YOSEMITE Vegetational Changes in Yosemite Valley NPS Occasional Paper No. 5

In a soil survey, the soils of Yosemite Valley were characterized and mapped on 1962 aerial photographs (scale 1/12,000) according to techniques used in the California Soil-Vegetation Survey (Zinke 1962). Profile characteristics served to delineate soils with their classification based on mode of origin and topographic position. Field mapping extended from Artist Creek below Pohono Bridge to Vernal Falls along the Merced River and to Snow Creek in Tenaya Canyon. Vertically, mapping included the talus slopes. Types were mapped to a minimum area of 0.4 ha (1 acre). After field mapping, the information was transferred to the U. S. Geological Survey, Yosemite Valley Quadrangle, scale 1/24,000, 1961 edition base map.

The mapped soil units, 346 in the forest and 48 in meadows, constitute the basic sampling divisions for analyzing the vegetation reported herein. However, the elimination of small soil units and the addition of a few units from widespread soil types resulted in 280 being sampled.

A singular circular vegetational plot 15 m (50 ft) in diameter was located near the middle of each mapped forest type. The investigator tallied woody species in height classes as less than 0.3 m (1 ft), 0.3-1.8 m (1-5 ft), 1.8-6 m (5-20 ft), 6-15 m (20-50 ft) >15 m immature, and >15 m mature. Within each height class, the number of plants per plot was recorded in classes of 1-5, 6-25, 26-100, and >100. Ocular estimates to the nearest 5% characterized total crown cover above 1.4 m (4.5 ft), herbaceous cover below 1.4 m, and litter cover. Herbaceous species were listed for each plot. Frequency of browsing on each woody species was estimated on each plot.

The point system with a frame that held 10 pins was used for sampling the meadows. Groups of 10 points were read on a paced grid for a total of 400 to 800 points within each meadow soil-vegetation type.