Pigs in Manoa: While our cover article this month focuses on pigs at Hakalau, on the Big Island, another study just published in Pacific Science looks at pigs in the forests of Manoa Valley, on O`ahu. The study, by a team of researchers at the University of Hawai`i’s Department of Natural Resource and Environmental Management, compared runoff from plots where pigs had been excluded to that from plots where pigs were still present.
The article, “Runoff, Sediment Transport, and Effects of Feral Pig Exclusion in a Forested Hawaiian Watershed,” found that the concentration of total suspended solids in runoff from both types of plots was similar. However, authors Dashiell Dunkell, Gregory Bruland, Carl Evensen, and Creighton Litton found that the volume of runoff from the plots without pigs was significantly less than that from the plots where pigs were not excluded.
What surprised the authors was the sheer volume of runoff from the small plots. In wet-season rainfall events (in December and March), “runoff regularly exceeded collection bucket capacity… Despite the fact that runoff plots drained an area of only 5.04 m2, the amounts of runoff were extremely large, ranging from 7.5 to >128 liters in December.” That level, they note, was higher than any record reported in previously published literature.
Because the plots had been set up for just a year before the study began, they write, “it may simply have been too early for differences [in TSS] to be detected.” But they did discover “large Psidium cattleianum [strawberry guava] recruitment” to be higher in the unfenced plots. “There were twice as many P. cattleianum saplings and seedlings in the unfenced versus the fenced plots, indicating that pigs may be promoting further plant invasions.”
Cattle on Kaua`i: Like pigs, cattle can also wreak havoc on an ecosystem. A new study published in the Journal of Environmental Management has found that the presence of cattle near Waipa stream in North Kaua`i and reduced riparian canopy cover there were associated with higher concentrations of the potentially harmful Enterococcus bacteria.
The research was a collaboration of authors from the non-profit Surfing Medicine International, the University of Hawai`i, the University of Nevada at Reno, and the University of California at Davis. They include Guy Ragosta, Carl Evensen, E.R. Atwill, Mark Walker, Tamara Ticktin , Adam Asquith and Kenneth Tate.
The article, “Risk factors for elevated Enterococcus concentrations in a rural tropical island watershed,” which is available online at Science Direct, states that cattle presence near water quality monitoring sites was associated with an increase of 99.3 MPN (most probable number)/100 ml of Enterococcus in individual samples. Also, each one percent decrease in riparian canopy cover was associated with a 3.6 MPN/100 ml increase of waterborne Enterococcus.
The authors also found that summer samples had substantially higher concentrations of Enterococcus than winter ones.
Summer Conference: Although it’s too late to get the cheap rate, ample time remains to register for this year’s Hawai`i Conservation Conference, which will be held August 2-4 at the Hawai`i Convention Center in Waikiki.
Keynote speakers on this year’s theme, “Island Ecosystems: The Year of the Forest,” will be poet laureate and former Environment Hawai`i board member William Stanley Merwin, as well as Willaim Kostka, executive director of the Micronesian Conservation Trust.
Cost for the entire conference, including lunch coupons, is $370 or $170 for students and interns. One-day rates are also available. Visit http://hawaiiconservation.org/activities/hawaii_conservation_conference for more information.
Volume 21, Number 12 — June 2011