Larch roof on the gazebo, ageing gracefully?

Larch is a wood valued for its tough, waterproof and durable qualities; top quality knot-free timber is in great demand for building yachts and other small boats, for exterior cladding of buildings and interior panelling. The timber is resistant to rot when in contact with the ground, and is suitable for use as posts and in fencing.
This roof was erected twelve years ago, and it has attracted increasing numbers of lichens in our clear air.