Penn State University does a great job of producing webinars on woodland management.  This one should help in assessing the value of your timber.

Making the Grade is a presentation which shows the relationship between lumber grades, log grades and tree grades with respect to estimating the quality and quantity of lumber which one may expect to recover from the board, log, or tree, respectively. The presentation covers basic information and does not require an in depth understanding of Forestry or Wood Products Manufacturing to understand the subject material. It is intended for small woodlot owners, farm woodlot owners, portable sawmill owners, public and municipal forest land managers, hunting camp wood land owners and other interested parties to help them better understand the Forest resource they own and/or work with.

This recorded webinar can be accessed HERE.