help with tree trunk (horizontal) slices

I am trying to provide a horizontal slice of a tree trunk for a friends project. She will use this 14 inch diameter slice (from a tree trunk) to display a cake on. The slice is about 3 inches thick. As these slices sit in my garage (curing) they always split. I don't know what kind of tree they are from. Do I need to use a specific type of tree? I live in Dallas Texas and would sure appreciate some advice. Sadly, i can't attach a photo of the slices i've been working with but hopefully, you will understand from my explanation.
Thanks, [email protected]