Excitable media
Temporal oscillations also occur in excitable media. To understand this concept, consider a forest fire. We start from a forest with fully grown trees. If the forest burns, trees will be destroyed. Fortunately, new trees will soon start growing and after many years the forest will be more or less back to its original state. It will then have undergone a full cycle. If a new fire is set, this pattern will repeat itself and we will then have periodic oscillations of the forest between a burnt state and a “recovered” state in which all of the trees are fully grown again.