I did use DFHack fixdiplomats/merchants command, so yes, it was the logging operations that did it. The conversation with Elf diplomat is hilarious, btw, they are quite arrogant!
I modded wood to have steel properties for now (apart from weight, i don't want my kapok bins to weight 50 times more suddenly). Still waiting for another ambush, though. If that won't work enough i'll try something else (can't mod entities, since it's ongoing fort). Modding Elf attributes sounds easy enough for me to do it, magic is outside my capabilities.
Btw, i had the most pathetic goblin siege. 10 goblins? Seriously? Their ambushes were a lot more dangerous... (that's first siege for that fort)