I daresay the the two blokes in the cherry picker will be trained for working at heights and operating the picker, two are needed as no doubt the planters weigh a lot, the two blokes on the ground appear to be council gardeners, presumably responsible for planting them up, transporting them from their yard to the location and telling them how they should be orientated etc, again two because of the size, the last bloke a watchman I would hazard stopping the idiots form walking underneath etc as stupid Joe public has a habit of doing so it seems about right to me H&S wise.
As to whether its right that public money is spent in this way is another subject.