381STSMs can help land managers determine appropriate strategies for resource
allocation, including selection of management activities and locations. For this
example, we draw upon a recent study of a non-Bromus invasive grass, Pennisetum
ciliare (L.) Link (buffelgrass; synonymous with Cenchrus ciliaris), by Frid et al.
(2013b) in the Sonoran Basin and Range, which demonstrates an application that
could be applied in future work to Bromus. In this model, the phases distinguish
between P. ciliare abundances (<5 %, 5–50 % and >50 % cover) and whether they
are detected or not (Fig. 13.2).
This model was a spatially explicit STSM, developed using TELSA (Kurz et al.
2000 ), which included input and output maps of the P. ciliare over time, and distin-
guished between detected (and treatable) and undetected patches that would require
resources to be detected. The model simulated dispersal of short- (i.e., neighbor-to-
neighbor) and long-distance dispersal of P. ciliare to other locations on the land-
scape based on time series of spread determined from aerial photography (Olsson
et al. 2012 ). A map of the current known distribution of P. ciliare was derived from
the same aerial photographs. A habitat suitability model based on slope, aspect, and
elevation was used to estimate where P. ciliare could grow, and at what densities.
Fig. 13.2 State-and-transition model used by Frid et al. (2013b) to simulate alternative manage-
ment strategies for P. ciliare in southern Arizona. The STSM categorizes each spatially explicit
polygon dynamically over time based on both the presence and abundance of P. ciliare and on its
detection status. The STSM has a total of eight possible states represented by five possible cover
classes (absent, seedbank only, cover <5 %, cover 5–50 %, cover >50 %) and by whether the pres-
ence of live plants has been detected by managers
13 State-and-Transition Models: Conceptual Versus Simulation Perspectives...