Over the course of my PhD program, my research focuses on studying the resilience of ecosystems, i.e. their capacity of recovery after a perturbation. How can the resilience of a complex object such as an ecosystem be measured ? Which variables underpin this resilience, and in particular how do ecological interaction networks play a role ? I investigate these questions by using a mixed approach involving mathematical modelling and an observational approach in the arid steppe of La Crau, France and Yosemite National Park, California.