When I interned at Muir Woods, heli-tours flew over the park, creating such loud noise that I and other rangers were forced to stop our talks until the helicopters passed. Silence, argued the head ranger, was an integral part of the redwood forest. Few animals live in redwood forests—-silent slugs, silent deer, silent mountain lions, silent northern spotted owls. Even wind causes little noise there, as redwoods tend to grow in sheltered areas since they are so tall and their roots so shallow.
Yosemite and Muir Woods represent two protected natural areas—-what aspects of these natural areas is the Park Service meant to protect?
The National Park Service preserves unimpaired the natural and cultural resources and values of the national park system for the enjoyment, education, and inspiration of this and future generations.
We emphasize the visual component of these resources, and neglect the aural (and functional, but that's another story) properties of wilderness. Why? Our physical capabilities that make us visually reliant?
Man has impinged upon most other ecosystems and natural areas. To what extent should we condone man's spread and dominance by saying that man is simply an extremely successful species? To what extent does man's success rely on modifying the environment to the detriment of other species, and how does that compare to other invasive species? To what extent should man, as just another competitor for limited resources, respect existing ecosystems? How can we balance our own success with the importance of biodiversity?
National Parks are America's first attempt to preserve patches of ecosystems intact from man's influence. If we believe these places are important, both inherently and as a baseline to see how the world would be without us, we should protect them completely. In this instance, we must ask: is the preservation of natural soundscapes important enough to divert economy-influencing air traffic? If you think soundscapes seem important, read about the One Square Inch Project, which aims to protect one square inch of land in the U.S. from noise pollution.
If you're more visually oriented, perhaps consider participating in Lights Out San Francisco on Oct 20 or your city's equivalent, which you can find through the Dark Sky Association, or in a world-wide Star Count to index light pollution.