by Fichina » Fri Apr 15, 2011 10:51 pm
Deforested forests degrade into grasslands, which degrade into moorland and further into heath so long as there one already existing tile of the next degradation around. Which can be done by plowing.
Forest won't degrade directly into moor or heath, so those little squares of forest in your growing moor/heath creep take a while to change.
Artificially placed grass will degenerate to normal grasslands if there's grasslands around. It will also naturally revert back to whatever tiles surround it, but this seems to take far longer. A patch of artificial grass surrounded by stone/brick will never revert naturally without plowing
Tiles that are stomped to dirt will revert back under similar rules, but this seems to take even longer than the grass. Mudflats don't follow these rules, but will if you stomp them to dirt first. Dirt can revert to artificial grass, but not stone/brick.
Planting trees can generate random tiles of the tree's native forest habitat, but they'll revert to grassland if the trees are removed. Forest tiles never creep.
Nothing will ever degrade to swamp, mountain, thicket, beach, mudflats, artificial grass, or stone/brick
Swamp, mountain, thicket, beach, and mudflats cannot degrade into anything by creep, but can be overwritten by tree tile generation. If it can be plowed/paved it can also be overwritten by stone/brick/artifical grass. These are limited resources and in theory could vanish completely from the world if people were so inclined and there was enough time.
Dug out portions of caves will never creep to natural caves and nothing else can be introduced down there.
Water/stone/brick does not creep or overwrite under any circumstance.