Section 47. As used in sections forty-seven to fifty, inclusive, the following words shall have the following meanings, unless the context clearly requires otherwise:—

”Forestry”, the science, the art and the practice of conserving and managing for human benefit the natural resources, including trees, other plants, animals, soil and water, that occur on and in association with forest lands.

”Practice of forestry”, any professional services requiring the application of forestry principles and techniques. Such services shall include, but not be limited to, forest inventory, forest management planning, timber appraisal, the responsibility for the direction and supervision of silvicultural activities, use and protection of forested areas, and the evaluation of the economic and biological consequences of forest management activities.