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

Hakalau Forest National Wildlife Refuge
Comprehensive Conservation Plan
due to the removal of browsers (Van Driesche and Van Driesche 2000). Continued control efforts
and monitoring are ongoing at the HFU.
German Ivy (Senecio mikanioides)
This fleshy perennial vine occurs in dry forests, moist forests, and coastal areas in the Hawaiian
Islands. In particular, it climbs tall trees in the forest on Mauna Kea, Mauna Loa, and Hualālai
(Motooka et al. 2003). German ivy prefers high light areas, where it can smother native vegetation
(Wagner et al. 1999).
Various herbicides, such as triclopyr and foliar glyphosate, can be used to control German ivy.
Effectiveness may be enhanced by cutting and drying the stems, while spraying the remaining parts
with glyphosate (Motooka et al. 2003). No control work has been conducted for this species at either
the HFU or KFU.
Gorse (Ulex europaeus)
Native to Western Europe and coastal areas of the Mediterranean, gorse was first recorded in Hawai„i
in 1920. It has also spread to several other regions such as New Zealand, Australia, Chile, and
California. This woody legume is spiny and can grow up to 10 ft in height (Davies et al. 2008). It is
highly adapted to disturbed landscapes with low fertility and nutrient depleted soils, such as
pastureland. It prefers more acidic soils, with a pH 4.5-5.0, and can acidify surrounding soils (Leary
et al. 2006). In Hawai„i, flowering can occur for a 9-month period (Tarayre et al. 2007).
Subsequently, a large number of seeds are produced in small pods (Davies et al. 2008).
Dense, impenetrable thickets of even-aged, mature plants grow on Maui and Hawai„i Island (Leary et
al. 2006). However, unlike other invasives present on the Refuge, gorse infests high-elevation pasture
areas rather than forest. The original gorse infestation on the HFU was estimated at 3,200 ac but was
reduced to 75 ac by 1999. The infestation is largely concentrated in the southern portion of the
Refuge near Pua „Ākala Ranch (Tomonari-Tuggle 1996). The current frequency of gorse on the
Refuge is approximately 0.1 percent (Jacobi and Price 2007). Although the infestation of gorse on the
HFU is minor, the adjacent Department of Hawaiian Home Lands (DHHL) ranch lands are heavily
infested. The gorse infestation in this area increased from 4,942 ac in 1992 to over 9,884 ac in 2006
(Leary et al. 2006).
Thick gorse growth completely inhibits regeneration of native species. Perennial growth of this
species can occur up to 30 years. Other characteristics that contribute to the invasive ability of gorse
are its nitrogen fixing ability and large persistent soil seed bank. The seeds can remain in the seed
bank for 30-60 years (Jeffrey, pers. comm.). Similar to the nonnative grass species, gorse serves as a
fuel for fires by posing a risk of ignition and sustaining the spread of fires; a 12 in patch can produce
60 ft flame length (USFWS 2002a). As a result of these characteristics, it has been designated as a
noxious weed species in the State of Hawai„i (Leary et al. 2006).
Spraying with an herbicide and then burning once the gorse is dead was originally used to control
this invasive; however, the gorse sprouted vigorously from the trunk and seedlings were found to be
stimulated using this technique. Currently, the Refuge controls gorse year-round (primarily
September-May) by using a bulldozer with a rake to pull out large rooted plants and then spraying
small plants with Garlon 3A at 3 percent foliar spray with Silwet (Jeffrey, pers. comm.). During
4-104 Chapter 4. Refuge Biology and Habitats