Certain processes in geomorphology are too slow to be wholly investigated in one individual’s lifetime, so the development of such a process may be observed by finding other sites where that process is exhibited at a different developmental stage. In ecology this means that past or future trajectories of ecological systems may be inferred from contemporary spatial patterns (Blois et al. DOI: 10.1073/pnas.1220228110).
J. D. Aber and J. M. Melillo (2001) give an important caveat: ‘this approach assumes that the sites only differ in time and not disturbance or other underlying factors unrelated to time’.