Greetings, I am sending this along to someone who works in the geographic area of Douglas Fir.  Roots will not typically grow long after a tree is harvested however due to the need for photosynthetic resources.  That being said, roots can obtain some of their necessary sugar requirements from the soil.  So it is complicated.

No, Douglas fir (Pseudotsuga menziesii) roots will not continue to grow after the tree is felled. Once a tree is cut down, the roots no longer receive the necessary nutrients and energy from photosynthesis, which occurs in the leaves. Without this essential supply of carbohydrates, the roots cannot sustain growth.

Key Points:

1. Photosynthesis Dependency:

   
   

   • Trees depend on photosynthesis to produce carbohydrates, which are essential for root growth and maintenance. Once a tree is felled and the leaves are no longer present, this process stops, halting the supply of energy to the roots.
2. Nutrient Transport:

   
   

   • The vascular system of the tree, which includes the xylem and phloem, is disrupted when the tree is cut down. This system is responsible for transporting water, nutrients, and sugars between the roots and the canopy. Once the connection is severed, nutrient transport ceases, further preventing root growth.
3. Root Lifespan:

   
   

   • While some tree species can sprout new growth from the stump or roots after being cut, Douglas fir is not typically one of these species. Its root system is not adapted to sustain itself or produce new shoots after the tree is felled.
4. Decay Process:

   
   

   • After a Douglas fir tree is felled, the roots will eventually die and decompose. This process can take several years, during which time the roots will break down and return nutrients to the soil.

Exceptions and Related Phenomena:

• Coppicing and Root Suckering: Some tree species can regrow from stumps (coppicing) or produce new shoots from roots (root suckering). However, Douglas fir generally does not exhibit these behaviors.
• Mycorrhizal Networks: Although the roots themselves will not grow, the mycorrhizal fungi associated with the roots may continue to exist in the soil for some time, potentially benefiting other plants and trees in the vicinity.

In summary, once a Douglas fir tree is felled, its roots will cease to grow due to the loss of photosynthesis and nutrient transport, leading to their eventual decay and decomposition.