The process by which a state variable (e.g. vegetation composition) modifies the environment in a way that is beneficial for itself. (From Kéfi 2008, Ph.D. Thesis, p.15.) If a system includes a feedback, a series of mechanisms that form a loop is observed. The feedback is positive when a change in a state variable leads to another change of the same sign, as a consequence of the loop (i.e. a variable increase leads to a further increase). In drylands, for example, it has been observed that vegetation can modify the environment in a way that is beneficial for itself.