Hummock tops alone let trees establish by raising roots above saturated peat

Evidence

The hummock tops are often dry enough that Sphagnum can no longer live there, and other mosses will colonize. These high hummocks provide the only spots where trees could get established, with their roots up above the saturated peat. You see little seedlings of tamaracks and spruces perched on top. A few of them actually succeed, and begin to form an open bog forest. Another group of Sphagnum species flourishes under these trees, where the peat is deep and solid. — Robin Wall Kimmerer, Gathering Moss, 475

Categorization

• ADDENDUM: Relevant to the trees-as-infrastructure theme: moss hummocks act as the scaffolding that lets trees colonize a bog — vegetation-engineering-vegetation sequence.