This paper presents a study on the works of ancient writers that deal with trees, forests and the use of forest before the time of actual forest sciences. The work describes the development of knowledge pertaining to the forest and trees and the progress made on utilizing them. This first part of a series of two articles is primarily concerned with biological information in ancient times. The article first describes the most important sources of information and concentrates then on the information on the structure of trees, on the vital functions of trees, on the factors affecting the growth of trees and tree species.