Fecundity has to do with fertility not just literally but in a figurative sense as well. So it could refer to a lush valley and equally so to the rich vocabulary in a story. Biologically speaking, fecundity refers to the potential of having offspring as opposed to fertility which refers to having offspring itself.
Some instances of the word in literature:
“Along with the mystical wonderment and sense of ecological responsibility that comes with the recognition of connectedness, more disturbing images come to mind. When applied to economics, connectedness seems to take the form of chain stores, multinational corporations, and international trade treaties which wipe out local enterprise and indigenous culture. When I think of it in the realm of religion, I envision smug missionaries who have done such a good job of convincing native people everywhere that their World-Maker is the same as God, and by this shoddy sleight of hand have been steadily impoverishing the world of the great fecundity and complex localism of belief systems that capture truths outside the Western canon. And I wonder—if everything’s connected, does that mean that everything can be manipulated and controlled centrally by those who know how to pull strings at strategic places?”
“Mrs Ramsay, who had been sitting loosely, folding her son in her arm, braced herself, and, half turning, seemed to raise herself with an effort, and at once to pour erect into the air a rain of energy, a column of spray, looking at the same time animated and alive as if all her energies were being fused into force, burning and illuminating (quietly though she sat, taking up her stocking again), and into this delicious fecundity, this fountain and spray of life, the fatal sterility of the male plunged itself, like a beak of brass, barren and bare. He wanted sympathy. He was a failure, he said. Mrs Ramsay flashed her needles. Mr Ramsay repeated, never taking his eyes from her face, that he was a failure. She blew the words back at him. “Charles Tansley… ” she said. But he must have more than that. It was sympathy he wanted, to be assured of his genius, first of all, and then to be taken within the circle of life, warmed and soothed, to have his senses restored to him, his barrenness made furtile, and all the rooms of the house made full of life—the drawing-room; behind the drawing-room the kitchen; above the kitchen the bedrooms; and beyond them the nurseries; they must be furnished, they must be filled with life.”