these look like fake stems to me... stems wrapped around a post that holds the top tier, with the tops of the flowers pushed into the top of the top tier. Try looking online for a stand like that, that you can wrap the stems around.
You could use Wilton's Tall Tier Cake Stand for that...I think you can buy only the pieces that you need.
if you look at my pictures there is one of a tinkerbell tree... i think the support system i used would work the same way for you.. i formed the tree around the support! it's made by wilton.. i can't remember the name of it but if you want i can look it up later for you. i know all of the information is in the current wilton yearbook.
lol didn't see the post ahead of mine.. thats the set!! alot of times you can just buy it in pieces too if you don't need everything at once!