| OCR Text |
Show THE LIFE ZONE MAP CHAPTER xi METHODS USED It is realized that the life zone concept is open to serious criticism when used for intensive studies of small areas, and that when used for any purpose it may be open to charges of vagueness. Although the present treatment cannot hope to escape altogether such charges, an effort has been made to designate the limits of the zones as definitely as possible. It was only after weighing all the factors involved that the decision was made to describe the Colorado River Basin in terms of life zones rather than by plant associations comparable to those used by most ecologists today. The deciding factor was that of simplicity for the benefit of the average nonscien- tific reader. It was believed that loss of critical definition, resulting from the use of these more generalized zones, would be more than compensated for, in semipopular treatise, by the reduction in number of classifications. The life zone map of the Colorado River Basin is like nearly all maps of large areas that have ever been made, in that no matter how great has been the expenditure of care and energy to insure its accuracy, someone more familiar with local areas can discover errors of various degrees of importance. In the case of the present map, much less time was available for its preparation than originally had been anticipated, owing to circumstances beyond the control of the Colorado River Survey project. In fact, the life zone study never could have been completed if it had not been for the air surveys, which made possible a fairly comprehensive coverage of the basin within a period of only 9 months. Even so, the final product would have been much less accurate had it not been for the generous help, elsewhere acknowledged in full, of many persons having an extensive technical knowledge of various parts of the basin. As a first step, all available botanical, zoological, and ecological publications were consulted in order to establish the average elevation boundaries of all of the life zones in the various parts of the basin. By no means all of these publications were specifically concerned with life zones, but since the major plant indicators and association equivalents of the zones have long been recognized, any information on the distribution and elevation of these indicators in various parts of the basin could be translated fairly easily into terms of life zone boundaries. These preliminary data were summarized as follows: Life Zones- Lower Limits [ Elevations indicated in feet above sea level] State Slopes Upper Sonoran Transition Boreal Authority New Mexico ( all) E. and West N- facing S- facing N- facing S- facing 4,700 4,500 5,000 4,000 5,000 below 5,000 7,500 6,800 8,000 6,000 7,000 7,000 9,000 8,500 9,500 7,500 9,000 N. 7,500 S. 9,000 Bailey ( 1913) Arizona ( northern) Bailey1 average elevations Shreve ( 1926) l Bailey, Vernon, Mammals of the Grand Canyon National Park, U. S. Department of Interior, MS. 220 |
