The wood, in which the unnamed man hides from the attacking horse, is presented as a hostile, almost alive presence, providing shelter but also impeding his progress. At one point, while fleeing, he hides:
In blinding rain he lunged through the barricade of brambles at the wood's edge. The little crippled trees were small choice in the way of shelter, but at a sudden fierce thickening of the rain he took one at random and crouched under the leaning trunk.
(Hughes, "The Rain Horse," Amazon.com)
The strong adjectives create a claustrophobic sense to the wood, which seems itself to have been beaten down by the rain. Instead of easily hiding, the man must break through a bramble hedge, and the trees inside are small and whithered, not strong and tall. However, even this uncomfortable place is preferable to the hostile horse; at least the wood does not actively attack him.