From the title to the last sentence, Saki's classic short story holds that man is an unwanted presence, an intruder, in nature. In the context of the recent Great War (WWI), in which Saki was a soldier, man's fight to possess land as a by-product of nationalistic greed was his downfall.
From beginning to end, the story characterizes man as a lame duck in a hostile environment:
In a forest of mixed growth somewhere on the eastern spurs of the Karpathians, a man stood one winter night watching and listening, as though he waited for some beast of the woods to come within the range of his vision, and, later, of his rifle. But the game for whose presence he kept so keen an outlook was none that figured in the sportsman's calendar as lawful and proper for the chase; Ulrich von Gradwitz patrolled the dark forest in quest of a human enemy.
The irony, of course, is that these men will not be killed by human enemies, but by the "beasts of the woods" foreshadowed in the first sentence.
Later, more nature imagery relates to human death:
Both had now given up the useless struggle to free themselves from the mass of wood that held them down.. But what a Heaven-sent draught it seemed! It was an open winter, and little snow had fallen as yet, hence the captives suffered less from the cold than might have been the case at that season of the year; nevertheless, the wine was warming and reviving to the wounded man, and he looked across with something like a throb of pity to where his enemy lay, just keeping the groans of pain and weariness from crossing his lips.
These men have been exploiting nature for years, and it finally gets revenge in the end. The tree's attack is reminiscent of Birnam Wood coming to Dunsinane Hill in Macbeth (nature takes revenge on Macbeth). These two have taken nature for granted for so long that they underestimate its destructive power.
"Who are they?" asked Georg quickly, straining his eyes to see what the other would gladly not have seen.