Final Comprehensive Conservation Plan - U.S. Fish and Wildlife ...

Hakalau Forest National Wildlife Refuge
Comprehensive Conservation Plan
2006-2007, the Service controlled approximately 2,400 ac of gorse. Ongoing monitoring and
treatment for seedlings and regrowth occurs in all treated areas. Gorse is not shade tolerant;
reforestation efforts are expected to increase the dense canopy of native forest and prevent gorse
from reestablishing. A partnership between the Refuge and DHHL has resulted in an attempt to
contain the spread of gorse by planting native koa trees and thereby shading out the species in a
195-acre area immediately above and adjacent to the HFU.
The State Department of Agriculture has, over the past 20 years, released a host of biocontrol insects
to control gorse. On Maui, an introduced caterpillar (that eats the flowers) reduced the reproductive
potential of the species by 73 percent. In 1989, the moth Agonopterix ulicitella was introduced to
control gorse by feeding on new shoots (Loope et al. 1992). The thrip Sericothrips staphylinus
browses on gorse plants, but it is not yet clear how much this species will contribute to control in
Hawai„i (Hill et al. 2001). The gorse seed weevil Exapion ulicis, which feeds on gorse foliage and
flowers for most of the year, has also been introduced to Hawai„i (Davies et al. 2008).
Japanese Mat Rush (Juncus effuses)
Japanese mat rush is known to occur in shallow marshes and disturbed, moist areas around the globe.
It is able to establish monospecific stands in former agricultural areas and in disturbed forest areas
due to vigorous clonal growth and high seed production (Smolders et al. 2008). The light seeds allow
for easy dispersal and the dense tussocks and culms of the rush expand underground by lateral
rhizomes. In nutrient-poor areas, mowing has proven to be an effective removal technique (Smolders
et al. 2008).
This species is common on the HFU. This perennial herb is naturalized along streams, ponds, and
bogs in Hawai„i. It is known to occur between 3,280-6,562 ft (Wagner et al. 1999). From 1987-2007,
the frequency of this species on the HFU rose by 13.7 percent (Jacobi and Price 2007). Japanese mat
rush has also invaded native Carex bogs. Pigs eat the native sedge, removing the native plants and
facilitating the increase and spread of Japanese mat rush (Jeffrey, pers. comm.).
Kikuyu Grass (Pennisetum clandestinum)
Kikuyu grass is a fast growing grass species that forms mats and spreads by rhizomes and stolons.
Kikuyu grass is native to eastern Africa, but has spread throughout the tropics and subtropics (Holm
et al. 1977). It occurs primarily in cool fertile areas (Scowcroft and Jeffrey 1999) between sea level-
6,600 ft (2,000 m) elevation. It propagates vegetatively because the small, inflorescences rarely
produce seeds (Holm et al. 1977). It is shade-tolerant, and the root morphology may also be altered in
shaded areas (USFWS 1996b).
Kikuyu grass is a particular management concern because the species forms dense mats, preventing
the establishment of native seedlings. It competes with native seedlings for nutrients, light, and water
(Scowcroft 1992), and increases the frequency and intensity of fire (Smith and Tunison 1992).
Kikuyu grass, in combination with gorse, was determined to be the primary fuel for wildland fires at
the HFU in 2000. In addition, the plant can withstand defoliation by natural processes, such as frost,
drought, hurricanes and treefalls, as well as grazing (Holm et al. 1977, USFWS 1996b). Furthermore,
Kikuyu grass has been reported to possess allelopathic substances (Smith 1985). For these reasons, it
is a federally listed noxious weed and according to the USFS and DOFAW it is considered a highrisk
weed species for creating ecological and economic harm in Hawai„i.
Chapter 4. Refuge Biology and Habitats 4-105