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

Hakalau Forest National Wildlife Refuge
Comprehensive Conservation Plan
disturbed areas throughout the Hawaiian Islands. It can form dense thickets on steep slopes (Wagner
et al. 1999).
Christmas berry is considered a pioneer species because it quickly colonizes disturbed areas. The
invasive attributes of Christmas berry include a large number of fruits, bird dispersal, and a tolerance
to shade, fire, and drought. Furthermore, Christmas berry is believed to have allelopathic properties,
which increases its competitive ability with neighboring plants (Hight et al. 2003). Due to these
characteristics, this species is recognized as a noxious weed by the Hawai„i Department of
Agriculture.
Three biocontrol insects have been released in the Hawaiian Islands to control this species. This
includes a seed-feeding beetle in 1960, a leaf-rolling moth in 1954-1956, and a stem-galling moth in
1961-1962 (Hight et al. 2003). An accidentally introduced seed-feeding wasp has also been found
attacking seeds of Christmas berry. A foliage feeding sawfly was tested as a potential biological
control agent for Christmas berry; however, this species was not introduced due to its risk to the
native „ohe kukuluae„o (Hight et al. 2003).
English Holly (Ilex aquafolia)
English holly grows as a tree or shrub reaching over 16 ft in height. Growing in mesic to wet forests
and open bogs, English holly shades out native groundcover species (Jacobi and Price 2007).
Although this species is relatively slow growing, it is easily dispersed by birds due to the presence of
red fleshy fruits (USFWS 1996b).
English holly was planted at the HFU by the previous landowners. Control activities began at the
HFU when the holly infestation was estimated at 500 ac. Between 2006-2007, 102 ac were treated.
This species can be controlled using EZJect®, which injects glyphosate-filled capsules into the tree
cambium layer (Van Driesche and Van Driesche 2000, NRCS 2005). Treatment of germinating seeds
must be continued to maintain control. Even if English holly is eliminated from HFU, birds will
continue to bring seeds into the forest from nearby infected areas.
Florida Blackberry (Rubus argutus)
The Service considers Florida blackberry to be a primary invasive plant species of concern. Native to
the central and eastern United States, Florida blackberry has been naturalized in the mesic and wet
forests and subalpine grasslands in Hawai„i. It primarily occurs from 656-7,546 ft (Wagner et al.
1999). This shade-intolerant species grows into dense thickets in forested and disturbed areas lacking
extensive understory. The stems of Florida blackberry are covered with straight or hooked thorns,
and the fruit is bird-dispersed (USFWS 1996b). Once established, it spreads by underground
rhizomes (Loope et al. 1992).
Blackberry is mainly treated at the HFU June-October using 0.5 percent Garlon 3A®, a foliar-applied
spray that does not kill native plants (Jeffrey, pers. comm.). Estimates by the Natural Resources
Conservation Service (2005) suggest that this species infests approximately 10,300 ac of open and
closed canopy forest. In 2006, 774 ac were treated and an additional 350 ac were treated in 2007.
Although intense control efforts have been in place for this species, a slight increase in the blackberry
population (8.6 percent) occurred between 1987-2007 (Jacobi and Price 2007). This increase may be
Chapter 4. Refuge Biology and Habitats 4-103