Solutions to the questions for model

Grass reproduces more rapidly than the shrubs. Yet, it is competitively inferior to the two shrub species so that its propagation and maximum population density are progressively reduced by increasing shrub cover until the system becomes shrub-dominated. Growth is not unlimited, so for each species there is a maximum number of individuals which can grow in the vegetation section shown in the model.

Repeated fires change the vegetation to a grass dominated community.
All plants suffer from mortality due to fire in the same proportion. Mortility increases with fire intensity. As grasses are the fastest to reproduce, they are quickest to occupy the space. Regeneration of the shrubs - and thus the competitive suppression of grasses - is prevented when the interval between successive fires is sufficiently short.

Fires will occur only if there is enough combustible material at the time of an ignition event. The grasses in this model are more combustible than the shrubs. With increasing vegetation density the amount of fuel rises, allowing not only an ignition event to produce a fire in the system, but also increasing fire intensity.

Rules

The grass multiplies by a factor of 1.75 per year, the fast growing shrub (fgs) by 1.3 per year and the slow growing shrub (sgs) by 1.1 per year. Maximal density of the different species is 400 for the grasses, 150 for the fast growing shrubs and 250 for the slow growing shrubs. At the maximum shrub density the density of grasses is reduced to 100 individuals.
The most intense fires can reduce plant numbers to about 10% in the following year.
Each shrub has an ignition value of 1, each grass of 2; the threshold above which an ignition leads to a fire is 350, the max. ignition value of the community is 800 (250+150 for the shrubs, plus 2x200 for the grasses).