Not seeing the land it is almost impossible to give any kind of approximate value to your timber. Call your local county forester and ask what kind of help they can give. There's different regulations by the states as to what they will let their foresters actually do. While a 40 acre tract is smaller than most like to mess with, having good access roads, good terrain to work on and what kind of timber you have will determine what you can get for the timber. If the county forester can not help give a cruise value of the timber you will probably need to hire a consultant forester to help with your timber sale. Have a clear understanding with the consultant as to the percentage rate of payment and specifically what you will get for their services.