Thanks for your question. To find the monetary value of your trees, you need to know the following: the tree species, how many of each species is out on the property, and the number of merchantable trees per species. If you have a forest stewardship plan attached to your property, there should be information on (at least) the first two points I listed. You can then calculate the potential value of the trees based on how many there are/their species, and their potential market prices. Maryland does not have records of timber prices, but PA and VA both do - you can access these prices by pulling up quarterly reports (https://extension.psu.edu/forests-and-wildlife/forestry-business-and-economics/timber-market-report), (https://timberupdate.com/timber-prices/virginia-prices/)

An easier, rough-estimate way to do this is to harvest and sell your trees and keep track of the volume that you sell and the rates that are paid. You can ask the buyer what their rates were 10 years ago and compare the differences - keep in mind that trees increase in volume over time, so even if rates were higher 10 years ago, your trees were likely smaller. Also note the impacts of inflation over time.

If you are concerned with taxes, check out these resources: https://www.timbertax.org/, https://www.fs.usda.gov/spf/coop/library/Forest%20_Tax_%20Guide.pdf, https://www.timbertax.org/2012QuickGuide.pdf (the last link is the most helpful, in my opinion). Penn State hosts a short course on timber taxes, in case you need the details of a several week class.

Long story short - call your county DNR forester to see if they have inventoried your property and if they can discuss timber values on your property. The, check out the linked taxes resources above.