Guy Davenport at The New Criterion:
What “The Dispersion of Seeds” establishes is that Thoreau was inventing the study we now call ecology—how nature keeps house. In France at the same time that Thoreau was plotting how individual trees have their seeds distributed by squirrels, birds, wind, snow, rain, and a free ride on human trousers and skirts, Louis Pasteur was disproving the age-old belief in spontaneous generation.
Even though the introduction by Robert D. Richardson, Jr., places this text historically and biographically, showing how it reflects Thoreau’s acceptance of On the Origin of Species over his allegiance to Louis Agassiz’s theory of repeated cataclysms and geneses, there is a deeper dimension to Thoreau’s text. At the center of his detective work is Thoreau’s observation that pine seedlings thrive best in stands of oak, and vice versa: exactly the opposite of what one would expect. Thoreau sees in this a cunning arrangement whereby if an oak forest goes down to a forest fire or the axe, a pine forest is there ready to replace it. But he does not have the knowledge of soil chemistry to account for why pine seedlings fare better among oaks than near their parent trees. It was in the reforestation of Jutland that the Danes discovered that the mountain pine (Pinus montana) seemed to be dependent on the proximity of spruce (Pica alba), neither of which grew into healthy trees without the other. A Colonel E. Delgar established this mutuality as a principle, and thus reforested large areas of a country that was being taken over by sand dunes. I suspect that Thoreau had discovered a similar relationship of interdependency far ahead of botany’s ability to account for it.