So, the thing is that Ancient Savo world map data structures were designed to handle pristine wilderness, and slash-and-burn agriculture. Early on I coded algorithms to simulate how abandoned agricultural lands gradually turn back to forests. But now we have sheep, and grazing animals make it more complicated, as they don't only eat the grass, but also feed on tree saplings. A part of me would like to simulate it down to the details; tracking the age of every tree on every map tile. To manage memory consumption I figured out a way to store all the necessary tree data with 64 bits per tile - but then, storing data in highly optimized bit fields would make all the tree-related stuff solidly hard-coded. And I'd love to keep the game modding-friendly (also, having a feeling that one day Ancient Savo code could be extended and reformatted to create something like a Survival Game Construction Kit). OK, well, so more planning, more alternatives to consider. I'm not yet sure, but the solution might be to have something like "sparse , normal, dense" versions of different woodland types, and then a set of rules to determine if a meadow tile will grow a little, some or a lot of tree saplings. That leaves me wondering if a sparse forest should eventually turn to a dense one (for example, in case there are no animals grazing the grass layer of the said sparse woodland tile). Back to working with pen and paper...