Prognosis of new spots initialization of bark beetle is derived from probability of forest stands infestation by bark beetle and from tree mortality.
First the procedure calculate area of current spots of bark beetle. Then the expected area of new spots is calculated by subtraction of current spots of bark beetle and tree mortality. If the mortality is 0.5, then the area of new spots is going to be half of the current spot area.
Cells with highest value in attack probability of forest stands layer are selected so that they total area is equal to area of new spots. New spots will not overlay current spots, because the value of probability was set to zero.