XVI International Botanical Congess

Fire is the dominant disturbance in the coniferous woodlands that characterize the ecotones between montane forests and steppe vegetation in Northern Patagonia, Argentina and in the Colorado Front Range, USA. In both areas, relatively high fire frequencies prior to the late 1800s were the result of both lightning ignitions and fires set by Native American hunters. Fire exclusion during the present century has resulted in dramatic tree invasions of former grassland sites and has significantly altered stand susceptibility to insect outbreak and crown fires. Years of widespread fire in both regions are closely linked to variations in the El Nino-Southern Oscillation at both inter- annual and multi-decadal time scales.