Water Resources Research Act Program

Principal Investigators: Clayton Marlow

Abstract: Woody plant encroachment into grassland ecosystems has been reported on a global scale (Huxman, T.E., Wilcox, B.P. 2005). The rate of encroachment is most pronounced in adjoining riparian areas where high levels of wildlife and livestock use leave ecosystems vulnerable to invasion by woody species like Douglas fir (Pseudotsuga menziesii), Rocky Mountain juniper (Juniperous scopulorum) and Russian olive (Elaeagnus angustifolia) (Auken, Van, O.W. 2000).Comparing past vegetative community structure with current vegetative community status, makes it apparent that we must reassess current management strategies due to the decrease in hydrologic activity within watersheds. Consequently, future ecological studies must take into account the health of the entire ecosystem, not just the terrestrial system, due to changes in climate, grazing pressures, and hydrologic conditions. An example of this redirection in thinking is an investigation of Quaking aspen (Populus tremuloides) decline throughout the Western U.S. Historically, aspen was found in large expanses throughout the Rocky Mountain and Great Basin landscape. Stands were kept free of encroaching conifers by fires which occurred on a regular 3 to 15 year cycle. Fire suppression programs have been aggressively implemented since the early 20th century so disturbance by fire is no longer a component of riparian vegetative communities and shade tolerant conifers are invading former aspen stands. Aspen replacement by conifers could lead to negative changes in hydrologic activity within adjacent riparian areas (Ansley, J.R 2000).