Study of crown shapes of Douglas fir, western hemlock, and western red cedar as an aid in the identification of these species on aerial photographs

The photo-interpreter has a difficult task when he is asked to identify the images of tree species recorded on aerial photographs. When a tree is examined on an aerial photo for such a purpose, the difficulty becomes more and more evident as it is realized that the different species can not always he identified by eyesight, even on large-scale photographs, but must be viewed stereoscopically, and the variations in appearance within the same species, even growing under the same conditions, are very great. In comparison with identification on the ground, the interpreter must take an entirely new approach in the determination of various species from aerial photographs. This approach involves training the eyes to recognize plants appearing with various hues and grey tones on black and white photographs, at much smaller scale than usual in ground studies, in most cases from above or half-oblique view of the tree, which is strange to the inexperienced interpreter. Most of the trees appear on aerial photographs in vertical or oblique views, when the branching habit and the crown shape of a tree are easily visible. For this purpose it is desirable to know the characteristic branching habit and typical crown shapes of trees in order to use these factors in species identification. This leads up to the problem that will be presented in this thesis. Factors which influence the ground characteristics of three major tree species in British Columbia are examined and analyzed. Various crown forms, with which Douglas fir, western hemlock and western red cedar occur in the vicinity of Haney and Vancouver, are described. The basic pictorial elements, with which these species appear and enable us to recognize them on aerial photographs, are analyzed. Influence of different films and filters on the appearance of species on air photos are also discussed. The thesis presents an analysis of identifications of species made by several interpreters. Requirements for photo-interpretation are also discussed. Finally, a dichotomous key is presented, which is constructed for Douglas fir, western hemlock and western red cedar, taking into account their appearance at various ages and locations.Forestry, Faculty ofGraduat