Herb
First tree back onto bare ground — the broom, the beginning, the clean slate.
These are associations the community holds, not settled fact — the more a reading is shared, the bolder it sits.
Birch is a coloniser. It seeds onto burnt, cleared or abandoned ground faster than anything else in northern Europe, grows quickly, dies young and makes soil for the trees that follow. Every association it has picked up follows from that: beginnings, renewal, the first month of the Celtic tree calendar in Robert Graves's much-loved and largely invented scheme.
Its practical uses run through the same idea of clearing. Birch twigs make the besom — the household broom of English tradition, birch brush on a hazel or ash handle — which is why the tree sits at the root of an entire genre of witch imagery. Birch was also the schoolmaster's rod and the magistrate's, and it is worth being honest that the tree's cleansing reputation includes a strand about corporal punishment that we would not now describe as cleansing.
The bark peels in white papery sheets and is nearly waterproof, having been used for canoes, roofing and writing across the whole northern world. Birch sap is tapped in spring in Scandinavia and the Baltic, which is a real seasonal practice rather than a folkloric one.
Readings practitioners have offered, ordered by how many recognise them. Take what serves, leave the rest.
Carried forward
English household practice
The besom is birch brush bound to a handle of hazel or ash, made for sweeping and replaced when it wore out. Its role in craft as a tool for clearing a space is an extension of a real object that was in every kitchen.
Carried forward
Nicholas Culpeper, The Complete Herbal (1653)
Culpeper gives the birch to Venus and notes, drily, that it is a tree of no great use in physic but of considerable use in correcting children. He is describing the birch rod, and he clearly thinks the tree is wasted on it.
Credit what you carry. Much of this comes from living traditions, and some of it from traditions that are closed — held by particular peoples and not offered for general use. Where you know whose practice a reading came from, name them; where you don't, say that too.