The pergola was constructed in 2008 at a cost to the Generalitat Valenciana of 3.1m euros and consists of steel arches covered with planks of wood. Originally the wood chosen for the job was Argentine kebracho but that proved to be too heavy for the steel arches to bear and so iroko was specified.
African iroko is a hardwood that is known for its resistance to bad weather so it is puzzling that the wood on this particular pergola has deteriorated so much in just five years.
The answer is simple. The actual wood used was fir because that is three times cheaper than iroko. Even laminated spruce would have been a better choice but no, they used fir. Further more, the wood was not properly treated when it was installed.
If the company that completed the work had used iroko then it could have been restored by sanding the wood down followed by a treatment with oil. Now it looks like all the wood will have to be removed to restore it.