Bark pH and Its Influence on Lichens and Vegetation: Insights from Tristan Gooley

Each tree's bark will have its own pH, and some are more acidic than others.

Larches and Pines are notoriously acidic; Birch, Hawthorne and Oak are acidic too, but slightly less so.

Rowan, Alder, Beech, Linden, and Ash are little less acidic again, and Willow, Holly and Elm are getting closer to neutral. Sycamore, Walnut, and Elder are alkaline.

The less acidic the bark is, the more growth you are likely to see from colonizing plants and lichens.

Pine bark is often bare, whereas Sycamore might have a glorious guest hanging off its bark.
— Tristan Gooley, New York Times Bestselling author, The Lost Art of Reading Nature Signs, Bark