  In this work, an individual-based model of forest insect outbreaks is
presented. The results obtained show that the outbreak is an emerging feature
of the system. It is a common product of the characteristics of insects, the
environment in which the insects live, and the way insects behave in it. The
outbreak dynamics is an effect of scale. In a sufficiently large forest
regardless of the density of trees and their spatial distribution, provided
that the range of insect dispersion is large enough, it develops in the form of
an outbreak. In very small forests, the dynamics becomes more chaotic. It loses
the outbreak character and, especially in the forest with random tree
distribution, there is a possibility that the insect population goes extinct.
The local dynamics of the number of insects on one tree in a forest, where the
dynamics of all insects has the character of outbreak, is characterized by a
rapid increase in number and then a rapid decrease until the extinction of the
local population. It is the result of the influx of immigrants from neighboring
trees. The type of tree distribution in the forest becomes visible when the
density of trees becomes low and/or the range of insect dispersion is small.
When trees are uniformly distributed and the range of insect dispersion is
small, the system persists as a set of more or less isolated local populations.
In the forest with randomly distributed trees, the insect population becomes
more susceptible to extinction when the tree density and/or range of insect
dispersion are small.
