VTM 1937 Yosemite vegetation

National Park Service

This map of the vegetation of Yosemite National Park was developed in the 1930s as part of an effort to map the vegetation of California. It is often referred to as the "Weislander map", because A. E. Weislander was the United States Forest Service employee who oversaw mapping in the Sierra Nevada (and perhaps other portions of the state as well). The work was carried out by park staff under the direction of the park forester, Emil Ernst. The data development and field work were overseen by Yosemite NP Forester Emil Ernst from 1933-1935. The polygons were originally delineated on 1937 map drawn by Wieslander, et al (see below for reference publication.) This map was digitized by the USGS Biological Resources Division in the early 1990s (date currently unknown.) The field work occurred over multiple years, with different areas of the park mapped in different years. There are two historic hardcopy maps that indicate which areas were mapped in which years, but these two maps do not always agree. The general areas mapped between 1932 and 1936 are listed below: 1932: North side of Tuolumne Canyon below Hetch Hetchy 1933: Western boundary of park from South Entrance to Hetch Hetchy entrance, Yosemite Valley, White Wolf, Porcupine Flat, Illilouette Creek, Glacier Point Road area, Wawona, Lyell Canyon, Gaylor Lakes 1934: north rim of Yosemite Valley, Clark Range (northern portion), Little Yosemite Valley, Ostrander Lake area, upper Chilnualna Creak area 1935: South Fork Merced River above Buck Camp, Upper Merced watershed (above Little Yosemite Valley), Tenaya Canyon, watershed above Lake Eleanor, Tiltill Canyon, Stubblefield Canyon, Kerrick Canyon, Thompson Canyon, Slide Canyon, Matterhorn Canyon, Virginia Canyon, Young Lakes area 1936: Tuolumne Meadows, Glen Aulin, Tuolumne Canyon above Hetch Hetchy, Smith Peak It is not known precisely when the final map was compiled and completed, although it was likely done in the winter of 1936-1937. Hence, it is not possible to put a precise date on the map, a date that represents the vegetation of the park on a precise date (or even year). It is probably most useful to consider this map to be somewhat fluid in its birth date: the map represents the vegetation of the park that existed in the 1930s, notwithstanding year-to-year changes in vegetation due to fire, disease, forest succession, etc. This time period also represents the beginning of effective exclusion of fire throughout the park, although fuel loads at the time were probably light and frequent low-intensity fires were the norm. The exclusion of fire led to unnatural fuel accumulations and type conversions through various ecological mechanisms. Field work included primarily establishment of vegetation plots and field mapping (i.e. delineations). The vegetation plots collected data on dominant plant species (by no means a complete species list), distribution, leaf litter, soils, etc. The field maps were assembled and transferred to the final map. The final map is in "panels", presumably so that they could be folded and put into files or taken into the field. The panels were attached to linen and a protective coating applied to the map surface. The mapped area does not correspond exactly to the park's boundary. For instance, areas within the park near the east boundary were not mapped. These unmapped areas are generally defined by high mountains and may have been too difficult to map. Also, some areas outside the park were mapped by park staff. Minimum Mapping Unit (MMU): The concept of an MMU was apparently not used for this project; certainly, no documentation has been found. There are polygons as small as .1 acre, and polygons as large as many hundred acres, indicating that the "MMU" size varied depending on the accessibility of the area. Given the coarseness of the mapping in some of the less accessible areas of the park, a reasonable guess for MMU is 15-25 acres. Accuracy: The accuracy varies depending on t

VTM 1937 Yosemite vegetation

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