With the introduction of the new model for tree growth quite a while back, things have become somewhat complex. For most players it's sufficient to look at the editor or use the rule of thumb (the greener the better for tree growth) to get a good idea where trees will grow well enough. For map creators and obsessive optimizers though it can be quite difficult to asses what terrain would be optimal to use. So it would be interesting to know a bit more about how stuff works.

So far I have caught that

- every terrain has specific values for fertility, humidity and temperature and each tree has preferences for these values plus a pickiness, and the probabilities shown in the editor are calculated from these values (and how well they match)
- for nodes with different adjacent terrains the vales are averaged (and growth probabilities might be vastly different than for any of the terrains alone)
- foresters plant one of the six trees that grow best on the given terrain
- the probabilities of choosing a tree to plant out of these six are not evenly distributed but weighted

The questions I have now:

- If less then six trees can grow on a terrain, are only those considered by the forester? So on dry soil only Borassus and Coconut Palm would be planted?
- Are the probabilities for planting weighted with fixed values? Or by the relative portion of the sum of all six growth probabilities? Or something else?

Also, things are getting really crazy when you would like to know how well trees might grow on mixed terrains. Since I plan to remake the map for the second mission of the barbarian campaign it would be really helpful to know about suitability of mixes for trees. It uses a mix of terrains around the allowed area for playing that doesn't support buildings but is suitable for a thick forest. I'd like to keep this idea but I'm not sure if I can find out which terrains might work best, as the current choice of Beach (winter) and Tundra 2 is not so optimal. The forest on it gets quite some holes over time from dying trees.