Sadly the front/carved section is susceptible to rot, but I couldn't really put any preservative on it, as the rear section is still growing. I'm slowly training the regrowth upwards to form a shaded canopy over the seat. I guess that over time the seat back will decay, but I'm sure that by this time, I'll have completed a similar carving.
Many thanks also for the suggestion regarding my signature. I have duly changed it.