Each year, the Hawai’i Conservation Alliance (formerly known as the Secretariat for Conservation Biology) brings together hundreds of researchers, land managers, agency officials, students, and others with an interest or stake in the preservation of Hawai’i’s natural resources. This year’s conference was held in Honolulu in early July.
This month and next, Environment Hawai’i presents summaries of just a few of the presentations.
Early Warnings On Invasives
What’s being done to prevent more species from gaining access to Hawai’i’s potentially welcoming ecosystems? Forest and Kim Starr of the Haleakala Field Station, U.S. Geological Survey, Biological Resources Division, discussed strategies to identify and reduce newly invasive plant threats in Maui. In so doing, they showed the incredible amount of work and dedication needed to recognize and combat new plant species before they get out of control.
The Starrs compared a list of weeds known to be invasive elsewhere with a list of plants known to be cultivated on Maui. The result was a list of more than 100 potentially invasive plants already being grown on the island. A ground survey and expert interviews disclosed more than 16,000 locations where the listed species are found.
The researchers detailed three weeds of particular interest: the Port Jackson fig (Ficus cf. platypoda), silver cotoneaster (Cotoneaster pannosus), and Jerusalem thorn (Parkinsonia aculeata). The fig destroys native canopy trees such as koa and ‘ohi’a by germinating on them and eventually smothering them. It promotes other plant invasions by providing resources normally absent in Hawaiian forests. In addition, it provides an abundant food source for introduced birds, which disperse its seeds over long distances. According to Kim Starr, “at this time islandwide control does not seem likely.”
A more likely candidate for control is the cotoneaster, identified as a weed in California and Australia. This popular ornamental produces bright red fruits, which are consumed by birds and pigs. The plant can form thickets, germinate in either dense shade or full sun, and is able to survive at high elevations. Most cotoneaster planted as ornamentals are found in mid-elevation residential areas in east Maui. However, the Starrs found a few outlier populations, including one in Haleakala National Park (since controlled). The most promising candidate for complete eradication is Jerusalem thorn, a weed in the West Indies, Australia, and Micronesia. Horticulturalists like it because of its showy flowers and ability to tolerate drought. The surveyors found only two populations on Maui, one of which has already been removed.
“The more you look, the more you find,” Forest Starr said. “Early detection is possible if sufficient time and resources are dedicated.” The Starrs’ group detected many species that had not yet been recorded on Maui but which “were actually well beyond the point of realistic eradication.” They suggested that members in the audience start looking for weeds locally and take unknown and new plants to local experts for cataloging. With screening and active monitoring, it may be possible to identify the next miconia, or strawberry guava, or banana poka, and nip it in the bud.
– Trevor Stokes
Tracking Conservation
How can scientists and land managers determine if conservation efforts are working? Karen Poiani addressed this topic with a discussion of the attempt by The Nature Conservancy to establish guidelines to do precisely this.
TNC has developed a list of seven measurements, or metrics, to assess the general health of terrestrial landscapes. The list, still provisional, includes ungulate activity, weed presence, size of the native ecosystem, extent of adjacent ecosystems, percent native canopy cover, percent native understory, and presence of sensitive indicator plants. The metrics are assessed through remote imaging or ground-based surveys.
“Some of [the criteria] are direct measures of the threats in our native ecosystems and some of them are more direct measures of the ecosystems themselves,” Poiani said. While the criteria are not species-centric, she added, TNC does plan to develop a set of indicator plant species that will help assess vegetation composition in a particular region.
Another important measurement is the health of surrounding landscapes. If these surrounding areas are themselves dominated by non-native plants, she said, “then we are not being successful in our conservation efforts.”
Almost half of the metrics require transects. Determining how many to conduct, and where, Poiani said, are questions without easy answers.
The criteria are currently being tested on TNC-owned land in east Moloka’i and are partly based on existing land transects.
“We strove in our template for simplicity and ‘do-ability’ across large spatial scales. Our managers think it’s too much, our scientists don’t think it’s enough. Have we compromised so much that we are collecting relatively meaningless data where expert opinion would have been good enough anyway? We’re not sure,” Poiani said.
“The resources that we would have to gather and spend even collecting and monitoring this much information is significant. Before we go out and start collecting this information in the field, we really want to make sure it’s the right way to start.”
– T.S.
‘Aki Trees
Fourteen years ago, Jaan Lepson, then a graduate student at the University of Hawai’i, noticed tiny pockmarks, about a quarter of an inch in diameter, on an ‘ohi’a tree at Hakalau Forest National Wildlife Refuge, on the island of Hawai’i. Later, he determined that the holes were made by the bright yellow ‘akiapola’au (Hemignathus munroi), an endangered Hawaiian forest bird. The ‘aki were already known to feed on insect larvae dug out of trees with a dual-purpose bill; Lepson discovered that they fed on sap as well.
Recently, Liba Pejchar of the University of California at Santa Cruz followed up on Lepson’s discovery. She investigated the reason the ‘aki feed on sap, how they select trees to tap, and differences between ‘ohi’a selected for sap and other ‘ohi’a.
In her study of 100 ‘ohi’a sap trees (” ‘aki trees,” as she calls them) at Hakalau, Pejchar found that the sap flow in the trees selected by the ‘aki was ten times greater than that in control ‘ohi’a. The ‘aki trees were generally found to be on east-facing, convex slopes, suggesting that the more light and moisture the trees have, the better the quality of their sap. Pejchar also found the ‘aki trees to be thicker and taller, with smoother, thinner bark.
Like the ‘aki themselves, sap trees are rare, with just one or two found in a given hectare of forest. Still, Pejchar says, the trees are valuable. Their sap is a “rare and potent energy source,” and may be a food supplement for the ‘aki in times of low insect or nectar availability.
— Teresa Dawson
Volume 14, Number 3 September 2003
Leave a Reply