233. Formation and vegetation maps are detailed maps of a single formation or a series of them, showing the formational limits, and when the scale is not too small, the ecotones of zones and consocies. In the cases where the topography is level, as sometimes happens in mapping single formations, the chain and pedometer must be used to ascertain the size of the different areas. Indeed in all mapping of vegetation, the methods of surveying are directly applicable. Over large areas, however, it is not necessary that limits be drawn with mathematical accuracy, and for the purposes of the ecologist, the plane table and camera are satisfactory substitutes for the surveyor’s transit, at least in the present aspect of the subject. When the formation or group of formations is commanded by an elevation of some height, the latter is used as a base. A plane table is established upon it and the topographical and vegetational features are recorded in the usual way. This map is usually supplemented by a series of views from the same base. Indeed it has come to be recognized that a complete series of photographs of this kind give a more valuable record than the plane table, and that the construction of an accurate map from them is an easy matter. Since the camera saves much time and energy also, it is used almost exclusively to furnish the data for map making. In hilly, and especially in mountainous regions, the photographic method is indispensable. Its application is extremely simple. A central hill or mountain is selected, and from it a series of views is taken so that the edge of one exactly meets the edge of the other. This is an extremely important matter, and demands much nicety of judgment. The camera is kept in the same spot, and after each exposure it is turned as the operator looks through it until a landmark at one edge just passes from view at the other. As soon as the new position is determined, the tripod screw is turned to hold the box firmly in position. In case of a slight jar, the exact position should again be obtained. If the series is accurately made, the resulting prints will give a complete panoramic view of the region, without overlap or omission. For this purpose, a 6½ × 8½ camera is desirable, since the topographic and vegetational features are larger and stand out more distinctly. A large camera requires fewer changes of position, and hence saves time and reduces the chance of error. A 4 × 5 camera serves the purpose sufficiently well, though it requires a little more care in operation on account of the greater number of exposures necessary. This may be avoided in some degree by the use of a wide-angle lens if the depth of the area is not too great. Whatever camera may be used, a telephoto lens is a very desirable adjunct, since it enables one to choose between three different sizes of the view without changing the position of the camera. To avoid possible confusion, the exposures are always made from right to left, and the plates are used in the numerical order of their holders. For the same reason the landmarks are described and numbered in their proper order. The prints obtained are mounted on a card in sequence. The view map may be preserved in this form, or it may be reduced or enlarged by making a copy to the size desired. Outline maps of topography may be traced from the resulting negative, and the formations filled in by means of the proper colors. The most satisfactory method, however, is to have the original views or the copy printed “light” and to color the formations just as they appear there, with all the wealth of topographic and vegetational detail. If a detailed topographic map alone is desired, this is traced directly from the large copy.
234. Continental maps. A method of determining the general outlines of regions, provinces, and vegetational zones as a preliminary to their detailed study has been used successfully for several years.[[22]] This is based upon provincial and continental maps on which are traced the geographical areas of the species of genera typical of the various formations. Detail topographic maps of the prairie province and the North American continent have been used for this purpose. A number of the facies of extensive and representative formations of the different portions of the continent are selected and grouped according to genera. One map is devoted to each genus, unless the number of species is large. In this case a number of maps are used, since the limits are apt to become confused. The range of each species is determined from all the reliable sources, and a corresponding line is drawn upon the map to delimit its geographical area. The limits of the area of each species are drawn in a different color, and the name of the species printed in the same color in the legend. Although this work has as yet been done only for the trees of North America, and for the grasses and principal species of the prairie province, it promises to constitute a final method for the limitation of vegetational divisions. It is clear that if the original data concerning ranges are accurate, the increasing study of formations will do little more than rectify the detailed course of the limiting line, since in most cases facies and formations coincide in distribution. The limiting line or ecotone of a zone or province is a composite obtained from the limits of certain representative facies and principal species, and checked by the limits of species typical of the contiguous vegetations. Thus, the boreal-subalpine zone is clearly outlined by combining the limits of Populus tremuloides, Larix americana, Pinus banksiana, Abies balsamea, Picea mariana, Picea canadensis, and Betula papyracea, and checking the results by the areal limits of the hardwoods and grasses to the southward.
PHOTOGRAPHY
235. The camera is an indispensable instrument for the ecologist. Although it has too often been employed to give an air of thoroughness to work of no ecological value, it is as important for recording the structure of vegetation as the automatic instrument is for the study of the habitat. No ecologist is equipped for systematic field investigation until he is provided with a good camera and has become skilful in its use. For this reason, it is felt that a few hints concerning photographic methods and their application in ecology may not be out of place. No written advice can take the place of experience, but certain elementary suggestions and cautions will greatly shorten the apprenticeship of one who does not have the good fortune to be taught by a professional photographer. To the student of ecology, the camera is not a toy. It must be understood and operated with as much thoroughness as any other instrument, and when this is done, the results will be equally certain and desirable.
Fig. 56. 4 × 5 long focus “Korona” camera (series V).
Fig. 57. 5 × 7 long focus “Premo” camera.
236. The camera and its accessories. Although two cameras are desirable whenever it is possible to obtain them, a single one will meet all the requirements of field work. This should be 4 × 5 inches in size, since it is much more convenient and will do all the work that a larger camera can. In the comparatively few cases in which larger views are needed, the 4 × 5 negatives can be readily enlarged. The smaller instrument is less expensive in operation because of the cheapness of the plates, and it gives a negative of the proper size for lantern slides and for reproduction. A 6½ × 8½ camera is valuable in special cases, such as making a series of photographs for maps. In the writer’s own experience, the 6½ × 8½ camera, although used exclusively at first, has been almost completely supplanted by the 4 × 5. The best field camera is of the folding type with a good stout box. It must be what is known technically as a long focus instrument, which enables small objects to be taken natural size and permits the use of a telephoto lens. It should be provided with a swing and also a reversible back by which the position of the plates can be changed instantly. The lens must be of the telephoto pattern, which makes it possible to use the front or back lens either alone or in combination. The chief advantage of this is that the image, when distant, may be made of three different sizes without changing the position of the camera. Generally speaking, the high-priced rapid lenses are the best, since it is exceptional to get the desired length of exposure in vegetation, on account of the ease with which the plants move in the wind. Before buying such a lens it is desirable to test its rapidity and depth of focus, since it is not necessarily better than some of the lenses furnished with good cameras. The lens should be provided with an iris diaphragm capable of being stopped down to 128 or 256. The shutters furnished with the ordinary lenses are satisfactory, since “snap-shots,” i. e., instantaneous exposures, are practically never possible for plants. The automatic shutter of the “Premo” camera is an especially convenient form. All shutters should be carefully tested before using to determine the exact time value of the exposures indicated. It is not uncommon for the exposure at 1 second, or at other points, to have a value quite different from the one indicated. When this is the case, it is evident that it can not be known too soon. The camera should have at least a half-dozen double plate-holders. These are numbered consecutively so that the figure uppermost when the holder is in the camera will indicate the number of the plate exposed. A carrying case is desirable on a long trip when all the plate-holders must be taken, but ordinarily it is a disadvantage, since the camera box will carry two or three holders. The camera cloth should be as small and light as possible, and at the same time opaque. The most satisfactory one for the field is the rubber cloth. The tripod should be a happy combination of lightness and stability, a condition more nearly reached by the aluminum tripod than by any other. It should have not less than three joints in order to facilitate the use of the long focus upon objects near the ground.
