Douglas Fir management

Asked January 27, 2020, 8:25 PM EST

I’m planning to do a commercial thin on my Douglas Fir stand when in reaches 25 years old. On average what spacing should I plan to leaving the remaining standing trees? Thanks a bunch!

Lane County Oregon

1 Response

The amount of space a tree needs is dependent on its size. Larger trees need more space than small trees. Therefore, without knowing the current size of your trees, it is difficult for me to tell you how far apart they should be. That being said i have a few resources for you. The first is a great publication called competition and density in woodland stands which can be downloaded for free here: https://catalog.extension.oregonstate.edu/em9206. With this publication you will learn to use the relative density scale and a stand density table specific to your tree species to determine the best time to thin your trees and to what density in order to achieve your desired results.

If you are looking for a more quick and dirty approach then you an use the D+ rule.The D + Rule states that the amount of adequate space between your trees to ensure growth and general health as a function of soil quality and sunlight. Spacing is equal to “D”, the current diameter of the trees at breast height (4.5 ft off the ground) of the trees, and “+” the additional space needed. For Douglas fir in our area I recommend the D+6 rule. For example, 12” diameter trees should be thinned to an 18 foot spacing (12 + 6). This is a general rule and specific characteristics of your stand may warrant lesser or greater spacing.

If you'd like to discuss this further, or get a more specific distance for your soil and trees feel free to reach out to me directly Lauren Grand. Or write me back answering these questions.

What is the current Trees per acre of the stand you are planning to thin?
What is the current Diameter of the trees at breast height (DBH , 4.5 ft off the ground)?
If you don't know these numbers here is a publication to help you. https://catalog.extension.oregonstate.edu/pnw630