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

Hakalau Forest National Wildlife Refuge
Comprehensive Conservation Plan
Invasive plants can physically displace native species, and/or supersede them by competition for
water, nutrients, or other limited resources. Nonnative plants can also be vectors and hosts for
introduced pests and diseases to which the native species lack natural defenses (Jui et al. 2007).
Some invasive plants have allelopathic properties. Furthermore, compared to native plants,
introduced plants lack their natural enemies in the introduced range, which again gives them a
competitive edge over native species. Some invasive plants are faster growing and can therefore
easily and quickly colonize, establish, and displace native species (Blossey and Notzold 1995).
Island ecosystems are particularly vulnerable to biological invasions (Loope and Muller-Dombois
1989, Denslow 2003). In spite of a multitude of plant species that have been introduced to Hawai„i,
only about 1 percent (130 of 13,000 species) of them are considered invasive and have a negative
impact on the native habitats; however, the Hawai„i DLNR anticipates that an additional 200 -
300 species already present in the State may become problems in the future
(http://www.state.hi.us/dlnr/dofaw/hortweeds/). In general, detrimental invasive plant species exhibit
a lag phase in which the species will exist at low concentrations for a period of time before spreading
across the landscape (Hobbs and Humphries 1995).
Invasive plants are successful in island ecosystems due to a multitude of traits. According to Staples
et al. (2000), invasive plants in Hawai„i share the following biological and reproductive
characteristics:
Adaptable to and capable of thriving in different habitats;
Tolerant of variable conditions (such as light, temperature, moisture);
Fast growing;
Tolerant of disturbance;
Easily dispersible to new localities by seeds, fruits, spores, or vegetative parts;
Produce small seeds/spores early in life;
Long reproductive periods;
Dispersed by animals; and
Need no special germination requirements.
As a result of these traits, control and eradication of introduced weeds has been a top priority of
natural resource managers in Hawai„i (Jacobi and Price 2007). For this reason, several databases
have been developed to assist in invasive plant species control. The Hawai„i-Pacific Weed Risk
Assessment (HPWRA) is a research project conducted by the University of Hawai„i and the USDA
Forest Service to identify plants that pose a high risk in Hawai„i and other Pacific Islands. This
database provides detailed species information and scores species based on the risk of invasion.
HPWRA score for species on the Hakalau Forest NWR are provided in Table 4-10.
Chapter 4. Refuge Biology and Habitats 4-97