Vegetational Changes in Yosemite Valley
NPS Occasional Paper No. 5
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This study and others, coupled with long experience in Yosemite Valley, show that the vegetation must be managed continually to preserve views and safety. The first three of the following suggestions are the most important.

1. Large areas of relatively open forest should be developed and maintained for their beauty and access to visitors. Considerable tree removal and prevention of forest regeneration will be needed. The Indians did this with fire and by pulling young trees. The modern manager should use the same tools selectively. For example, Pinus ponderosa and Quercus kelloggii may be encouraged in one place, but forests dominated by other species should be developed on different sites. Vegetational management within the forest types is needed to make them safe from catastrophic fire and to decrease the likelihood of property damage and human injury from falling materials. Management should follow development of a vegetational management plan for the valley.

2. Large ground accumulations of woody debris and the continuous vertical canopy created by trees of many heights produce an excessive wildfire hazard (Fig. 21). These fuel conditions could cause extensive conflagrations during dry, windy weather. Understory fuels along roads and in irregular strips through the forest should be reduced by removing dead limbs from large trees, eliminating small overtopped trees, and prescribed burning of the accumulated debris during safe weather conditions. Burning was a natural process in the pristine Yosemite Valley. The ultimate objective should be restoration of open forest conditions by reducing large bodies of fuel in nearly all the forests on and below the lower talus slopes.

Fig. 21. Fire hazards have become extreme in parts of Yosemite Valley due to the accumulation of fine fuels from ground level into the tree canopy.

3. The meadows must be maintained and preferably enlarged to attain a maximum variety of views of mountains, cliffs, and waterfalls. To achieve this, techniques such as pulling and cutting young trees, cutting large trees, and prescribed burning can be used. Any debris should be spread thinly or burned during periods when fire danger is minimal. Prescribed burning should be used on meadow areas where tree regeneration is abundant. Vistas cut through forests should be wide and irregular to give the appearance of natural openings. The forest should not hide the views and consequently reduce the value of Yosemite Valley as a recreational site.

4. Road maintenance, building, and most other development leave bare soil which should be seeded to grasses such as Poa pratensis, Festuca rubra, Bromus inermis (smooth brome), and Lolium spp. (rye grass) to attain a quick cover that will reduce erosion. These species spread throughout the valley in the 1800s as a result of forage grown to feed livestock. They have become a part of the natural meadow vegetation and nothing about them gives the appearance of intrusion into the valley, nor can they be removed by any known means. These species should be considered native species. Seed is available at low cost and there is no danger that they will displace the native vegetation beyond that which occurred several decades ago. Flowers might be planted along new roads but they will disappear as the grasses invade. Heavy grassland litter and thick growth generally reduce plants with highly conspicuous flowers. The alternative to seeding is to allow bare soil to revegetate naturally because seeds of the native species are not available. When development or construction leaves bare soil, it should be seeded without waiting for natural plant succession to take place.

5. Paving of additional trails on the meadows and lower talus slopes will reduce erosion and serve as fire lines. Hikers tend to use paved trails, which saves the soil from trampling and erosion.

6. Removal of large weeds, such as thistles, and trees hazardous to visitors should continue on a planned basis open to public view.

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Last Updated: 20-Nov-2007