• Identified plants were checked against lists for Kahuku, the rest of HAVO, and Hawai‘i Island, to tell a plant the surveyors simply didn't know from a new arrival.
• In about a month they covered over 76 miles, up to 6 miles a day, and nearly all the high-traffic areas.

Result: 30 unreported species in parts of Kahuku — 11 new to Kahuku, 3 new to HAVO, and 1 new to the Big Island, the grass Dicanthium annulatum, which joins the park's species database with the three new to the park. Most were grasses and herbs that make lots of small, easily spread seeds, and the busiest roads and trails had the most new species.

Kīlauea summit, Hawai‘i Volcanoes

HAVO asked for a study at the summit, where visitor impacts are greatest. Botanists surveyed about 19 miles of busy trails, paths and parking lots from Jaggar Museum to Kīlauea Iki. The residential area by Volcano House was the most interesting: several planted ornamentals, including a Syzygium species — a member of the highly invasive family Myrtaceae — which the park now plans to eradicate.

Haleakalā summit district

Complementing park-funded road surveys, I&M biologists Elizabeth Urbanski and Michelle Osgood surveyed about 40 miles of trails over 12 days between September and November 2014. They found 3 plant species in 4 locations that met the early detection criteria: strawberry guava, one of the park's worst invaders, in a new place along the Kaupō trail, and Wahlenbergia gracilis, never before recorded in the park, off trail in the front country.

What next

HAVO staff are reviewing the new species to judge which could become invasive; any high-risk species will be targeted for eradication. Meanwhile the network is evaluating the pilots to improve its Early Detection of Invasive Plants protocol, and whether early detection can work at a larger scale across HAVO and the other Pacific island parks.

More: the Pacific Island Inventory & Monitoring Network, and a PDF of this report.

Sources

Based on "Early Detection Pilot Studies," National Park Service, by M. Wasser and A. Ainsworth (NPS botanists), with notes by M. Simon and E. Urbanski (NPS), 2015; a work of the United States government in the public domain. Park and program names the import dropped were restored from the live page. The source's two plant photographs, credited to a named photographer, are not reproduced; its "Jagger museum" is spelled Jaggar.