Answer: I'm sorry about your tree!
This type of appraisal is really difficult. Basically you have to look at how much the loss of that particular tree reduces the value of your property, and also how it could be replaced or what would have to be done to restore that landscaping value. It is not really practical to replant a matching 30 foot tall tree (it most likely would not survive even if you could find someone who would try it for you), so it is not clearcut as to how to go about that.
I think you will probably want a consulting arborist (make sure they are professionally trained and certified and licensed and have experience in residential trees) and also a qualified and licensed real estate appraiser and also maybe your federal income tax preparer.
Here are two publications you may find helpful in understanding how to go about determining the tree's value. You may need to cut and paste the complete url into your browser to make it work correctly.
Landscape Tree Appraisal
Landscape Tree Appraisal for Claiming Tax Deductions
I hope this helps!
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