(jane joyce) changes in the water cycle are not the only result of a warming climate. (dr.agre) our tree lines are changing rapidly as well. many of the broad fields of alpine wildflowers are gradually being encroached upon by these trees. as you have these wetter and warmer temperatures you grow more forests, so our potential for forest fires increases. (jane joyce) from warming temperatures, to changes in the water cycle and plant growth, climate change affects the dynamics of the entire mountain ecosystem.

[drum & synth fanfare] (jane joyce) yellowstone national park is one of the best places in the modern world to observe the complex processes that shape natural ecosystems, and how one change can trigger many unexpected ones. in the early 1900's, because yellowstone's wolves were considered a menace by humans; the animals were deliberately killed to reduce their population. once the wolves, yellowstone's top predator, had been eliminated, the elk population surged and devoured sprouting aspen and cottonwood trees in yellowstone's northern range. in 1995, in an effort to control the elk population "naturally," gray wolves were reintroduced from canada into yellowstone national park. as expected, the wolves preyed on the elk herds, by now, cutting their numbers in half. but unexpected changes occurred as well. as a consequence, aspen and cottonwood trees are again growing tall. their regrowth has allowed the beaver population to increase. small beaver dams have reappeared, and the ponds behind them allow trout to flourish. more succulent plants survive in the ponds' wetlands, providing c