In Robert Frost's poem, "Desert Places," the symbolism used seems to be that of nature, specifically snow, to represent a separateness or loneliness as the world becomes covered, blanketing not only what is seen, but what is heard as well, giving one the sense of being isolated or cut off from the world.
As the snow falls quickly, so does the night, adding to a sense of isolation. The snow is all-encompassing, much as loneliness is: the poem reflects that it covers the last vestiges of growth in the fields, and even the lairs where animals sleep or hibernate. Frost indicates that it will get worse before it gets better:
And lonely as it is that loneliness
Will be more lonely ere it will be less--
The snow represents not only loneliness, but later in the poem it seems to also symbolize the inability of one to communicate because of that loneliness.
With no expression, nothing to express.
However, whereas Frost comments on the snow and how it represents loneliness, he (sadly) holds the "trump" (winning) card. He explains that no matter what kind of loneliness snow may present, he can beat even that. He is not frightened by the aloneness he feels surrounded by snow, or the emptiness of the sky and stars, where no human companionship can be found.
Nature cannot scare him with its quiet snow or quiet night: Frost admits that he is already frightened by the "desert places" that live within him every day; by comparison to those places, the world of snow is no match for his reality.
I have it in me so much nearer home
To scare myself with my own desert places.