Complex systems are made up of many individual parts, often simple ones, that work together by following simple rules without anyone being in charge. Because of how these parts interact, the system as a whole can show behaviors and properties that the individual parts alone don’t have.

Compared to complicated systems, complex systems often consist of many similar individuals. The behaviors of the individuals can be broken down into a set of simple rules, based on which the individuals interact with one another without central control. Therefore, complex systems can tolerate adding or removing some individuals, and some complex systems can adapt to these changes. Disorder is an inherent aspect of complex systems, so the same inputs yield different results each time, making the outcome of a complex system cannot be precisely predicted.

The beetle-forest system is complex because it includes similar host trees and bark beetles that interact with each other according to simple rules, leading to emergent outbreaks.

Rising temperatures allow more beetles to survive during the cold months and accelerate their development in the warm months, leading to an increase in the beetle population. Meanwhile, droughts stress the host trees and weaken their defense.

A system perspective may broaden our view of solving problems. The climate-affected beetle-forest system has three main parts: bark beetles, host trees, and climate factors such as temperature and drought. These components interact with each other, which means there are several ways to address the issue by targeting each one individually and their connections. For example, we can reduce the number of bark beetles by removing infected trees, diversifying the forest to prevent monoculture, and taking action to lower CO2 emissions, which can help slow temperature increases.