Habitat characteristics represent the matrix for the evolution of morphological, physiological and behavioural adaptations and life history traits of animals. These include bottom-up factors (such as distribution and abundance of food) and top-down constraints (such as protection from predators). The role of different habitat components in the survival and reproduction of individuals is of prime interest and is relevant for evolutionary understanding as well as for primate conservation. So far, this has been studied by linking habitat characteristics with phenotypic traits of animals, assuming that these traits represent adaptation to a given habitat constraint. However, we should bear in mind that the characteristics we observe today may represent adaptations to constraints that acted in the past (the Epaminondas effect, named after the little boy who always did the right thing for the previous situation; or, in evolutionary terminology: animals are tracking fitness optima by trying to climb the sides of shifting adaptive peaks, Cody, 1974). However, testing hypotheses based on these ‘ghosts of past constraints’ has so far been impossible. The present chapter focuses on the description of the vegetation of forest habitats as the biotic matrix for the evolution of life history traits. References are to textbooks or publications that illustrate applications of the methods and do not always refer to the original work.