Tuesday, June 19, 2007 - 3:15 PM Ponderosa Pines (Boise Centre on the Grove) 406
The Influence of Disturbance Events and Rehabilitation on Sagebrush Steppe Ecosystems
Stuart W. Murray, High Desert Ecology, Boise, ID
Disturbance events such as grazing and wildfire are common events in sagebrush steppe ecosystems in the intermountain west. Several models have been developed to explain changes in the composition of the vegetation as a result of these disturbances. The state and transition model is the currently accepted model and incorporates non-equilibrium theory to evaluate the conditions of a community based on species composition. However, the descriptions of the states are often qualitative and therefore difficult to use in determining the state of a community based on sampling data. To address this issue, quantitative canopy coverage values for shrubs, perennial forbs, grasses and annuals were estimated for each state in the state and transition model using prior studies from the literature. These values were then compared to sampled vegetation data collected from sagebrush steppe communities that had experienced recent wildfires. The relative canopy coverage and the state of these communities differed by aspect, burn history and rehabilitation efforts. North-facing slopes experiencing moderate intensity fires can recover without rehabilitation. Disturbance caused by re-seeding or replanting activities on north-facing slopes may provide conditions for the invasion by non-native annuals and can therefore be counterproductive. South-facing slopes have warmer and drier conditions and require rehabilitation efforts to avoid monocultures of invasive annuals following wildfire. Intensive rehabilitation efforts on south-facing slopes appear to facilitate the transition of plant communities to a more pristine state.