The title "Succession" is a clue. In ecology, it means the way an abandoned field slowly changes as weeds give way to shrubs and then to trees. The poem seems to catch a field in the middle of that process, where nobody is in charge anymore.
The speaker looks at the land and sees it as "tangier" and "out of order," a word that suggests tangled, snarled growth, maybe with a hint of sharpness or tang. The tone is observant rather than angry or sad. Calling it a place "never likely to thin" suggests thick growth that won't be cleared or tidied, and the speaker seems to accept that, even admire it.
The last lines, "all gone off / and up," are the most open. They could mean the field has gone wild, or that growth is climbing skyward, or that the old order has left. The short, scattered lines give the poem a quiet, slightly wistful mood, with a sense of nature taking over.