Alternation and Coexistence of Tree Species

In virgin forests, individual trees tend to be succeeded in time by those of another species. The phenomenon was recognized by a French forester and named "alternation of species" as early as 1905 (Schaeffer and Moreau 1958). The process is frequency dependent, not only setting the ratio of two species but driving the community toward equilibrium. The causes of alternation, some probably related to density regulation and some not, can all operate at the size scale of single large trees, excepting, of course, dispersal. Trees themselves serve as microhabitats for seedlings and saplings, and that is sufficient for mediating tree coexistence.