IN THE MODERN NATURAL SCIENCE OF ECOLOGY the principle of dispersal is closely tied to the principles of competition and succession. In any ecological community, competition is always present. It may be “intraspecific, between individuals of the same species, or interspecific, between individuals of different species” (Stiling 240). It can be “resource competition” involving organisms (most often invertebrates) competing for limited resources, or it can be “contest competition” involving individuals or groups (most often vertebrates) harming one another directly by physical force in a struggle to secure the best territories (Stiling 240).

Each type of competition can be part of the process of succession, which in nature is “the process by which organisms re-colonize an area following a disturbance” such as fire, storms, grazing, or erosion (Stiling 479). In primary succession, plants or animals invade an area in which there were none before, such as a desert or the newly dug pond at Sleepy Hollow (Stiling 479). In secondary succession, one species replaces another already existing species after a disturbance. For instance, when a forest is cleared to create farmland and the farm field is eventually abandoned, the species of trees that repopulates the field might be quite different from the trees that were originally there (Stiling 479).

“The Succession of Forest Trees” and Racial Science

Thoreau's classic description of secondary succession is in his notes on forest succession in his “Dispersion of Seeds” manuscript, which are sometimes published as a separate essay titled “The Succession of Forest Trees.” Thoreau is approached by a farmer for whom he is surveying woodlots who asks “if I could tell him how it happened that when a pine wood was cut down an oak one commonly sprang up, and vice versa” (Faith 104). Thoreau, having observed just that phenomenon recently, has a ready answer: