Hawaiian Ecosystems at Risk project (HEAR) "New" information on pampas grass*
by Lloyd Loope


pampas grass (Cortaderia selloana)In the mid-1980s, driving the 17 miles daily from my home in Makawao to the research office at Haleakala National Park, an alarming phenomenon about halfway on the journey gradually dawned on me. Starting about the first week in August every year, there would be mass blooming of an ever-increasing patch of South American pampas grass on property behind Sunrise Market (elevation 3300[?] ft) on Crater Road. Colleagues Art Medeiros and Betsy Gagné began noting (in 1987-88) pampas grass seedlings along Crater Road at 4000-6000 ft elevation; several of those roadside plants flowered in 1989. We were at first puzzled because the conventional botanical wisdom was that Hawaii had only female plants of pampas grass, Cortaderia selloana, and that this attractive and benign species never sets viable seed. Art sent some specimens off to the U.S. National Herbarium in Washington, D.C, and we received confirmation that the invasive grass was indeed as we had suspected Cortaderia jubata, an asexual species (that produces abundant viable seeds without sex) known in the botanical literature to be an aggressive invader in coastal California. Then in October 1989, Ted Rodrigues spotted from a helicopter a 10 ft tall seeding pampas grass plant on the Haleakala Crater wall just inside the park boundary in Koolau Gap; it was of course removed promptly, and the site monitored for years for seedlings. There seemed to be every reason to believe that C. jubata if unopposed could widely establish and eventually come to dominate vegetation on Crater walls and elsewhere in Haleakala National Park, displacing native biodiversity. By the mid-1990s, patches of wind-dispersed pampas grass began to be noticed from the air in moist open areas within rainforest high on both East and West Maui.

The two species, C. selloana and C. jubata are extremely similar, but there are many precise botanical mini-characters to distinguish them consistently. We found that plantings of C. jubata were much less common than those of C. selloana, so we began an exploratory campaign to determine whether eradication was a possibility. We were successful at getting C. jubata on the Hawaii Noxious Weed List in 1992, based on our documentation of its damaging characteristics and its well-known behavior in California. With landowner permission, Chuck Chimera led a highly motivated and effective volunteer group in 1992 that dramatically knocked back the burgeoning C. jubata population behind Sunrise Market. Our approach to landowners was that there were two pampas grass species--one invasive and one innocuous. For over a decade this approach was rational, based on the conventional wisdom and scientific literature on the California situation. When the MISC was formed and chose its targets in 1998, pampas grass was deemed a necessary target, second only to Miconia in its habitat modifying ability, but there was a lot of discussion about the non-feasibility of targeting just one of the two species because of their striking similarity.

Conventional and scientific wisdom about the innocuous nature of C. selloana had changed by 2000, as a result of research by John Lambrinos, who completed his Ph.D. thesis at UCLA on alien Cortaderia in California. Lambrinos, now a Landscape Ecologist in the Horticulture Department at Oregon State University, came to Maui that year, briefed me on his findings, and gave me a pre-publication copy of his article that was published in 2001 in the Journal of Ecology, "The expansion history of a sexual and asexual species of Cortaderia in California, USA." Lambrinos found from herbarium specimens that both species were introduced to California in the mid-1800s, that the invasiveness of sexual C. selloana has increased over time (apparently through evolution in California over the past century plus), and that C. selloana is now more invasive and damaging to California ecosystems than C. jubata. Literature from New Zealand, Australia, and South Africa is consistent regarding the aggressive invasiveness of C. selloana.

MISC is now spending ca. $200,000 per year just trying to contain the damage by C. jubata, with no hope of eradication. There is an excellent opportunity to eradicate C. selloana before it becomes aggressively invasive, but that will require strong public support.

Note: If anyone desires more detailed information, I recommend reading the Lambrinos 2001 paper. If you're interested, e-mail me at Lloyd_Loope@usgs.gov.
*as submitted to the Maui Invasive Species Committee (MISC) on 05 August 2006 for its public newsletter
The Hawaiian Ecosystems at Risk (HEAR) project is currently funded by the Pacific Basin Information Node (PBIN) of the National Biological Information Infrastructure (NBII) through PIERC (USGS) with support from HCSU (UH-Hilo). More details are available online. Pacific Basin Information Node (PBIN) National Biological Information Infrastructure (NBII)
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