In the six years that had passed since the publication of his Pulitzer Prize-winning collection A Further Range, Robert Frost had become a widower, lost his son Carol to suicide, and had begun to rebuild his professional life with the help of fellow writers and his personal secretary Kay Morrison. In 1942, as the United States entered World War II, the sixty-eight-year old Frost produced a collection of poems that portrayed the power and beauty of nature using language that drew on a lifetime of accumulated knowledge.

Arguably the most important scientific development in the years preceding the publication of A Witness Tree, was the discovery of nuclear fission by German radiochemists Otto Hahn, Fritz Strassmann, and physicist Lise Meitner. Their work revealed how the heavy element uranium could be induced to split into lighter elements releasing energy in the process, a finding that led to the development of nuclear weapons. There is one possible reference to nuclear weapons in A Witness Tree in the poem “It Is Almost the Year Two Thousand” when Frost talks of the millennium ending in “a final golden glow,” but nuclear weapons do figure prominently in Frost's next collection, Steeple Bush, which was published in 1947.

In this collection, Frost continues to describe nature and natural processes with great accuracy and artistry; but now he moves beyond simple appreciation and asks questions about man's place in nature. In the poem “The Lesson for Today,” Frost likens humans to a biofilm on the surface of the earth and laments the regrettably short time each of us has to accomplish something while we are here. Similarly, in the poem “Our Hold on the Planet,” he suggests that, although we are really just a thin shell around the earthly sphere, there must be some slight advantage that has allowed the human race to survive. In the poem “A Considerable Speck,” he appreciates that a tiny mite crawling on his piece of paper provides at least some evidence of intelligence since he cannot guarantee that his own contributions to the paper will.

Frost also writes of natural processes in a way that puts man in his place, reminding him that he is a relative newcomer and a rather unimportant one at that.