Answer:
Inductive Reasoning
Explanation:
Inductive reasoning is one of the two approaches to draw a conclusion from the given observations. Inductive reasoning includes making observations and then drawing "a general conclusion" about the observed phenomenon.
Inductive reasoning in biology makes observations about specific processes while the conclusion is applied to a broader category of the organisms.
In the given example, the process of leaf fall during autumn is observed in walnut and Ginkgo trees in response to the reduced day length while the conclusion is applied to "many tree species" irrespective of their phylogeny or any other criteria. Here, it represents inductive reasoning.