Vegetation and Disturbance - Environmental Modelling: Finding Simplicity in Complexity - page 236

The good fit between the regressions based on real
data (Figure 14.2) and the outputs of both the process-
based model (Figure 14.4) and IBM (Figure 14.5) are
evident, but in this case the curves are characterized by
oscillations due to the mortality and birth processes of
individual plants.

run was extended to 30 years in order to investigate
longer term successional behaviour (Figure 14.6). In this
case, without grazing, Rubus shows an initial dominance
followed by a decline due to its sensitivity to competition,
whereas Erica and Ulex can shift their final dominance in
relation to the grazing pressure.
The application can be further extended both in time
and space to show the system capability to upscale local
(pixel) functional dynamics, integrating them with other
landscape-level processes. A schematic representation of
the vegetation model linked to pixels of the spatial raster
system is shown in Figure 14.7a. Results of a simple
simulation exercise show the emergence of spatial pat-
terns of species dominance related to both the grazing
pressure and initial density conditions (Figure 14.8). Such

Extended applications
In contrast to empirically based regression models, the
process-based models can be applied to simulate longer
term dynamics. To show this concept, another simulation
of the system dynamics model of plant regrowth after fire
was carried out with equal initial biomass for the different
species; this removed the competitive advantage due to
the higher initial density of Erica species. The model

Vegetation
thickness Palatability

Slope

Vegetation

Animal
distribution

Vegetation

Vegetation Growth

Grazing pressure

Vegetation Growth

Biomass

Fire

Biomass

(a) (b)

Vegetation
thickness

Palatability

Slope

Animal distribution

Wind direction Wind speed

Vegetation

Grazing pressure Seed production

Seed dispersal

Vegetation Growth

Seed distribution

Fire

Biomass

(c)

Figure 14.7 Schematic representation of modeling workspaces: (a) simple link between SIMILE n -species model with raster system.
(b) integration of animal distribution model with pixel level vegetation model. (c) integration of two spatial processes (animal
distribution and seed dispersal) with pixel-level vegetation model.