I was making an experiment to check how important terrain is for underground tree+plan farming.
Short answer:
The terrain doesn't seem to make any difference at all.
Long answer:
I was running the last version of Masterwork Version 1.9.5 for DF 34.11.
All test are run for 1 year, preparing the plots first and breaching all 3 caverns at the same time.
First I run a fortress with 10x10 plots. 1 for each of these:
-dry clay
-muddy clay
-dry sand
-muddy sand
-mudd rock
-dry clay with canal (11x10 plot with a 1x10 canal in filled with 7 water in the middle)
-muddy clay with canal
After this study results seemed very unclonslusive to me, except for the fact that canals really seemed to have no influence at all, so I ran a second test, this time with 8 10x10 plots for each of the above terrains. Note: I made sure not to dig under any of the plots in both experiments, just in case. So the possible influence of this is not meassured yet, but at least it will not spoil the data.
Results:
Experiments1+2 Full grown trees Semi gown trees Plants SUM of trees SUM of trees + plants
Clay Dry 4 77 79 81 160
Clay Mud 6 73 82 79 161
Sand Dry 5 71 74 76 150
Sand Mud 5 80 92 85 177
Rock Mud 7 78 75 85 160
Average (900 tiles) 81.2 161.6
Average per tile 0.090222222 0.1795555556
There is a very high variance in results from one plot to another, even in the same category, which makes the variance found then totaling each group seem rather small in comparison. My conclusion is that the terrain probably makes no difference.