Ecological resistance to invasion and resilience to disturbance – importance for restoring and managing Great Basin ecosystems

Background/Question/Methods Applied scientists are increasingly using the concepts of ecological resistance and resilience to develop approaches for managing and restoring ecosystems.  In the Great Basin of the western United States, invasion of non-native annual grasses into salt desert and low- to mid elevation sagebrush ecosystems is increasing fine fuels and resulting in larger and more frequent fires. Expansion and infilling of pinyon and juniper trees into mid- to upper elevation sagebrush ecosystems is resulting in higher fuel loads and increasing the risk of more frequent, larger and higher severity fires.  Both of these processes are causing the loss of native shrubland species and leading to widespread ecological degradation.  Consequences include increased risk to human life and property, high fire management costs, and loss of economic resources.  I discuss general patterns of resistance and resilience in Great Basin ecosystems based on research on factors affecting resistant to non-native annual grasses and resilience of shrubland ecosystems to fire.  I then suggest approaches for using this information to prioritize vegetation management activities on the landscape and to determine appropriate treatments for restoring and maintaining viable ecosystems.  
Results/Conclusions Research in the semiarid Great Basin indicates that resistance and resilience are strongly influenced by topographic gradients and differ among vegetation types.  At landscape scales, resistance to invasion by non-native annual grasses and to tree expansion typically reflects species’ ecological amplitudes.  Resilience to stressors or disturbances like wildfires, usually increases over gradients of increasing available resources (water and nutrients) and net productivity.  At local scales, resistance and resilience are influenced by a variety of factors including the frequency and severity of disturbance and the ecological memory of an area as indicated by soil characteristics, the composition and abundance of the native community in the above-ground vegetation and seedbank and presence and abundance of invasive species.  Identifying the characteristics of ecosystems that increase resistant to non-native annual grasses and resilience to fire and other disturbances is a critical aspect of prioritizing management activities and determining appropriate treatments.