Chad- As others have stated there are alot of legal issues involved. Are you granting an easement or is this hostile (emminent domain)? If your owners are granting an easement there will be a settlement (lump sum) which sounds like what you are involved with. You might consider hiring a consulting arborist or a professional plant appraiser. Experts talk about a "Cost Approach" where you simply repair damages to trees and/or replace the plants removed if they are relatively small. For larger plants there is a formula which factors the size, species, condition, and location. They normally calculate a price per inch, for instance if a 4" Oak costs $400 it is $100/inch. Then a 12" tree is worth $1200, then a species factor, condition, and location. I would give anything on a golf course a 100% value. This ISA link may help
http://www.treesaregood.com/treecare/tree_values.aspx.
There are "Income Approaches" which is green fees, etc. and "Market Approaches" which involve real estate appraisers. Good luck. Kenneth Ingram, UMD.