Step 1: Understanding the Question:
This question tests knowledge of forest mensuration and crown competition.
Step 2: Detailed Explanation:
The crown competition factor (CCF) is the ratio of the average crown area available to a tree to the maximum crown area it would have had without competition.
It is used to assess competition in a stand.
Crown density (A): Not a standard term.
Crown point (C): Not a standard term.
Crown area index (D): Not a standard term.
Thus, the correct answer is crown competition factor.
Step 3: Final Answer:
Thus, the ratio is called crown competition factor, which corresponds to option (B).
[0.5cm]