I recognize this is not modern times, but anyone have any ideas on rules for reasonable levels of terraforming? Some of the terrains can be converted with enough effort and resources. For example forest can be clear cut, etc. In fact often such can be the result of too much of the wood trade. Just wondering if anyone had any ideas.
The best way to handle this under the current ruleset is by GM fiat, and the GM will need to consider character effort, story goals, and game balance in deciding such a thing. It isn't likely over the course of normal play in Fantasy, only over an extended period.
As a GM, I might rule that the attempt is the same as Enhance County, above and beyond the county's effective maximum based on terrain, and that regardless of roll it only succeeds if I think it's reasonable. I'd only even allow the attempt if the terrain maximum were currently capped, and then yes we'd discuss irrigation in a desert or tree cutting in a forest to determine reasonableness.
Note that in the realm creation and setting conversion rules this is simply arbitrated by the GM, and so I think that in spirit that idea still applies.