What happens to the forest "before the moment of hesitation had given way to action?"

Before the moment of hesitation a tree was struck by lightening, pinning the two men beneath it.

And before the moment of hesitation had given way to action a deed of Nature's own violence overwhelmed them both. A fierce shriek of the storm had been answered by a splitting crash over their heads, and ere they could leap aside a mass of falling beech tree had thundered down on them.