What is the concept a logger is using when he removes a particular fraction of trees on a job site in order to allow a certain amount of light to penetrate the forest floor for the younger trees?

Answer: Maximum sustainable yield.

Explanation:

The logger is applying the principle of maximum sustainable yield to increase the forest trees yield.

Maximum sustainable yield in forestry is a method of harvesting that enables more productivity in the forest, where older trees are chop down, so that younger ones can access the much needed resources like sunlight and land nutrients.