Biology Reference
In-Depth Information
Prediction success can be hindered by the phenomenon of “invasional melt-
down,” a term coined by Simberloff and Von Holle (1999). Invasional meltdown is
“the process by which a group of NIS facilitate one another's invasion in various
ways, increasing the likelihood of survival and/or of ecological impact, and possi-
bly the magnitude of impact.” This phenomenon is especially relevant to the orna-
mental horticulture industry, which introduces hundreds of NIS as well as pest and
pathogen “hitchhikers” on these ornamental plants into our landscapes that may
synergistically interact in the future. Once a NIS is introduced, the unforeseen suite
of future complex interactions greatly increases the difficulty of predicting the con-
sequences of invasion (Mooney 2005).
NatureServe, in cooperation with The Nature Conservancy and the US National
Park Service, developed a systematic assessment protocol that uses a set of ques-
tions and scientific documentation to rank invasive nonnative plant species (Morse
et al. 2004). The Invasive Species Assessment Protocol is a tool for assessing, cate-
gorizing, and listing nonindigenous plant species on the basis of their impact on
biological diversity. Each species has an overall ranking, which is composed of
subrankings from four areas: (1) ecological impact, (2) current distribution and
abundance, (3) trend in distribution and abundance, and (4) management difficulty.
To date, 452 nonnative plant species occurring outside cultivation in the USA are
ranked; the goal of the program is to rank 3,500 of these nonindigenous plant spe-
cies. This objective ranking system and the documented list of invasive nonnative
plant species serve as an effective decision support system for the ornamental hor-
ticulture industry to adopt for deciding which nonindigenous plant species to stop
selling. The Invasive Species Assessment Protocol determines the ranking on a
national distribution, and therefore the rank must be interpreted in the context of a
specific region since a plant may not be problematic in all or most areas. However,
in many cases a text description of the invasive nature of each species mentions the
regional nature of invasiveness. In an attempt to consistently describe and catego-
rize invasive nonnative plant species, some states, e.g., Florida (Fox et al. 2005),
and Virginia (Heffernan et al. 2001), have also developed relatively rigorous assess-
ment systems. Additionally, the Exotic Pest Plant Councils (EPPCs) rank nonnative
plant species by their impact within specific regions or states [e.g., SE-EPPC
(http://www.se-eppc.org/), FLEPPC (http://www.fleppc.org/list/list.htm), Cal-IPC
(http://www.cal-ipc.org/)].
The call for improved and widespread prediction tools has been mandated by the
US government. In an attempt to gain control of the importation of potentially NIS,
the Animal and Plant Health Inspection service (APHIS, a branch of the USDA), the
entity responsible for preventing the introduction of plant and animal pests,
commissioned the National Research Council's Board on Agriculture and Natural
Resources (BANR) to comprehensively review scientific knowledge regarding inva-
sive NIS. BANR was charged to develop “risk assessments, identify potential invad-
ers, and guide the strategic allocation of its resources to safeguarding plant life in the
United States.” In response to this charge, BANR established the Committee on the
Scientific Basis for Predicting the Invasive Potential of Nonindigenous Plants and
Pests in the USA, which was composed of experts in disciplines related to the invasive
