Okay, so how would you rule this situation:
A druid casts Diminish plants on a giant tree that an enemy is on. Specifically the prune growth version of the spell which is described as follows:
Prune Growth: This version of the spell causes normal vegetation within long range (400 feet + 40 feet per level) to shrink to about one-third normal size, becoming untangled and less bushy. The affected vegetation appears to have been carefully pruned and trimmed. This version of diminish plants automatically dispels any spells or effects that enhance plants, such as entangle, plant growth, and wall of thorns.
At your option, the area can be a 100-foot-radius circle, a 150-foot-radius semicircle, or a 200-foot-radius quarter-circle. You may also designate portions of the area that are not affected.
Now to me, the spell seems like it is meant to be used on brush and vines and stuff to clear the area, though the druid was apparently intending to sever the branch the enemy was standing on. I am not entirely sure a tree counts as "vegetation" based on the description. I ended up meeting halfway and saying the tree shrunk to 1/3 size and gave the opponent a reflex save to avoid falling off.
How would you all rule it?