Three short lines hold a quiet moment of looking closely. The speaker is counting rings, the kind you find in a cut tree, to measure age, and doing it beside a wood frog pond. The final line, "another year," works in two ways. It could be the count itself, arriving at one more year added to the total. It could also be the speaker's own sense that yet another year has passed, with the pond and the wood around it as the measure.
The poem never says how the speaker feels, which is part of its charm. Judging by the plain, unhurried wording, the mood is calm and contemplative, with a hint of wistfulness. There is no alarm about time passing, just a patient noticing. The pond is small and the act is small, but the poem suggests that nature keeps its own record, and that paying attention to it is a gentle way of understanding how time moves, for trees, frogs, and the person standing there.