queenrhaenys

The Children carved the faces to awaken the trees.

I don't know where this empowering by blood sacrifice idea comes from..There is absolutely no evidence of that . Bran sees an ancient sacrifice, to which he spontaneously says "No, don't" ..and he says it while connected to the "weirnet" . If he could taste the blood , don't you think he could sense the sentiments of all the other greenseers ? He shares Summer's senses and emotions while warging.

Right at the beginning of AGoT , he learns not to look away ; to be impassive when watching the king's justice being done by Ned. If the sacrifice was the old gods' justice or something demanded or needed or desired by them , I think Bran would sense it . I think he would get a sudden sense of power from it ,if it empowered the tree.

ETA: But Bran's "power" is in his own blood. That's what makes him a warg and ( even more rare) a greenseer. The same is true for all the other greenseers and I would bet the same is true for the trees .

So, there probably is power in some kings' blood. Blood magic works because magic is real ... but I don't think the trees/old gods want or need blood sacrifice.

I would think the same. If the old gods needs blood sacrifice, Bran should have felt the power...well maybe he did, but he's just preoccupied/distracted with whoever was the blood sacrifice he witnessed.