While a branch’s origin on the trunk doesn’t change—one thing I remember answering correctly on my biology SAT test 400 years back—the branch itself may bend and reorient.
Trunks and branches are subject to many forces that change their shape. Some are environmental. And some are of the tree’s own making.
One curious force that the tree initiates is called gravitropism. This is when a trunk has fallen over, as it might from a stiff gale, and the trunk bends upwards to compensate. It does this by growing reaction wood.
What’s fascinating is that angiosperms (flowering plants) and gymnosperms (cone plants) have evolved opposite reaction wood methods.
The angiosperms create tension wood, where the cells on the inside (upper) side of a prostrate trunk contract. Gymnosperms on the other hand create compression wood, where cells on the lower side of a trunk elongate. Both move the trunk into a more vertical position, one by pulling and the other by pushing.
A gymnosperm (a Hemlock) trunk. The arrows indicate the effect of compression wood. Cells on the lower side of the trunk elongate to create growth asymmetry, curving the trunk up.
Let’s imagine this same tree as if it were an angiosperm. The cells on the top of a prostrate trunk have contracted to create tension wood, pulling the trunk upright.
Trunks are not the only places we find such buttressing. Old, heavy branches appear to create reaction wood to prevent breakage.
If all that isn’t wild enough, where reaction wood is built is controlled by graviperception, found in epidermal cells that have an apparatus that can tell up from down. Roughly this is a specialized cell with independently moveable starchy things—imagine an orb half-filled with marbles—and when the orb moves, the marbles reorient. Depending on where they reorient, a physical response is initiated, changing plant shape. Roots and shoots have opposing reactions to this process so the roots don’t grow up and the shoots don’t seek the dark.
So, your tree’s cells can perceive gravity. Which is more than I can do some days.