Adapted from Yosemite National Park by Jeffery P. Schaffer

All the introduced animals together with their masters inadvertently brought in unwanted alien plants, insects, and associated diseases. Galen Clark, the Park's first guardian, noted that in the 30 years that passed after the Park was first created, the luxuriant native grasses and flowering plants of Yosemite Valley had decreased to only one-fourth of their original number. Part of this was due to grazing, part to other causes, and part to the new plant competition.

Overgrazing on the Valley floor resulted in trampled soil and bare spots, both inviting invasion by ponderosa pines and incense-cedars. Prohibition of fires insured the survival of young conifers which, as they matured, shaded out the once co-dominant black oaks. Finally, lowering the water table through blasting and ditching hastened this conifer invasion of the meadows. Throughout the 20th century the Valley's plant community has been largely a dense conifer forest with neatly defined, gardened meadows, not an open conifer-oak woodland.

Thanks to the Yosemite Fund (which you should join), the underfunded Park Service is now able to reverse some of the past damage. It has aided endangered peregrine falcons, great gray owls, and bighorn sheep, and has restored some meadows to more natural conditions. But how does one deal with the top predator, man?

The millions of annual visitors often has been perceived as the foremost threat to Yosemite's fauna and flora. However, the most pernicious threats usually go unseen and are beyond the control of the Park Service: man-induced global warming, increasing atmospheric pollution, upper-atmosphere ozone depletion, and habitat loss in middle and lower elevations of the Sierra Nevada and elsewhere in the Americas. The latter is of particular concern for Yosemite's birds, which in the fall typically migrate to lower elevations or to lower latitudes, such as to Central America. But everywhere the mounting human population is destroying habitat and the life it once held. For example, each person added to California ultimately causes enough habitat destruction to destroy, on average, up to one ton of animals, plants, and micro-organisms-something to ponder.