Here is a position statement from the British Lichen Society on Beavers, dated January 2023:

Beaver reintroduction is happening and is likely to have benefits to some aspects of biodiversity.
There are little or no benefits to the international important lichen assemblages of Scotland that mainly depend on stable habitat with veteran trees. There are likely to be significant losses of old trees and shrubs near water bodies/water courses. Beaver activity thus poses a threat to the assemblages associated with old trees/shrubs (especially on hazel, aspen and veteran willow). At the landscape scale, the impact is likely to be greatest in areas where veteran trees and shrubs supporting assemblages/rare lichens are local and concentrated along edges of watercourses/waterbodies.
The BLS views appropriate assessment and mitigation measures to minimise any losses of internationally important lichen assemblages as vital. Monitoring of the impact will be important and the information should be used to devise and inform implementation of  practical mitigation measures.
In Scotland, the BLS was involved with the consultations for Beavers in Scotland: A National Strategy and supports this as the way forward and has signed up to the strategy.