The spruce budworm crawls upon and consumes the leaves of coniferous trees. Excessive consumption can damage and kill the host. The budworms themselves are eaten primarily by birds, who eat many other insects as well. The budworms prefer larger trees. A key factor in determining the spruce budworm population is the leaf surface area per tree.
Larger trees have larger leaf surface areas, resulting in larger spruce budworm populations.
The Canadians had observed that the spruce budworm population underwent irruptions approximately every 40 years. For unknown reasons the budworm population would explode, devastating the pineries, and then return to their previous managable levels. The loss of timber represented a significant cost to the Canadian wood products industry and various management techniques, pesticide application, for example, were tried without success. As is often the case in real world modeling, the models became simpler as the researchers learned which processes were critical to the dynamics of the system and which could be removed from the model without seriously affecting it usefulness. The simplest of these models is a single species model, measuring only spruce budworm populations.