Have you seen these on the trunks of your trees?
Commonly known as Bracket fungi, arborists generally refer to them as Ganoderma (genus).
They are a clear indication of internal decay that can potentially cause complete tree failure.
The woody-hard, bracket-shaped fruiting bodies, appear mainly on dead wood, but are sometimes also parasitic on living trees and grow up to 60cm across. They are perennial, forming a new layer of tubes each year, like the growth rings of a tree. The lower surface consists of pores. During active growth, this pore surface is white but readily turns brown when touched. Spores produced are often seen as brown dust below the bracket.
Removing brackets does nothing to help your infected tree. The microscopic mycelium within the tree attacks and continues to decay the wood.
If you see these, your tree is likely to be in compromised health. Some trees can live with these for many years, but good advice is needed to establish the stability and safety of your tree.