How could Treebeard call for war without an Entmoot?

In the movie of The Two Towers, there is an Entmoot, in which the Ents decide not to go to war.

Then, after Treebeard sees what Sauruman has done to the forest, he calls for the Ents to go to war.

How does Treebeard have authority to do this without another Entmoot?