Moss and Lichen

 What grows on tree bark?
Lichen, Algae, and Moss on Trees | University of Maryland
Lichen, algae, and mosses grow harmlessly on tree trunks and no control is necessary. They are considered an indicator of good air quality.  Feb 27, 2023

Garry Oak Ecosystem Restoration https://goert.ca/about/what-are-geo/
https://goert.ca/ - Garry Oak Ecosystem Recovery Team Canada.

https://www.columbialandtrust.org/lichenandoak/
The site has some of the region’s last remaining stands of mature Oregon white oaks (Quercus garryana), or Garry oaks, which offer the only known substrate for rare, slow-growing species of lichens. Used as food, shelter, and nesting material, lichens in Pacific Northwest forests are critical for squirrels, birds, deer, bats, and invertebrates such as wasps and butterflies. Lichens are ecological indicators, susceptible to changes in air quality. They thrive in regions of high air quality and can be absent from cities due to air pollution. In forest canopies, lichens can moderate humidity and temperature and enrich soil content, allowing neighboring plants to thrive.