The tree featured in Betty Smith's inspiring novel A Tree Grows in Brooklyn does not exactly play a role in Francie's growth and development over the course of the text, although this is what the story is about. Rather, the tree is a symbol of the strength and courage it takes for an underprivileged young girl to grow up into a strong, independent, well-educated and self-reliant woman in spite of the unfavorable setting in which she must do so. The novel has been called a story of survival. The tree has the same survival problem. It grows up in a slum neighborhood where it receives no attention of any kind, and hardly any notice. It has to force its roots down through cement into poor soil. It has to survive the cruel New York winters. But it manages to grow tall and beautiful under the harshest circumstances. In the eNotes study guide section on "Critical Essays," the tree is described as follows:
[Betty] Smith asserts that Brooklyn is where the “Tree of Heaven” grows. The tree sprouts in empty lots, trash heaps, and tenements. When Francie leaves Brooklyn, the tree is still there flourishing—a symbol of the human spirit that continues in the face of adversity. Like Francie, the tree survives in a hostile environment. The novel ends as it began. Another eleven-year-old girl reads from the fire escape, and the young adult Francie sees herself in the girl. Smith closes the novel by emphasizing the universality of existence. Just as the scrubby tree sprouts new shoots, new generations of young girls emerge to learn of life as Francie has.
The tree is an excellent symbol for Francie because she is forced to grow up pretty much on her own. She does this mainly through her love of books. She is an ardent reader. Her greatest pleasure, whenever she has the time, is to curl up in some comfortable spot for hours and hours and read books she obtains from the public library. She is a real reader. And anybody who loves to read, as Francie and her creator Betty Smith loved to read, will respond to A Tree Grows in Brooklyn. Nothing really unusual happens to Francie in the story. It is her internal development derived from her addiction to reading that is the main subject of the novel. This development is a slow and nearly undetectable process, just like the slow but persistent growth of the tree.