On land, the vegetation determines in large part the distribution of other living organisms. An understanding of vegetation history is crucial for understanding present-day terrestrial ecosystems. The vegetation is made up of several overlapping components, influenced to a greater or lesser extent by historical events. There might be relictual species that have survived from the distant past, a selected assemblage of species that survived the many relatively rapid changes in climate experienced from the beginning of the Pleistocene Ice Ages and also species that have responded more recently to the disturbance brought about by human beings.