Remove the Doviello bonus yields, and add a new improvement, available to everyone, on tundra. Possibly ice. Thinking no more than 1 2... something minor, but buildable under forests like camps. Using the temple art from the newest Fantasy Pack.
How about instead of removing the Doviello bonus yields on tundra they get an extra penalty in desert and jungle. Removing the bonus in tundra really steals some of their flavor and unique (well, Illian too) ability to survive in harsh, cold climes. Either that or they should get a bonus from the camps or possibly build them faster.