What are these pom pom trees?

Question

They seemed to be everywhere in Normandy this March. As far as I could tell, these are growths of leaves, not foreign objects like nests (besides, there are so many of them!).

Answer 1

Oh cool! I believe you are looking at a colony of Viscum album (European mistletoe). They are hemiparasitic, meaning they are parasites on the host plant while still photosynthesizing themselves. They really stand out when the host loses its leaves.

Figure 3. Viscum album growths after host leaf-fall.

_{Mistletoe, Viscum album (Santalaceae), in Britain and Ireland; a discussion and review of current status and trends}