Which image in the poem "Sonnet 97" conveys nature's bounty?

In "Sonnet 97" the speaker is lamenting being separated from his beloved. To be apart from her for so long feels like the cold of winter. And yet they first parted during the summer, a time of great beauty and the full flowering of nature's bounty:

Yet this abundant issue seemed to me
But hope of orphans, and unfathered fruit.

"Abundant" means something that exists in large quantities, so the speaker's referring here to the fruits of nature. "Issue" in this particular context means something produced. Here, nature has produced her summer fruits in abundance. But the speaker's not remotely interested in any of that. He's still longing for his beloved; indeed, he's pining for her so much so that, to him, the bounties of nature no longer mean anything:


For summer and his pleasures wait on thee,
And thou away, the very birds are mute.



The pleasures of summer are nothing without the presence of the speaker's love by his side. One season changes imperceptibly into another, yet they might as well all be winter, so terribly sad and bereft is the speaker without his love.
https://www.poetryfoundation.org/poems/45101/sonnet-97-how-like-a-winter-hath-my-absence-been