One Hundred Hikes in Yosemite

The Living Yosemite — Physiographic Influences

The topography indirectly affects the distribution of plants and animals. As we have seen, a change in elevation means a change in temperature and precipitation, and irregular topography can create uneven distribution of snow. Well-named Snow Flat is at about the same elevation as Tuolumne Meadows, yet because it lies south of Mt. Hoffmann, it receives about twice as much snow as Tuolumne Meadows, which lies just north of the Cathedral Range. This range creates a "rain shadow" on its north side, so less precipitation falls over the meadows. The Sierra crest creates an even greater rain shadow, which explains why Mono Lake, in the table, has such a low precipitation—about 30% of the maximum figure.

Topography also affects vegetation in other ways. A north-facing slope, because it receives less sunlight than a south-facing slope, is cooler, so evaporation and transpiration on it are less. Consequently, it can support a denser stand of vegetation. This denser stand produces more litter, which results in more humus, so ground water is retained better. In one soil survey conducted by the author, about 60 percent of a soil's weight on a north-facing slope was due to water, whereas on a nearby south-facing slope, only about 5 percent was due to water. This was an extreme case, but, nevertheless, it helps one to visualize why north-facing slopes tend to be heavily forested while south-facing ones tend to be more open and sometimes brushy. At mid-elevations we see red and white firs on the shady slopes and Jeffrey pines and huckleberry oaks on the sunny ones.

Published: 29 Apr 2002 | Last Updated: 15 Sep 2010
Details mentioned in this article were accurate at the time of publication


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