December 2012 Number 1 - Utah Native Plant Society

Calochortiana December 2012 Number 1
erally, when threats are poorly known and hard to quantify
given available information, it is recommended that
a conservative (higher) score be used. This element is
scored range wide in this preliminary analysis (Table 3).
5. Climate Change Vulnerability
The climate envelope of a species can be modeled to
predict distributional changes with global warming (e.g.,
Miles et al. 2004). Although we lack data for many species,
a proxy variable that can provide a first approximation
to the vulnerability of a species to climate change is
its elevation range. If a species has a relatively broad
elevation range, populations along the gradient will be
adapted to local climates, and the species genetic ability
to adapt will likely be greater than in a species with a
very small elevation range exposed to a much smaller
range of climate variability. Elevation ranges from
1000 meters are used to score each species
for climate change vulnerability (Table 3).
6. Number of Known Populations
This element in the ranking system is based on the
general concept of element occurrences developed by
the Nature Conservancy and further refined by Nature-
Serve (Faber-Langendoen et al. 2009). The five categories
are the same as the G and S ranks on the various
state and state natural heritage databases, although I
have provided more explicit criteria for the G4 and G5
levels. Species with widespread continuous populations,
such as many conifers, are ranked G4 if found within a
single subprovince, and G5 if they are in more subprovinces.
Thus a widespread species such as Saguaro
(Carnegiea gigantea) is ranked as a G4, despite its large
population size, because of its restriction to the Sonoran
Desert. Since there are slight differences between this
ranking element and the G scale, I have given this element
the letter N for number of known populations. The
scores are inverted from the N rank, thus a N1 is scored
a three, an N2 a two, a N3 a one, and N4N5 a zero.
Table 3. Four additional elements of the scoring system for ranking at-risk species, with scores from 0-3,
and explanations for how each is scored.
Ranking Elements 3-6 Score Explanation
3. Population Trend Historical trends (if known) since approximately 1900, or when the species was
first discovered.
Stable or increasing 0 Populations are secure for the foreseeable future, with trends exhibiting natural
short and long-term variability
Minor declines 1 Data are available to indicate that some declines have occurred, (10% decline in total numbers
per year
4. Direct Anthropogenic
Threats
Scores are typically applied range-wide, although they could be used in a more
narrowly defined region if needed.
No direct threats 0 Few if any impacts from recreation or domestic livestock grazing, no invasive exotics
present, no mining activity, recreational impacts largely absent, etc.;