Biology Reference
In-Depth Information
can be used to design programs focused on detecting the initial establishment of
species that currently occur elsewhere in the region.
Lists that are compiled to specifically document the status of nonnative plants
are highly preferable over lists that are compiled for other purposes, such as general
botanical surveys or validation of vegetation maps. Monitoring plans vary accord-
ing to their intended purpose, and there is no single optimal plan for all applica-
tions. Consequently, the resulting species lists vary in level of specificity, accuracy,
and scope. For example, surveys done to validate vegetation maps are often focused
on plant associations, noting only dominant species and other species of interest.
Rare occurrences (i.e., the primary targets for early detection) may be left off inten-
tionally or simply overlooked. Accordingly, surveys that are not designed to spe-
cifically inventory nonnative plants will most likely underreport the actual number
of nonnative species present in the monitoring area.
Numerous types of useful ancillary information can be included in species lists and
are almost always useful in designing early detection programs. Estimates of distribu-
tion and abundance in the area of concern, even if they are qualitative (e.g., widely
distributed but not abundant), are the most basic types of ancillary information that can
be included. If the program goal is to monitor areas based on statistical models of the
likelihood of a species colonizing a site, then geo-referenced data on environmental
conditions where the species is known to occur are highly desirable (see later).
Although it may seem counter-intuitive, it is often useful to also have data on
environmental conditions where species do not occur (i.e., absence data). If data on
environmental variables are not available, then life history traits (e.g., perennial vs.
annual, presence of rhizomatous roots, seed mass, etc.) should be included in the
lists. If the program goal is to implement management based on a prioritized list of
species, then data on life history characteristics, tendency to be invasive in other
geographic regions, known ecological impacts, and feasibility of control are highly
desirable. Older species lists (e.g., > 20-30 years) can be useful in documenting
occurrence of a species in an area, but data on environmental conditions associated
with them may be obsolete.
2.4.2 The Prioritization Process
If species lists exist and resources to evaluate them are available, then the suite of
species that early-detection should most optimally focus upon can be developed
using a process known as prioritization (Fig. 2.2). The prioritization process ini-
tially requires more of an obligation of time and resources than do generalized
monitoring methods, but this investment results in monitoring plans of greater effi-
ciency focused on smaller areas (Fig. 2.1) that can be more cost-effective in the
long run (Fig. 2.3).
The prioritization process has been typically applied to reduce the number of spe-
cies targeted for active management, but it can also be used to reduce the number of
species targeted for early detection monitoring. In both cases, prioritization addresses
