According to this chart on Sunray_be's page:
http://www.freewebs.com/dominions2/sites.xls
The Glen of Verdant Greenery is a N1 only site. Could be out of date I suppose. But the Version on Arryn's site says the same thing.
Either the properties of this site have been altered in a recent patch or somehow your first mage was not functioning as a Nature magician at all.