Biology Reference
In-Depth Information
the desire to focus management efforts, whether for control or early detection, on a
reduced subset of the total species pool where they will be most effective.
2.4.2.1 Prioritization for Control of Nonnative Plants
Prioritization for control efforts has commonly been used to maximize the cost-
effectiveness of efforts designed to manage species that are known to reside within
a particular management unit. When faced with lists of tens to hundreds of invasive
species, land managers need guidance on how best to allocate scarce resources to
control them. Randall et al. (2008) recently reviewed 17 examples of systems used
to help place nonnative plants into categories to facilitate their management, and
compared them to a system that they developed themselves (Morse et al. 2004).
Twelve of these systems were designed to prioritize management actions for non-
native species that are already established within a management unit. Two priori-
tized among invaded sites (Timmins and Owens 2001; Wainger and King 2001) and
ten prioritized among invaded species within sites, states, or nations (Orr et al.
1993; Weiss and McLaren 1999; Thorp and Lynch 2000; Champion and Clayton
2001; Fox et al. 2001; Heffernan et al. 2001; Virtue et al. 2001; Hiebert and
Stubbendieck 1993; Warner et al. 2003; Morse et al. 2004). Only two (Warner et al.
2003; Morse et al. 2004) focus heavily on species' impacts on biodiversity, whereas
the rest focus mostly on feasibility of control, or potential effects on agricultural,
horticultural, or other economic factors.
Prioritization decisions are typically made based on some combination of the
following four factors:
1. The relative ecological and/or economic threats that the species pose
2. Their potential to spread and establish populations quickly (i.e., their “weediness”)
3. Their potential geographic and/or ecological ranges
4. The feasibility in which they can be controlled (Timmins and Williams 1987;
Hiebert and Stubbendieck 1993, Hiebert 1998, Weiss and McLaren 1999; Fox
et al. 2000; Mehrhoff 2000; Warner et al. 2003; Morse et al. 2004)
The scoring systems for these prioritization efforts generally emphasize the threat
potential and spread potential over the other two factors, with the weighted sum of
the ranks for all four resulting in the net priority assessment.
Although the large number of systems may appear bewildering at first, many can
be directly applied to a wide variety of areas and situations. Using an existing sys-
tem will reduce the cost of developing a new system and provide managers with
choices and flexibility. However, it is important to stress the necessity of selecting
the system that is most appropriate for a given situation (Randall et al. 2008).
Prioritization is generally done for species that are known to be invasive, or for sites
that have high conservation value but may be susceptible to invasion. In some instances,
both species and sites can be prioritized for management actions (Timmins and Owens
2001), and if adequate resources and information are available this can be an extremely
useful strategy. Prioritization is most often based on a synthesis of preexisting studies,
