Hi all! Found nuances with animated trees. If set the value defaultstatic = 0 then animspeed=XX starts working!
And even more: if animated trees have defaultstatic = 1 their animation plays fast like mad
(which actually made me look for ways to change the animation speed of trees).
My conclusion: for animated plants need to set value defaultstatic = 0 in fpe.
But, I do not know how this will affect performance. On ~300 trees, I did not notice the difference between defaultstatic=0 and defaultstatic=1
However, in any case, I think this way is better than modifying the tree - making 1600 frames of animation in fragmotion (inserting 3 frames after each 1 original frame) to slow the swing speed
Thanks to
Lafette II for his free trees: it was in their .fpe that I discovered the value defaultstatic = 0 and was puzzled, what motivated me to test on stock plants.