"DaveDay34" wrote in message
...
Lichen usually appears on plants that have a slower than normal
growth rate.
Pruning some trees/shrubs can encourage new growth and the remaining
lichen can
be left to its own devices. It won't do any harm. It is however a
useful
indicator of how fast your trees/shrubs are growing.

Dave.

You should be glad to have lichen in your garden - they only grow in
clean air :~)

http://www.ace.mmu.ac.uk/Resources/F..._4/Air_Polluti
on/19.html

Jenny