"dynamics are" because the word is plural.

I dropped "very" because it wasn't in the German sentence.

Here's where it gets a little complicated. :-)

If you use "Group Dynamics" as the name of a field of study, then "is".
-Group Dynamics is a fascinating area of research.
But normally,
-Group dynamics are important when considering how to structure your team.

Thanks a lot, Robert! I felt there were exceptions where you say "Group dynamics is".
Well explained :-)