Creating a tree block at the right size for Replace Tree Symbol Function
For your trees, you need to make sure that the tree blocks that you are using are at a 1m radius
Draw a circle at 1m radius and make sure the tree is the same size as the circle and resave the block showing the correct sizes.
Once you have the tree created at the riht size you can then go to the Tree Block Definition and set the right block for the right parameters for the trees.
After setting these items you just need to run the replace Symbols function and all your trees will be replaced with the right tree block at the right radius size as measured in the field. e.g. 201 .2 5 8 or TR .25 6 etc.