Conclusion: Significant impact.
Guess at explanation: Being far enough away from body of water and just right elevation has a significant impact on terrain bonus.
Conclusion: Trees planted four squares away have no impact, but three squares away do.
Guess at explanation: Trees effect terrain bonus with a range of three.
So the conclusion is largely: not worth it to bother with trees, build another or upgrade your current well instead? It’s not practical with that many trees in town for such a low and sometimes no improvement.
One thing this has me thinking about is the water table mechanic. I noticed that areas with better water levels grew more wild trees, and it seemed like I was able to encourage this with decorative trees - plant a bunch of those, they may or may not improve the water table in the area, but if they do, then cut them down after they’ve been there for a while, and that area would thereafter be more likely to produce wild trees.
Your tests might lend to the theory that planting trees in lower elevations = better water table improvement = better wild growth.
I should have noted this was tested on the wastelands biome which is very harsh. It is easier to see differences in the hardest situation. On Arid the areas it will work are much larger, and probably more so again on the even easier biomes.
Also, most of the trees on Well Two aren’t having any effect, just some of them. As the trees were finishing construction I’d occasionally notice one alone improve the well by a couple of percent. Luckily the maturity of trees didn’t seem to matter, so you could tell instantly what the effect was. (@tigon)
So the practical conclusion is; it is worth doing when it works, but you’ll need a bit of trial and error on each well to see if it will.
Could be worth a wee experiment with trying different tree types. I may have a play with that myself… but not with the current map — too bleedin’ busy getting repairs done and prepping for the next raid (and I’m by lakes anyway).
