I don't know either!
I guess this is a styrofoam ball covered in roses..
I've done a foam circle cut in half to form a dome ,cpvered in fondant and attached roses to that.
Or molded a peice of foil to the shape I needed it, covered it fondant and used that.
I, too, use a styrofoam ball or foil formed into a ball.
Here are ones like the photo roses that I have done. The pink one, I used a piece of styrofoam and the red one I just put together by hand like a bouquet of flowers. I actually found that by hand was easier and looked better (a tighter ball).
We'll I can't get them to attach, but they are in my photos.
Some good methods listed above, but whatever method you go with make sure you put enough support on the top tier - that bouquet can get heavy.
If you look in my pix, Megan's wedding cake, I did a topper very similar to this. I cut styrofoam to look like a 4 inch cake dummy and made the roses from gumpaste. We didn't have any extra supports or anything that I recall for the topper - it was sitting on top of a 6 inch cake.
thank you all so much! i really want to create this look and i think everyone has given me some great ideas. cant wait to do this!