HYDROLOGIC REGIME AND HERBIVORY STABILIZE AN ALTERNATIVE STATE IN YELLOWSTONE NATIONAL PARK.

The article focuses in determining the relative influence of hydrologic regimes, as controlled by climate variation, beaver damming, and landscape changes, on the process of Yellowstone's northern range. The study was made with four streams on the northern range of Yellowstone National Park, USA. The four streams were selected because they have relatively large willow populations, have a riparian zone where groundwater is supported by streamflows, and lack significant hillslope groundwater inflows. Willow establishment data were compared to 20th century streamflow and precipitation data in detecting climatic influences on the timing of establishment. The reduced frequency of willow establishment during the 20th century is likely both a direct and indirect effect of elk browsing.