Area covered in “flowers”

Model : flowers1
Simile version : 3.1+
Date added : 2003-06-26
Keywords : Area (modelling changes in) ; Vegetation dynamics ; Lumped model ;

Description

This models the spatial spread of vegetation over an area. Here, the vegetation is taken to be “flowers”. This is not a spatial model in the usual sense where space is divided up into discrete units. Rather, the area covered by the flowers is represented by a single state variable, with an inflow representing increase in area (spread), and an outflow representing decrease in area (death of flowers).

Diagram

Equations

Compartments:
	area of flowers
	Initial value = 10
	Rate of change =  + growth + decay
	Comments: hectares (OK, Ford says acres, but we are in the 21st century now).

Flows:
	decay = area_of_flowers*decay_rate

	growth = area_of_flowers*actual_growth_rate

Variables:
	actual growth rate = intrinsic_growth_rate*growth_rate_multiplier
	Comments: dimensionless

	fraction occupied = area_of_flowers/suitable_area

	growth rate multiplier = graph(fraction_occupied)

Parameters:
	decay rate = 0.2
	Comments: Proportion decaying (per year)

	intrinsic growth rate = 1
	Comments: I.e. 100% per year

	suitable area = 1000
	Comments: hectares (see 'area of flowers'...)

Results

These plots illustate changes in the flows, growth and decay, and the resulting net impact on the area of flowers.

References

Ford, A (1999) Modeling the Environment.
Island Press. p.58

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