Current Human Impacts on the Ecosystem

Yosemite National Park receives about 3.5 million visitors a year.  Yosemite supports over 400 species of animals and plants.  (Hutter, 2011) Humans outnumber animals and cause serious threats to Yosemite's wildlife and ecosystems.  Although the park provides high-quality habitats, approximately 40 species have a special status under California endangered species legislation.  ("Yosemite National Park", 2011) Human impacts on the ecosystem include loss of a natural fire regime, air pollution, habitat fragmentation, and climate.  On a more specific and local basis, factors such as the availability of human food and occurrence of road kill can negatively affect wildlife species.  Three species- the grizzly bear, the California red-legged frog, and foothill yellow-legged frog- are believed to be destroyed in the park within recent history. 


The introduction of exotic or non-native species that cause forest pests is also a problem.  Forest pests result when non-native insects and diseases are introduced into an ecosystem and cause environmental damage.  When humans bring firewood from outside the valley into campsites, non-native animal, plant, and disease species can get into the ecosystem.  Agents such as Sudden Oak Death, light brown apple moth, Asian long horned beetle, and Formosan termite are four species scientists are particularly worried about.  Forest pest problems have grown throughout the past 150 years. Non-native insects and diseases not only inflict harm on the species they attack, but also on associated plants and animals in their food chain.  The large number of species affected may become extinct simply because a camper brings in firewood from home.  


Areas of concentrated human use in Yosemite affect wildlife by removing, fragmenting, and degrading habitat, which affects the diversity and abundance of some species in those areas.  These effects are limited to relatively small areas of the park, but a history of 80 years of fire suppression in Yosemite has really affected wildlife habitat over a larger span of area in the park.  Fire is a natural, necessary occurrence because it maintains a healthy mixed habitat in vegetation that provides ecological niches for wildlife.