index Drain Logistic Compete Coop Exclus Interact Oscillat Preypred Netprod
Openaq Pulse Saltmrsh Prairie Fire Lagoon Climax Species Specarea



Fire is a pulsing model which includes a switch. When the grass has grown up to a critical mass, the fire switches on. When the grass has burned down, the fire switches off. As the fire burns, it releases nutrients which stimulate growth and are bound up in the grass again.


  • Pine forests in southeastern USA, Chaparral in southern California, the Mediterrean...
  • Economic example: a buildup of inventories in a store to a certain amount, followed by a sale to sell most of them.
  • Diagram


    G1, G2 = amount of biomass where fire switches on/off
    TN (total nutrients) = N (nutrients in the soil) + F*Q (nutrients bound in the grass)
    Q = biomass
    K... = interaction coefficients


    N = TN - F*Q
    R = I/(1 + K*N)
    DQ = K1*N*R - K2*Q, IF Q>G1 THEN Q=G2


    The graph shows the changes of N (blue) and Q (green) over a time period. The red lines show the fire.
    Source code:

    "What if" Experiments:

    Think about a forest.

  • Does the forest pulse more or less if more nutrients are added to the system?
  • What happens if the fire is put out by firefighters so that it is stopped earlier?
  • What happens to the system if the fire is kept out completely?